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CBSE Term II, , 2022, , Contents, CHAPTER, , Cell Cycle and Cell Division, , -, , CHAPTER, , Photosynthesis in Higher Plants, , -, , CHAPTER, , Respiration in Plants, , -, , CHAPTER, , Plant Growth and Development, , -, , CHAPTER, , Breathing and Exchange of Gases, , -, , CHAPTER, , Body Fluids and Circulation, , -, , CHAPTER, , Excretory Products and their Elimination, , -, , CHAPTER, , Locomotion and Movement, , -, , CHAPTER, , Neural Control and Coordination, , -, , CHAPTER, , Chemical Coordination and Integration, , -, , Practice Papers, , -, , -, , Watch Free Learning Videos, Subscribe arihant, , Channel, , þ Video Solutions of CBSE Sample Papers, þ Chapterwise Important MCQs, þ CBSE Updates

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CBSE Term II, , 2022, , Syllabus, EVALUATION SCHEME, THEORY, Units, , Term I, , Marks, , I, , Diversity of Living Organisms: Chapter - , , and, , II, , Structural Organization in Plants and Animals: Chapter, , III, , Cell: Structure and Function: Chapter, , Units, , and, , and, , Term II, , Marks, , III, , Cell: Structure and Function: Chapter -, , IV, , Plant Physiology: Chapter -, , V, , Human Physiology: Chapter, , ,, , and, ,, , ,, , ,, , ,, , and, , Total Theory Term I and Term II, , UNIT-III, , CELL: STRUCTURE AND FUNCTION, , Chapter-, , Cell Cycle and Cell Division, Cell cycle, mitosis, meiosis and their significance., , UNIT-IV, , PLANT PHYSIOLOGY, , Chapter-, , Photosynthesis in Higher Plants, Photosynthesis as a means of autotrophic nutrition; site of photosynthesis, pigments, involved in photosynthesis elementary idea ; photochemical and biosynthetic phases, of photosynthesis; cyclic and non-cyclic photophosphorylation; chemiosmotic, hypothesis; photorespiration; C and C pathways; factors affecting photosynthesis., , Chapter-, , Respiration in Plants, Exchange of gases; cellular respiration - glycolysis, fermentation anaerobic , TCA cycle, and electron transport system aerobic ; energy relations - number of ATP molecules, generated; amphibolic pathways; respiratory quotient., , Chapter-, , Plant - Growth and Development, Growth regulators - auxin, gibberellin, cytokinin, ethylene, ABA.

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CBSE Term II, , 2022, , UNIT-V, , HUMAN PHYSIOLOGY, , Chapter-, , Breathing and Exchange of Gases, Respiratory organs in animals recall only ; Respiratory system in humans; mechanism, of breathing and its regulation in humans - exchange of gases, transport of gases and, regulation of respiration, respiratory volume; disorders related to respiration - asthma,, emphysema, occupational respiratory disorders., , Chapter-, , Body Fluids and Circulation, Composition of blood, blood groups, coagulation of blood; composition of lymph and, its function; human circulatory system - Structure of human heart and blood vessels;, cardiac cycle, cardiac output, ECG; double circulation; regulation of cardiac activity;, disorders of circulatory system - hypertension, coronary artery disease, angina pectoris,, heart failure., , Chapter-, , Excretory Products and their Elimination, Modes of excretion - ammonotelism, ureotelism, uricotelism; human excretory system, structure and function; urine formation, osmoregulation; regulation of kidney, function - renin - angiotensin, atrial natriuretic factor, ADH and diabetes insipidus; role, of other organs in excretion; disorders - uremia, renal failure, renal calculi, nephritis;, dialysis and artificial kidney, kidney transplant., , Chapter-, , Locomotion and Movement, Skeletal muscle, contractile proteins and muscle contraction., , Chapter-, , Neural Control and Coordination, Neuron and nerves; Nervous system in humans - central nervous system; peripheral, nervous system and visceral nervous system; generation and conduction of nerve, impulse., , Chapter-, , Chemical Coordination and Integration, Endocrine glands and hormones; human endocrine system - hypothalamus, pituitary,, pineal, thyroid, parathyroid, adrenal, pancreas, gonads; mechanism of hormone action, elementary idea ; role of hormones as messengers and regulators, hypo - and, hyperactivity and related disorders; dwarfism, acromegaly, cretinism, goiter,, exophthalmic goiter, diabetes, Addison s disease., Note: Diseases related to all the human physiological systems to be taught in brief.

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1, , CBSE Term II Biology XI, , CHAPTER 01, , Cell Cycle and, Cell Division, In this Chapter..., , l, , l, , l, , Cell Cycle, , l, , Mitosis, , l, , Meiosis, , Growth and reproduction are the characteristics of cells in, all living organisms., All cells reproduce by undergoing cell division, i.e. division, of parent cell into daughter cells. Before the division of a, cell, DNA replication and cell growth take place., , Cell Cycle, , The cell cycle is divided into two phases, 1. Interphase, l, , l, , The sequence of events by which a cell duplicates its, genome, synthesises other constituents of the cell and then, divides into two daughter cells is called as cell cycle., l, , Phases of Cell Cycle, A typical eukaryotic cell (human cell) divides once in every, 24 hrs. This duration of cell cycle can vary from an organism, to other organism and also from one cell type to another, e.g., yeast cell progresses through the cell cycle and divides in, only about 90 min., , S, G1, G0, , G2, , ha, , -P, , Me, , M, , An, ap, h, tap ase, ha, s, Prop, hase e, , esis, okin se, Cyt, ha, p, o, l, Te, , se, , Diagrammatic view of a cell cycle indicating formation, of two cells from one cell, , l, , It is the period between the end of one cell division to the, beginning of the next cell division, i.e. between two, successive M-phase., During this phase, cell prepares itself for both cell growth, and DNA replication in an orderly manner. So, it is also, known as preparation phase. It lasts for about 90-96%, i.e., more than 95% of the total duration of cell cycle., During cell cycle of a typical human cell, approx., one, hour is taken by the dividing phase out of 24 hours, duration of one cell cycle., Interphase is further divided into following three substages, on the basis of various synthetic activities, – Gap 1 or G 1 -phase The cell is metabolically active and, continuously grows but does not replicate its DNA. Cell, increases in size and cell organelles (except for, mitochondria, chloroplast and centriole) also increase in, number., – Synthesis or S-phase DNA replication and centriole, duplication take place without any changes in, chromosome number. In animal cells, during the, S-phase, DNA replication begins in the nucleus and the, centriole duplicates in the cytoplasm., – Gap 2 or G 2 -phase Protein synthesis and cell growth, occur. RNA and protein synthesis continues. Cell, organelles like mitochondria and chloroplast increase in, number by duplication.

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2, l, , Some cells in adult animals do not divide, e.g. heart cells, and many cells divide occasionally, e.g. liver cells. These, cells exit the cell cycle at G1 -phase and enter into, quiescent stage (G 0 ), where they remain metabolically, active, but do not divide unless required., , 2. M-phase, , CBSE Term II Biology XI, , (ii) Late Prophase, At the end of the prophase, i.e. during late prophase, the, nucleolus disintegrates gradually and the nuclear envelope, disappears. This disappearance marks the end of the prophase., , 2. Metaphase, l, , Following the interphase, the cell enters the M-phase or, mitotic or mitosis phase., , Mitosis, l, , l, , l, , In this type of division, the chromosomes replicate, themselves and get equally distributed into daughter, nuclei, i.e. the chromosome number in the parental and, progeny cell (diploid) become same. Therefore, it is also, known as equational division., Mitosis is also known as somatic cell division because it, always occur in somatic cells. Mitotic cell division is seen, in the diploid somatic cells in animals, whereas, in plants,, mitotic division is seen in both haploid and diploid cells., It is known to be the phase of actual cell division, which, starts with the division of nucleus, followed by the, separation of daughter chromosomes, i.e. karyokinesis and, terminates with the cytoplasmic division, i.e. cytokinesis., , Disappearance, of nuclear, membrane, Early prophase, , l, , It involves the division of the nucleus., It is further divided into four main substages, i.e. prophase,, metaphase, anaphase and telophase., , Centromere, , Centriole, , (prophase and metaphase), l, , l, , l, , l, , During this phase, condensation of chromosomal material, takes place in order to form a compact mitotic, chromosomes composed of two chromatids, which are, attached together at centromere., The most conspicuous change that takes place during, prophase is the formation of mitotic spindle. The initiation, of mitotic spindle assembly, the microtubules and the, proteinaceous components of the cell cytoplasm helps in, the completion of the process., The mitotic spindle is formed between the two pairs of, centrioles that migrate towards the opposite poles of the, cell., , Each chromosome at this stage is made up of two, longitudinal threads (sister chromatids) and are held, together by the centromere. At the surface of each, centromere disc-shaped structures called kinetochores are, present, which help in the attachment of spindle fibres to, the chromosomes., The chromosomes finally arrange themselves at the equator, in one equatorial plane known as metaphase plate., Following changes are observed during metaphase, (i) Attachment of spindle fibres to kinetochores of, chromosomes., (ii) Movement of chromosomes to spindle equator and its, alignment along the metaphase plate through spindle, fibres to both poles., , (i) Early Prophase, l, , Chromosomes, at equatorial, plate, , Chromosome, Metaphase, Transition to metaphase, A diagrammatic view of stages in mitosis, , 1. Prophase, This phase is known for the initiation of condensation of, chromosomal material, which during the process of, chromatin condensation becomes untangled and finally the, centriole (already duplicated during S-phase of interphase), begins to move towards the opposite poles of the animal cell., For the suitability in study we can categorise prophase as, , Late prophase, , Astral rays, , I. Karyokinesis, l, , It is the phase that starts after the disintegration of nuclear, envelope in the late prophase. The chromosomes spread, out through the cytoplasm of the cell and are seem to be, shortest and thickest. The chromosome can be easily, observed under the microscope., , 3. Anaphase, l, , l, , It is known to be the shortest duration phase, i.e. only of, 2-3 min and is also very simple stage. At the beginning of, this phase, splitting of chromosomes (that are already, arranged at metaphase plate) takes place., The two daughter chromatids now become the, chromosomes of future daughter nuclei and start migrating, towards the opposite poles along the path of their, chromosome fibres.

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3, , CBSE Term II Biology XI, , l, , Thus, following changes are observed during anaphase, , l, , (i) Splitting of centromeres and separation of chromatids., (ii) Movement of chromatids towards the opposite poles., Daughter, chromosomes, , Significance of Mitosis, l, , l, , Pole, , Diagrammatic view of a stage in mitosis (anaphase), l, , 4. Telophase, l, , l, , l, , l, , This is considered to be long and complex phase like, prophase the final stage of mitosis. At the onset of this, stage, the spindle fibres disappear (absorbed in, cytoplasm). The chromosomes decondense and further, lose their individuality after reaching their respective, poles., In general terms, the events of prophase occur just in, reverse sequence during this phase., Now, the individual chromosome cannot be seen and the, chromatin material gets collected in the form of mass in, both opposite poles., Thus, following changes are observed during telophase, (i) The chromosomes gradually uncoil and cluster at, opposite spindle poles. Thus, their individual identity as, discrete elements is lost., (ii) Nuclear envelope slowly reforms around the, chromosomes., , l, , l, , l, , It is restricted to diploid cells only. However in some plants, and social insects, haploid cells also divide by mitosis., It results in the production of diploid daughter cells with, identical genetic combination usually, resulting in genetic, stability., The growth of multicellular organisms is due to mitosis. It, also restores the nucleocytoplasmic ratio and surface, volume ratio of cells., Mitosis in meristematic tissues like apical and lateral, cambium, results in a continuous growth of plants, throughout their life., It helps in cell repair and regeneration of injured and lost, body parts., It forms the basis of asexual reproduction in both plants and, animals., , Meiosis, It involves two sequential cycles of nuclear and cell division, called meiosis-I and meiosis-II., , I. Meiosis-I, l, , Chromosomes, thin and long, Constriction of, cytoplasm, , In some organisms, karyokinesis is not followed by, cytokinesis and it results in the formation of multinucleate, condition called syncytium, e.g. liquid endosperm in, coconut., , l, , During this division, the homologous chromosomes of each, pair separate from each other and reach separate daughter, cells which thereby reduce the number of chromosomes, from diploid to haploid, i.e. from 2n to n. Thus, it is known, as heterotypic division., It is further divided into four phases, i.e. prophase-I,, metaphase-I, anaphase-I and telophase-I., , Prophase-I, Diagrammatic view of a stage in mitosis (telophase), , (iii) Reappearance of nucleolus, Golgi complex and ER also, takes place., , l, , l, , II. Cytokinesis, l, , l, , l, , Mitosis is accomplished by the division of the parent cell, into two daughter cells and by the separation of cytoplasm, into each daughter cell via a process called cytokinesis., In animal cells, it occurs by the appearance of a furrow in, plasma membrane. The furrow deepens and joins in the, centre thus, dividing the cell cytoplasm into two., In plant cells, due to the presence of inextensible cell wall,, cytokinesis is achieved by cell plate formation, (representing the middle lamella between two adjacent, cells). It begins to form in the centre of the cell and grows, outwards to meet the lateral walls., , It is considered to be the most complicated and prolonged, phase as compared to the similar stage in mitosis., This phase is further subdivided into five subphases on the, basis of chromosomal behaviour, i.e. leptotene, zygotene,, pachytene, diplotene and diakinesis., , 1. Leptotene, It is known to be the very first stage of meiotic division, following the interphase., Following features are seen during this phase, Chromosomes become gradually visible under light, microscope., Centrioles start moving towards opposite ends or poles and, each centriole develops astral rays., Each chromosome is attached to the nuclear envelope, through the attachment plate at both of its ends., l, , l, , l

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4, , CBSE Term II Biology XI, , 2. Zygotene, , l, , This is the next substage that takes place after the, completion of the previous one. This is also a short-lived, stage like leptotene., Following changes are seen during this phase, Homologous chromosomes pair up. This pairing is done, in such a way that the genes of the same character, present on the two chromosomes lie exactly opposite to, each other. This process of association is known as, synapsis., It is revealed from the electron micrographic studies, that the formation of synaptonemal complex takes place, by a pair of homologous chromosomes that show, synapsis. The complex so formed, on account of synapsis, forms a bivalent or a tetrad., , l, , l, , Breakdown of nuclear envelope into vesicles occurs., Formation of meiotic spindle (as in mitosis) in order to prepare, the homologous chromosomes for separation also occurs., Diakinesis phase represents the transition from prophase to, metaphase of meiosis-I., , l, , Meiosis-I, , Centrosome, Centrioles, Centrosphere, Cell membrane, Cytoplasm, Nuclear, membrane, Chromatin, Nucleolus, , l, , Interphase, , Chromosomes, , (a) Leptotene, , Asters, Synapsis of, homologous, chromosomes, , 3. Pachytene, This is the stage which immediately follows zygotene, where the pair of chromosomes become twisted spirally, around each other and cannot be distinguished separately., This stage is comparatively long-lived as compared to the, previous two stages., Following changes are seen during this stage, Bivalent chromosomes clearly seen as tetrads., In this stage, sometimes exchange of genes or crossing, over between the two non-sister chromatids of, homologous chromosomes occurs at the points called, recombination nodules, which appear at intervals on, synaptonemal complex. By the end of pachytene,, recombination gets completed leaving the chromosomes, linked at the sites of crossing over., , Centrioles, , Crossing over, , (b) Zygotene, , (c) Pachytene, , Nuclear, membrane, (disappearing), , l, , Nucleolus, (disappearing), , l, , (d) Diplotene, , (e) Diakinesis, , Different stages of prophase-I (meiosis-I) in an animal cell, , Metaphase-I, It is the stage followed by prophase (same as mitosis)., Following changes are observed during this stage, The bivalents during this phase arrange themselves on the two, parallel equatorial plates., The centromeres project little bit towards periphery. Since, there, are two centromeres in each bivalent. Thus, each centromere is, joined by chromosomal fibres., The fibres of the homologous chromosomes are always in the, opposite directions., l, , 4. Diplotene, It is the stage of longest duration of all., Following changes are observed during this stage, In this, the synaptonemal complex appears to get, dissolved, while the chromatids of each tetrad remain, clearly visible., Recombined homologous chromosomes of the bivalents, get separated and form chiasmata (X-shaped structures)., Chiasmata formation is necessary for the separation of, homologous chromosome which have undergone the, process of crossing over., l, , l, , l, , l, , l, , 5. Diakinesis, This is known to be the final stage of meiotic prophase-I., Also known as terminalisation, due to the shifting of, chiasmata towards the end of the chromosomes., Following changes are observed during this stage, Chromosomes become fully condensed., Nucleolus degenerates., , Anaphase-I, l, , l, , l, , This is the next phase after metaphase-I in which homologous, chromosomes break their connection with each other and get, separated., This process of separation of homologous chromosomes is, known as disjunction. The separated chromosomes are, univalents and are also called dyads., On reaching at the end of the anaphase, the two groups of, chromosomes are produced (with each having half number of, chromosomes)., , l, , l, , Note The sister chromatid remains attached at their centromeres on the, separation of the homologous chromosomes.

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5, , CBSE Term II Biology XI, , Telophase-I, , It is in fact considered as incipient interphase., , This is the last stage of meiosis-I in which the chromatids at, each pole of the spindle usually remain uncoiled and get, elongated., Following changes are seen during this stage, , II. Meiosis-II, l, , (i) Homologous chromosomes reach at their respective, poles., (ii) Reappearance of nuclear membrane and nucleolus, takes place., Cytokinesis, , l, , It is the stage during which the cytoplasm and other, organelles divide into two equal halves of cells., Chromosomes, in two, equatorial, plates, , l, , Daughter, cells, , Significance of Meiosis, l, , Metaphase-I, , Anaphase-I, , Telophase-I, , It is known by another term, i.e. homotypic division,, because in this division chromosome number remains, same, as produced in meiosis-I. It is initiated immediately, after cytokinesis. It is often known an equational division., Meiosis-II also resembles a normal mitotic division in, contrast to meiosis-I because it distributes chromatids to, daughter cells (like mitosis)., It also involves four substages, i.e. prophase- II,, metaphase- II, anaphase - II and telophase- II, similar to, mitosis except that these processes occur in two haploid, cells., At the end of meiosis, tetrad of cells, i.e. four haploid cells, are formed., , Cytokinesis, , Stages of meiosis-I, , Interkinesis, This is the stage between the two meiotic divisions, i.e. the, meiosis-I and II. It is generally short-lived. During this, process, no replication of DNA occurs. It is necessary for, bringing true haploidy DNA in daughter cells., , l, , l, , It is the mechanism of conversion of specific, chromosome number of each species in sexually, reproducing organisms across generations., It leads to the formation of gametes which is important for, sexual reproduction., It provides chance for the appearance of new gene, combinations, owing to crossing over. It increases the, genetic variability in the population of organisms from one, generation to the next. Variations help in evolution and, formation of new species.

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6, , CBSE Term II Biology XI, , Chapter, Practice, PART 1, Objective Questions, l, , Multiple Choice Questions, 1. Two basic stages of cell cycle are, , (a) interphase and M-phase /divisional phase, (b) karyokinesis and cytokinesis, (c) prophase, metaphase, anaphase and telophase, (d) G1 , S and G2 -phases, Ans. (a) Cell cycle consists of two basic stages. There is a long, undividing stage called interphase and a short dividing, M-phase., , 2. Cell growth and DNA synthesis are continuous, processes that occur during cell cycle., The given statement is, , 4. During the G 1 -phase of cell division,, (a) RNA and proteins are synthesised for cell growth and, subsequent DNA replication, (b) DNA and proteins are synthesised, (c) Centriole duplicates in the cytoplasm, (d) Cell undergoes duplication, Ans. (a) G1 is the longest phase of the cell cycle in which cell, synthesises RNAs, proteins and other biochemicals for, cell growth and subsequent replication of DNA. While in, G2 -phases, synthesis of RNAs, protein and ohter, biochemicals for spindle formation takes place., , 5. In the diagrammatic view of cell cycle, the, G 0 -phase is represented as, , (a) True, (b) False, (c) Cannot say, (d) Partially true or false, Ans. (d) During the cell cycle, cell growth occurs continuously, by continuous increase in the cytoplasmic content of the, cell. However, DNA replication or synthesis is not a, continuous process as it occurs during a specific stage, only. Thus, given statement is partially true or false., , D, , E, , A, B, C, , 3. Match the following columns., Column I, (Features), A., , Separation of daughter, chromosomes, B. Division of cytoplasm, C. Phase between two, successive M-phases, D. Synthesis phase, , Codes, A B C D, (a) 2 3 1 4, (c) 2 4 1 3, Ans. (c) A–2, B–4, C–1, D–3, , Column II, (Phases of cell division), 1., , Interphase, , 2., 3., , Karyokinesis, S-phase, , 4., , Cytokinesis, , A B C D, (b) 4 1 3 2, (d) 4 2 3 1, , (a) A, (b) B, (c) C, (d) D, Ans. (d) In the given diagram, D represents the G0 -phase of, cell cycle., , 6. Which of the following statements is correct about, mitosis?, (a) Mitosis is also known as equational division, (b) In animals, mitosis occurs in diploid somatic cells only, (c) Plants exhibit mitotic division in both haploid and, diploid cells, (d) All of the above, Ans. (d) All statements are correct about mitosis.

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7, , CBSE Term II Biology XI, , 7. Select the incorrect statement for prophase., (a) Chromosomal material condenses to form compact, mitotic chromosomes, (b) The assembly of mitotic spindle is initiated by the, microtubules, (c) Cells at the end of prophase contain all membrane, bound organelles of the cell, (d) The nucleolus or nucleoli degenerates completely, Ans. (c) Statement in option (c) is incorrect and can be, corrected as, The nucleus, which is the membrane bound organelle in, a cell gets disintegrated., Rest statement are correct., , Ans. (d) Statements III and IV are incorrect and can be, , corrected as, Kinetochore serves as the site of attachment of spindle, fibres during metaphase., During anaphase, each chromosome splits to yield two, daughter chromatids., Rest statements are correct., l, , l, , 11. See the diagrams carefully and identify the, different stages of mitosis (A-C ) by choosing, appropriate option given below., , 8. At which stage of mitosis, the two daughter, chromatids separate from each other, migrate, towards the opposite poles and are now referred to, as chromosomes of the future daughter nuclei?, (a) Prophase, (b) Metaphase, (c) Anaphase, (d) Telophase, Ans. (c) In anaphase, the centromere of chromosomes start to, divide into two forming daughter chromatids with, centromere in each. Daughter chromosomes are, repulsive, so they migrate toward opposite. Spindle fibres, attached to the centromeres, shorten and pull the, chromosomes to the poles., , 9. Mitotic anaphase differs from metaphase in, possessing, (a) same number of chromosomes and same number of, chromatids, (b) half number of chromosomes and half number of, chromatids, (c) half number of chromosomes and same number of, chromatids, (d) same number of chromosomes and half number of, chromatids, Ans. (d) Mitotic anaphase can be distinguished from, metaphase in having same number of chromosomes and, half number of chromatids., , 10. Consider the following statements and choose the, incorrect ones., I. The duplication of centrosome occurs during, S-phase of interphase., II. Asters are the microtubules which radiate out, from each centrosome., III. Kinetochore disappears completely at the start of, metaphase., IV. Each chromosome yields four daughter, chromatids during anaphase., Codes, (a) II and IV, (c) II, III and IV, , (b) I, III and IV, (d) III and IV, , A, , (a), (b), (c), (d), Ans. (a), , C, , B, , A–Metaphase, B–Telophase, C–Interphase, A–Telophase, B–Metaphase, C–Prophase, A–Anaphase, B–Telophase, C–Interphase, A–Telophase, B–Anaphase, C–Prophase, A–Metaphase, B–Telophase, C–Interphase, , 12. Which of the following shows diplotene stage of cell, cycle?, (a) Separation of synapsed homologous chromosomes, except at the site of crossover, (b) Degeneration of nucleolus, (c) Chiasmata shifts towards chromosome ends, (d) All of the above, Ans. (a) The beginning of diplotene stage is marked by, chiasma formation. The chiasma formation is the, indication of crossing over and the beginning of, separation of synapsed homologous chromosomes except, at the site of crossover. The chiasma formation is, associated with the process of terminalisation., , 13. Match the stages of meiosis in Column I to their, characteristic features in Column II and select the, correct option using the codes given below., Column I, (Phases), A. Pachytene, B. Metaphase-I, C. Diakinesis, D. Zygotene, , Column II, (Events), 1. Pairing of homologous, chromosomes, 2. Transition from prophase to, metaphase of meiosis-I, 3. Crossing over takes place, 4. Chromosomes align at equatorial, plate, , Codes, A B C D, (a) 3 4 2 1, (c) 2 4 3 1, Ans. (a) A–3, B–4, C–2, D–1, , A B C D, (b) 1 4 2 3, (d) 4 3 2 1

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8, , CBSE Term II Biology XI, , 14. The given figure is the representation of a certain, event at a particular stage of a type of cell division., Which is this stage?, , Ans. (b) Both A and R are true, but R is not the correct, , explanation of A., G0 -phase is the permanent or temporary exit from the, G1 -phase. Cells in this phase remain metabolically active, but do not proliferate unless called on to do so depending, on the requirement of the organism., , 2. Assertion (A) In mitosis, two identical cells are, produced from a single cell and karyokinesis is, followed by cytokinesis., Reason (R) Cytokinesis is of two types, i.e. by, cell-furrow method and cell-plate method., Ans. (b) Both A and R are true, but R is not the correct, , (a) Prophase-I during meiosis, (b) Prophase-II during meiosis, (c) Prophase of mitosis, (d) Both prophase and metaphase of mitosis, Ans. (a) The given figure shows crossing over, i.e. exchange of, segments between chromosomes. It is a characteristic, process that occur in the prophase-I during meiosis., , 15. Crossing over takes place between which, chromatids and in which stage of the cell cycle?, (a) Non-sister chromatids of non-homologous, chromosomes at zygotene stage of prophase-I, (b) Non-sister chromatids of homologous chromosomes at, pachytene stage of prophase-I, (c) Non-sister chromatids of homologous chromosomes at, zygotene stage of prophase-I, (d) Non-sister chromatids of non-homologous, chromosomes at pachytene stage of prophase-I, Ans. (b) Crossing over takes place between the non-sister, chromatids of homologous chromosomes during the, pachytene stage of prophase-I. This stage is characterised, by the appearance of recombination nodules, which, appear at intervals on synaptonemal complex., l, , Assertion-Reasoning MCQs, Direction (Q. Nos. 1-5) Each of these questions contains, two statements, Assertion (A) and Reason (R). Each of, these questions also has four alternative choices, any one, of which is the correct answer. You have to select one of, the codes (a), (b), (c) and (d) given below., (a) Both A and R are true and R is the correct explanation, of A, (b) Both A and R are true, but R is not the correct, explanation of A, (c) A is true, but R is false, (d) A is false, but R is true, , 1. Assertion (A) Some cells undergo G 0 -phase due to, inactivation of cell cycle., Reason (R) Cells at this stage remain metabolically, active, but no longer proliferate., , explanation of A., Mitosis is the process by which a cell nucleus divides, (karyokinesis) to produce two daughter nuclei containing, identical sets of chromosomes to the parent cell. It is, usually followed immediately by division of cytoplasm, (cytokinesis) to form two daughter cells., In plants, cytokinesis occurs by cell-plate formation, whereas in animals, it occurs by cell furrow formation., , 3. Assertion (A) In animal cells, cytokinesis is, achieved by the appearance of a furrow in plasma, membrane., Reason (R) In plant cells, the formation of the new, cell wall begins with the formation of simple, precursor called cell-plate., Ans. (b) Both A and R are true, but R is not the correct, , explanation of A., In an animal cell, cytokinesis is achieved by the, appearance of a furrow in the plasma membrane. The, furrow gradually deepens and ultimately joins in the, centre thus, dividing the cell cytoplasm into two. This, mode of cytokinesis is called cell-furrow method., Plants cells however, are enclosed by a relatively, inextensible cell wall, therefore they undergo cytokinesis, by a different mechanism. The formation of the new cell, wall begins with the formation of a simple precursor, called the cell plate. It represents the middle lamella, between the walls of two adjacent cells. This mode of, cytokinesis is called cell plate method., , 4. Assertion (A) Diakinesis is the final stage of, prophase-I., Reason (R) Terminalisation of chiasmata occurs in, diakinesis., Ans. (a) Both A and R are true and R is the correct explanation, , of A., Prophase-I ends with terminalisation of chiasmata during, diakinesis. It represents the transition of dividing cells, from prophase to metaphase., Thus, diakinesis is the final stage of prophase-I as, terminalisation of chiasmata occurs in this stage.

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9, , CBSE Term II Biology XI, , 5. Assertion (A) In anaphase-II, chromosomes align at, the equator., Reason (R) The centromere of each chromosome, splits and chromatids separate., Ans. (d) A is false, but R is true. A can be corrected as, , In metaphase-II, the chromosomes align at the single, equatorial plate., l, , Case Based MCQ, Observe the given figure and answer the questions, that follows., , S, G1, , G2, , Me, , ha, -p, M, , An, ap, h, tap ase, ha, s, Prop, hase e, , (a) interphase, (b) M-phase, (c) karyokinesis, (d) cytokinesis, Ans. (a) Interphase is the longest phase of cell cycle, so it, occupied maximum duration in a 24 hours cell cycle., , (iii) The daughter cells formed after M-phase has, (a) increased number of chromosome, (b) same amount of DNA as in G1 -phase, (c) decreased amount of DNA than in G1 -phase, (d) decreased number of chromosomes, Ans. (b) The daughter cells formed after complete mitosis and, cytokinesis will have the same number of chromosomes, and same amount of DNA as their parent cells at, G1 -phase of the cell cycle., , (iv) Duplication of genetic material occurs in, , G0, , esis, okin se, Cyt, ha, p, lo, Te, , (ii) In a 24 hours cell cycle, maximum duration is, occupied by, , se, , (i) In the G 0 -phase of cell cycle,, (a) no division or metabolic activity occurs, (b) division occurs at faster rate, (c) cell is metabolically active, (d) cytokinesis occurs, Ans. (c) Cell entering the G0 -phase, do not divide or multiply, nor synthesise organelles, however it continues to remain, metabolically active., , (a) G1 -phase, (b) G2 -phase, (c) S-phase, (d) M-phase, Ans. (c) The duplication or replication of genetic material, (DNA) occurs during the synthetic or S-phase of cell, cycle. It ensures the equal distribution of genetic material, among the daughter cells., , (v) The G 2 -phase of cell cycle,, (a) helps in chromosome doubling, (b) involved in cell growth, (c) involved in protein synthesis, (d) Both (b) and (c), Ans. (d) G2 -phase of cell cycle occurs immediately before the, cell undergoes division. During this phase, cell growth, continues to occur and the proteins are synthesised for, the preparation of mitosis., , PART 2, Subjective Questions, l, , Short Answer (SA) Type Questions, 1. Name three phases of interphase. Give one major, event of each phase., , Ans. Three main events that occur in interphase are, , (i) G1 -phase is the phase during which cell becomes, metabolically very active. It grows continuously and, prepares itself for DNA replication. Thus, enzymes, and proteins needed for this are formed., (ii) S-phase is the phase during which chromosomes, replicates and prepare themselves for equal, distribution., (iii) G2 -phase is the phase in which synthesis of DNA, gets stopped. However, formation of RNA and, proteins required for mitosis takes place., , 2. There occurs a process in which divisions of, nucleus take place. Identify the process and also, write about its different phases., Ans. Karyokinesis involves the division of nucleus. It is a series, , of uninterrupted changes before forming two daughter, nuclei., Though karyokinesis is a continuous process, it has been, divided into four phases. These are prophase, metaphase,, anaphase and telophase., (NCERT), 3. What is quiescent stage of cell cycle?, Ans. G0 is the quiescent stage of the cell cycle. It is also known, , as inactive stage of the cell cycle. Cells in this stage, remain metabolically active, but no longer proliferate, unless they do not get instruction to do so, depending on, the requirement of the organisms.

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10, , CBSE Term II Biology XI, , 4. Differentiate between G 1 and G 2 -phases., Ans. Differences between G1 and G2 -phases are as follows, , G1 -phase, , G2 -phase, , It is called first growth period., Cell grows in size., , It is post-synthetic phase., Cell prepares to go into, mitotic phase., Occurs after the S-phase., Contains 2N amount of DNA., , Occurs before S-phase., Contains N amount of DNA., , 5. Label the diagram and also determine the stage at, which this structure is visible., , Ans. The diagram shows the transition stage between prophase, , and metaphase stages of mitotic cell division., Dividing centriole, Spindle fibre, , Ans. Centrioles play an important role in formation of, , spindle during cell division. They organise the mitotic, spindle and thus, help in the completion of cytokinesis., They generate the cell’s cytoskeleton and help in the, formation of the mitotic spindles. In organisms with, flagella and cilia, the position of these organelles is, determined by the mother centriole, which becomes, the basal body., , 9. The following statements describe the four main, stages in the process of mitosis., I. The spindle fibres breakdown and the nuclear, membrane forms., II. The chromosomes arrange themselves on the, equator of the cell., III. The spindle forms and the nuclear membrane, disintegrates., IV. The centromere splits and the sister, chromatids migrate to the opposite poles of the, cell., Write the correct sequence of the stages in, mitosis and also name the each stage., Ans. The correct sequence of the stages in mitosis and also, , Chromosomes, moving to, equator, Chromosomes, Transition to metaphase, Metaphase, at equator, , 6. Comment on the statement 'telophase is reverse of, prophase'., (NCERT Exemplar), Ans. In prophase, the chromatin network begins to coil and, appears as a long thread-like structures called chromosomes., Each chromosome consists of two chromatids that disappears, from early prophase to late prophase. The nuclear membrane, also starts disappearing in late prophase. In telophase,, opposite poles of the chromosomes lose their identity and, nuclear membrane is formed around the daughter nuclei., Nucleolus also reappears. So, it is reverse of prophase., , 7. Cell ‘X’ contains 24 chromosomes. It is divided by, mitosis to produce cells ‘ Y’ and ‘Z’. Deduce how many, chromosomes cell Z will contain after division., Cell X, , Cell Y, , 8. State the role of centrioles in cell division., , Cell Z, , Ans. The cell Z will also contain 24 chromosomes after mitotic, , division. Because mitosis is a copying process in which, daughter cells have same number of chromosomes as the, parent has., , name the each stage are as follows, III (Prophase) → II (Metaphase) → IV (Anaphase), → I (Telophase), , 10. Mitosis results in producing two cells which are, similar to each other. What would be the, consequence if each of the following, irregularities occur during mitosis?, (i) Nuclear membrane fails to disintegrate, (ii) Duplication of DNA does not occur, (iii) Centromeres do not divide, (iv) Cytokinesis does not occur, Ans., , (i) If nuclear membrane fails to disintegrate, the, spindle fibres would not be able to reach, chromosomes and they would not move towards, opposite poles of the cell. In certain protozoans,, such as Amoeba, the spindle is formed within the, nucleus and this is called intranuclear mitosis or, pre-mitosis., (ii) If DNA duplication does not occur than cell, might not be able to surpass S-phase of cell cycle, as no chromosome formation will take place, and, will not be able to enter M-(mitotic phase) or if in, case it enters mitosis the cycle will cease., (iii) If the centromeres do not divide, one of the, daughter cell will receive a complete pair of, chromosomes and other cell would not get any of, them. This may result in trisomy., (iv) If cytokinesis does not occur, then multinucleate, condition called coenocyte, syncytium is, produced, as in Rhizopus and Vaucheria, etc.

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11, , CBSE Term II Biology XI, , 11. The following events occur during the various, phases of the cell cycle. Name the phase against, each of the events., (i) Disintegration of nuclear membrane ......... ., (ii) Appearance of nucleolus ......... ., (iii) Division of centromere ......... ., (iv) Replication of DNA ......... ., Ans. (i) Prophase, , (ii) Telophase, (iv) S-phase, , (iii) Anaphase, , 15. What is chiasmata? Mention its significance also., Ans. Chiasmata is X-shaped structure of separated bivalents of, , recombined homologous chromosomes. Chiasmata, formation is necessary for the separation of homologous, chromosomes, which have undergone the process of, crossing over., , 16. The diagram below represents the changes in the, number of chromosomes during several processes, that occur in an animal cell., , 12. Why is mitosis considered a significant event in, living organisms?, Ans. The significances of mitosis cell division are as follows, , (i) It helps in the production of diploid daughter cells, with equal and identical genetic complement., (ii) Mitosis helps in growth of multicellular organisms., (iii) It also helps in maintaining a proper cell size by, dividing an overgrown somatic cell and also helps in, maintaining nucleo-cytoplasmic ratio., (iv) It is helpful in cell repair mechanism, e.g., continuous replacement of the cells like that of the, upper layer of the epidermis cells of the lining of the, gut and blood cells., (v) It is also helpful in producing new cells for healing, wounds and for regeneration., (vi) Mitosis plays an important role in a continuous, growth of plants throughout their life by mitotic, divisions in meristematic tissues, i.e. the apical, meristem and the lateral cambium., , 13. Answer the following questions based upon the, given figure., (i) What type of division is this? Whether meiotic, or/and mitotic and which stage?, (ii) What are A and B?, B, A, , Ans., , n, Y, , X, , (i) It is a meiotic division showing synapsis and it is in, the zygotene stage of prophase-I of meiosis-I., (ii) A–Centromere, B–Chromatid., , 14. Discuss about the synaptonemal complex?, Ans. It is a protein complex, visible with the electron, , microscope that is the physical basis of the pairing of, homologous chromosomes (synapsis) during meiosis. It, is assembled during zygotene as homologous, chromosomes pair up and it is unpaired during diplotene, as homologous chromosomes separate., , 2n, , 2n, , 2n, Y, , n, , (i) Name the process of cell division occurring at, X and Y., (ii) State two differences in the behaviour of, chromosomes between X and Y., Ans. (i) X–Mitosis, , Y–Meiosis, (ii) Differences in between behaviour of chromosomes X, and Y are as follows, (a) In X, there is no association of homologous, chromosomes, but in Y, homologous, chromosomes pair up together to form bivalents, during prophase-I., (b) In X, there is no crossing over as there is no, formation of chiasmata, but in Y, crossing over, occurs at the chiasmata whereby some genes are, swapped between homologous chromosomes., , 17. Give an account on stages of meiosis-I., Ans. Stages of meiosis-I are as follows, , (i) Prophase-I which is divided into five sub-stages, i.e., leptotene, zygotene, pachytene, diplotene and, diakinesis., (ii) In metaphase-I, the bivalents arrange themselves on, equatorial plate with their arms on the plate, but the, centromere is directed towards opposite pole. It is, followed by anaphase-I., (iii) In anaphase-I, the homologous chromosomes repel, each other and move to the opposite poles with both, their chromatids. In this way, each pole gets half the, chromosome number of the parent cell., (iv) Telophase-I in which the nuclear envelope and, nucleolus reappear followed by cytokinesis in which, the cytoplasm and other organelles get divided into, two equal halves of cell., , 18. During meiosis, why sister chromatids do not, separate and migrate to opposite poles., Ans. During interphase-I of meiosis, sister chromatids do not, , separate and migrate to opposite poles as observed in, mitosis because in metaphase-I, the chromosomes are, arranged in a manner that the centromeres homologous

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12, , CBSE Term II Biology XI, , lie on either side of metaphase plate pointing towards, the opposite pole., As a result, a chromosome is connected only to one, spindle pole of its side due to the presence of a single, tractile fibril. Hence, instead of sister chromatids the, homologous chromosome separate apart during, meiosis., , 21. In which phase of meiosis are the following formed?, (i), (ii), (iii), (iv), (v), (vi), , 19. List the differences between metaphase of mitosis, and metaphase-I of meiosis., , Ans., , Ans. Differences between metaphase of mitosis and, , metaphase-I of meiosis are as follows, Metaphase of Mitosis, , Metaphase-I of Meiosis, , The chromosomes at the, metaphase are arranged in, such a way that the, centromeres lie at the, metaphase plate and the, arms of chromosomes are, free., , The chromosomes at the, metaphase (meiosis-I) are, arranged in such a way that the, centromeres of homologous, chromosomes lie on either side, of the metaphase plate, pointing, towards the opposite poles., , A chromosome is, connected to both the, spindle poles due to the, presence of two tractile, fibrils., , In metaphase-I, a chromosome, is connected to only one spindle, pole of its side due to the, presence of a single tractile, fibril., , 20. Distinguish anaphase of mitosis from anaphase-I, of meiosis., , (NCERT), , Ans. Differences between anaphase of mitosis and, , (i) Synaptonemal complex zygotene., (ii) Recombination nodules pachytene., (iii) Appearance/activation of enzyme recombinase, telophase-I/after, meiosis-I., (iv) Termination of chiasmata diakinesis., (v) Interkinesis after telophase-I/before prophase of, meiosis-II., (vi) Formation of dyad of cells pachytene., , 22. An organism has two pair of chromosomes (i.e., chromosome number= 4). Diagrammatically, represent the chromosomal arrangement during, different phases of meiosis-II., Ans., , Daughter, cell 1, Chromatids, , anaphase-I of meiosis are as follows, Anaphase of Mitosis, , Anaphase-I of Meiosis, , Each chromosome, arranged at the metaphase, plate, splits simultaneously, and the two daughter, chromatids migrate, towards the two opposite, poles., The centromere of each, chromosome is towards, the pole with arms of, chromosome trailing, behind., , The spindle fibres contract, and pull the centromeres of, homologous chromosomes, towards the opposite poles., So, each chromosome goes to, opposite pole., , The centromere is not, divided, so half set of the, chromosomes of parent, nucleus go to one pole and, the remaining half set in the, opposite pole., During this stage,, During this stage,, (i) Centromeres split and (i) Homologous, chromatids separate., chromosomes separate., (ii) Chromatids move to, (ii) Sister chromatids remain, opposite poles., associated at their, centromere., , Synaptonemal complex ......... ., Recombination nodules ......... ., Appearance/activation of enzyme recombinase ........ ., Termination of chiasmata ......... ., Interkinesis ......... ., Formation of dyad of cells ......... ., , Centriole, , Spindle fibre, , Prophase-II, , Metaphase-II, , Daughter, cell 2, Anaphase-II, , Telophase-II, , Stages of meiosis-II, , 23. What is the need of meiosis in cell division?, Ans. Needs of meiosis in cell division are as follows, , (i) It is essential for all sexually reproducing organisms., (ii) It occurs in reproductive cells, so that gametes formed, are haploid or have half the number of chromosomes of, those cells which are directly derived from zygote., (iii) Two types of gametes fuse during zygote formation. As, a result, zygote comes to have double the number of, chromosomes contained in gametes. Meiosis maintains, a fixed number of chromosomes in a species by, reducing it to number by half.

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13, , CBSE Term II Biology XI, , 24. Meiosis is advantageous than mitosis as it, produces variations so plays important role in, evolution. What are the stages during which, chances of recombination of genes are increased, during meiosis? Explain these events., Ans. Stages during which recombination of genes occurs in, , meiosis are, (i) Crossing over is exchanged of genes between the, non-sister chromatids of homologous, chromosomes. It occurs at recombination, nodules during pachytene stage of prophase-I of, meiosis-I and is regulated by recombinase, enzyme., (ii) Arrangement of bivalents at the equator of the, spindle during metaphase-I of meiosis., , 25. Discuss about the attributes. Does a chromatid, require to be classified as a chromosome? (NCERT), Ans. In telophase-I of meiosis-I, chromosome number, , becomes half, but the chromosomes are still, composed of two chromatids. If crossing over, occurred, these chromatids are not genetically, identical. They divide in IInd meiotic division., Hence, crossing over is an attribute, which classifies, chromatids as chromosome., , 26. Comment on the statement’ meiosis enables the, conservation of specific chromosome number of, each species even though the process results in, reduction of chromosome number’., (NCERT Exemplar), Ans. Meiosis is the mechanism by which conservation of, , specific chromosome number of each species is, achieved across generations in sexually reproducing, organisms. Even though the process results in, reduction of chromosome number by half, it is, gradually conserved by union of male gamete (n) and, female gamete (n) in next generation., Meiosis also increases the genetic variability in the, population of organisms from one generation to the, next., l, , Long Answer (LA) Type Questions, 1. Briefly describe the significance of cell division., , (NCERT), Ans. Cell division is significant in the following ways, , (i) Cell Multiplication Cell division is a mean of, cell multiplication or formation of new cells from, pre-existing cells., (ii) Continuity It maintains continuity of living, matter generation after generation., (iii) Multicellular Organisms The body of a, multicellular organism is formed of innumerable, cells. They are formed by repeated divisions of a, single cell or zygote. As the number of cells, increases, many of them begin to differentiate,, form tissues and organisms., , (iv) Cell Size Cell division helps in maintenance of a, particular cell size which is essential for efficiency and, control of cell activities., (v) Genetic Similarity The common type of cell division or, mitosis maintains genetic similarity of all the cells in an, individual despite being different, i.e. structurally and, functionally., , 2. Differentiate the process of mitosis in plants and, animals cells., Ans. Differences between the processes of mitosis in plant and, , animal cells are as follows, Animal Cells, , Plant Cells, , Centrioles present at spindle, poles., Cytokinesis by furrowing of, cytoplasm., Microfilament ring brings, about cleavage., Occurs nearly in all tissues., Cell does not change its forms, or nature at the time of, mitosis., Intercellular spaces appear, between the daughter lamella., , Centrioles are absent at, spindle poles., Cytokinesis mostly by cell, plate formation., Microfilaments have no role, in cytokinesis., Occurs mainly at meristems., Cell becomes rounded and its, cytoplasm becomes more, viscous during mitosis., Daughter cells remain, adhered together by middle, lamella., Animal mitosis is controlled by Plant mitosis is usually, certain mitogens., controlled by a hormone, cytokinin., Midbody is formed at the, Equator of the spindle, equator of the spindle., changes into phragmoplast., Furrow extends centripetally. Cell plate grows centrifugally., Asters are formed, No asters are formed, (amphiastral)., (anastral)., , 3. The method of cytokinesis is different in animal and, plant cells. Explain., Ans. Cytokinesis is the division of protoplasms and content after, , nuclear division (i.e. karyokinesis) equally into the daughter, cells., (i) Cytokinesis in Animal Cells The cytokinesis starts at, metaphase stage. The central part of mitoitc spindle, changes to dense fibrous, vesicular structure called, midbody. Simultaneously, microfilaments gather in the, middle region of the cell below cell membrane. This, induces the cell membrane to invaginate or furrow. The, cells divides further by furrowing which deepen, centripetally and cleave the cell into two daughter cells., , Furrow, Mid, body, , Cytokinesis in animal cells

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14, , CBSE Term II Biology XI, , (ii) Cytokinesis in Plant Cells It is different from animal, cells due to the presence of a solid, rigid and, inextensible cell wall. The plant cell cannot undergo, cytokinesis by the furrowing method therefore, it, divides by the cell plate method., The formation of cell plate usually begins during the, late anaphase or early telophase. The formation of a, new wall in plant cells takes place in the centre of, the cell and starts growing outward, towards the, opposite sides in order to reach the already existed, lateral walls., This cell wall with the formation of simple precursor, grows unite it reaches the actual cell walls. The cell, plate divides the cell into two daughter cells and, continues to grow and develop new cell organelles in, both daughter cells., , (iii) The chromosomes become shorter and thicker., Asters, , Zygotene, , Pachytene or Pachynema, (i) The synaptic chromosomes become very intimately, associated., (ii) The pair of chromosomes becomes short and thick., (iii) Crossing over occurs at this stage. Chiasmata are, clearly seen., , Synapsis of, homologous, chromosomes, Crossing over, , Cell, plate, Pachytene, , Cytokinesis in plant cells, , 4. What are the various stages of meiotic prophase-I?, Enumerate the chromosomal events during each, stage., Ans. Prophase-I occurs over a long duration and involves, , several complicated changes in meiotic cell division. It is, important because genetic recombination and variation in, sexually reproducing organism occurs due to the events, of this phase., Leptotene, (i) The chromatin network opens out and threads, become clear., (ii) The chromosomes are thin, slender and long., (iii) Chromosome number is diploid., Centrioles, Chromosomes, , Laptotene, , Zygotene, (i) Corresponding chromosomes become intimately, associated., (ii) The process of pairing is known as synapse. It is so, exact that pairing is not merely between, corresponding chromosomes, but between, corresponding individual units., , Diplotene, (i) Homologous chromosomes start separating from one, another., (ii) Chiasmata tend to slip out of the chromosomes. This, is known as terminalisation of chiasmata., (iii) Chromosomes start separating out, but the, separation is not complete., (iv) Nuclear membrane and nucleolus start disappearing., Nuclear, Membrane, (disappearing), Nucleolus, (disappearing), Diplotene, , Diakinesis, (i) The bivalents condense further and get randomly, distributed., (ii) The separation of paired chromosomes is almost, complete., (iii) Terminalisation of chiasmata is almost complete., (iv) Nuclear membrane and nucleolus disappear., , Diakinesis

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15, , CBSE Term II Biology XI, , 5. Explain meiosis-II in an animal cell., Ans. Meiosis-II in an animal cell explains as follows, , (i) Prophase-II It takes short time. Spindle formation, begins and the chromosomes become short. Two, chromatids are joined to a single centromere., Nuclear membrane and nucleolus disintegrate., (ii) Metaphase-II At the equator, the chromosomes, align at the equator and spindle is formed. The, centromere of every chromosome is joined to the, spindle fibre and centromere also divides., (iii) Anaphase-II The daughter chromosomes are, formed. Chromatids move towards their poles with, the spindle fibres., (iv) Telophase-II Reaching at the poles, chromosomes, form nuclei which are haploid (n) daughter nuclei., Again nuclear membrane is constructed. Nucleolus, now becomes clearly visible., Cytokinesis After meiosis lead to formation of four, daughter cells which are haploid (n)., , Chiasmata or visible, connections between, homologous chromosomes., , Centromeres produce a single, metaphasic plate., , A double metaphasic plate is, formed by centromeres in, metaphase-I, but only one in, metaphase-II., , Chromosomes are independent, and do not show connections., , Homologous chromosomes, are interconnected. Hence,, the chromosomes occur in, pairs or bivalents in, metaphase-I. They are, however, free in, metaphase-II., , Anaphasic chromosomes are, single-stranded., , Chromosomes are, double-stranded in, anaphase-I, but single, stranded in anaphase-II., , Similar chromosomes move, towards the opposite poles in, anaphase., , Dissimilar chromosomes, move toward the opposite, poles both in anaphase-I, and anaphase-II., , Telophase, Telophase is longer and, produces interphase nuclei., , Telophase-I is shorter and, nuclei now enter the, interphase., , Cytokinesis, Cytokinesis follows every, mitosis. It produces two new, cells., , 7. Differentiate between the events of mitosis and, meiosis., Ans. Mitotic cell division results into the increase in the, , Prophase-I is of longer duration, while prophase-II is very brief., Prophase-I is complicated and is, divisible into five substages., Prophase-II is, however very, simple., , Chiasmata are absent., , A centromere splits length-wise Centromeres do not divide, to form two centromeres in the during anaphase-I, but do so, beginning of anaphase., in anaphase-II., , different because in a set of homologous chromosomes,, one of the chromosome belongs to the male parent and, the other comes from the female parent. Therefore, one of, a pair will contain paternal genes and the other will, contain maternal genes., However, a pair of sister chromatids is genetically, identical before crossing over as the chromatids are, formed from the replication of DNA during the S-phase, of interphase. DNA replication ensures that the DNA, content is doubled with identical genes being copied, from the original DNA. Therefore, there is no genetic, variation because there is no exchange of genetic material, between sister chromatids. If crossing over occurs, then it, would be possible for some genes to be exchanged, between the chromatids of homologous chromosomes that, have chiasmata, thus leading to genetic variation., , Meiosis, , Chromosomes of prophase-I, do not show distinct, chromatids., , Anaphase, , Ans. A pair of homologous chromosomes is genetically, , Prophase, Prophase is of shorter, duration., Prophase is simpler and is, hardly distinguishable into, substages., , Each chromosome has two, distinct chromatids., , A centromere is connected with A centromere is connected, both the spindle poles., to one spindle pole in, metaphase-I, but both in, metaphase-II., , genetically different, but a pair of sister chromatids, is genetically identical before crossing over in, meiosis., , Mitosis, , Meiosis, , Metaphase, , 6. Explain, why a pair of homologous chromosomes is, , number of cells that have same genetic composition, whereas meiosis has its importance in the life cycle of, sexually reproducing organisms., , Mitosis, , l, , Cytokinesis often does not, occur after first or, reductional division. It is, then simultaneous after, second division resulting in, four new cells., , Case Based Questions, 1. Direction Read the following passage and answer, the questions that follows., In a lecture on cell cycle and its division, the, teacher taught the two basic stages of cell cycle viz.,, interphase and M-phase. She also taught about the, sub-stages of each basic stage and their, significance.

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16, , CBSE Term II Biology XI, , (i) What is an average duration of cell cycle in humans, and yeast ?, Ans. The average duration of cell cycle in humans is, , 24 hours and in yeast, it is 90 minutes., , (ii) Mention the name of three sub-stages of interphase., Ans. The three sub-stages of interphase are Gap 1 (G1 )-phase,, , Synthesis (S)-phase and Gap 2 (G 2 )-phase., , (iii) What would be the amount of DNA and, chromosome in each sub-stage of interphase, if the, initial amount is 2C and 2n, respectively?, Ans. The amount of DNA and chromosomes in G1 , S,, , G 2 -phases would be as follows, G1 -phase : 2C, 2n, , (ii) State the stage of mitosis at which the cytokinesis, begins in the animal cells., Ans. In animal cells, cytokinesis starts at metaphase. They, , typically divide by furrowing or by the appearance of, furrow in the plasma membrane. This is also known as, cleavage., , (iii) Can a cell undergo cytokinesis before it has, divided its nuclear content?, Ans. No, cytokinesis occurs after karyokinesis, i.e. after the, , parent cell has doubled up its nuclear content for its, distribution into daughter cells., , (iv) How formation of phragmoplast related to, cytokinesis?, Ans. In higher plants, cytokinesis takes place by cell plate, , S-phase : 4C, 2n, G 2 -phase : 4C, 2n, Thus, the number of chromosomes remain the same, throughout the cell cycle, but the amount of DNA gets, doubled in S-phase., , (iv) Define the terms karyokinesis and cytokinesis and, when does these processes occur in cell cycle?, Ans. Karyokinesis is the division of nucleus, in which the, , daughter chromosomes gets separated. It occurs after the, end of G 2 -phase. Cytokinesis is the division of cytoplasm, and it occurs immediately after karyokinesis., , (v) Which part of the human body should one use to, demonstrate stages in mitosis?, Ans. All the cells in the human body are somatic cells except, , germinal cells in the male and female reproductive organs., The somatic cell divides by mitotic cell division for growth, and regeneration. These can be used to demonstrate, mitosis., , 2. The cytokinesis in plant cell and animal cell during, mitotic cell division is depicted in the figure given, below., , method. In this method, small vesicles of Golgi complex, are assembled at the equator. Here, spindle persists for, some time called phragmoplast., , (v) In which type of cell, karyokinesis is not followed, by cytokinesis?, Ans. In a syncytium (multiple nucleus in a cell), karyokinesis, , is not followed by cytokinesis., , 3. Direction Read the following passage and answer, the questions that follows., Amrita and her mother planted small seedling of, plant in the soil in their garden. After few months,, while playing with her friends Amrita observed, that the seedlings which they planted had grown, into a mature and flourishing plant. Amrita was, curious to know this and asked her mother about, this., (i) Name the process that causes growth in living, organisms., Ans. Mitosis is the process, which helps in the growth of, , living organisms., , (ii) Discuss about the process that how growth occurs, in living organisms., Furrow, , Cell, plate, , Midbody, , Answer the questions given below., (i) What is cell plate?, Ans. Cell plate represents the middle lamella between the walls, , of two adjacent cells within which actual cell wall, formation takes place., , Ans. Mitosis brings about growth in both multicellular and, , unicellular organisms. In multicellular organisms,, mitosis causes overall body growth and in unicellular, organism, its causes multiplication., , (iii) Analyse and write about the common site of, mitosis in plants as well as in animals., Ans. The common sites of mitosis cell division in plants are, , meristematic regions, e.g. stem tip, root tip, embryo,, leaves, flowers, fruits, etc. In animals, mitosis occurs in, skin epidermis, bone marrow and embryo.

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17, , CBSE Term II Biology XI, , (iv) If a tissue has 1024 cells at a given time, how many, cycles of mitosis had the original parental single cell, undergone?, (NCERT Exemplar), , 5. The figure given below depicts a sub-stage in, prophase of meiosis-II., , Ans. 10 (2 n , where n = 10 generations). Thus, 10 cycles of mitosis, , are required for 2 parental cells to form 1024 cells., , (v) Can there be mitosis without DNA replication in, S-phase?, , Nuclear, membrane, (disappearing), , Ans. Mitosis cannot occur without DNA replication in S-phase, , because the trigger for mitosis takes place due to the, disturbance in nucleocytoplasmic ratio caused by DNA, replication in S-phase., , 4. Direction Read the following passage and answer the, questions that follows., A biology student asked his teacher that why two, individuals of same population does not look similar., The teacher told him about the concept of meiosis, and crossing over. The teacher also mentioned that, meiosis occurs in two stages which differ, significantly., (i) When does the crossing over occur in humans and, name the type of cells involved in it., Ans. Crossing over occurs during the pachytene stage of, , prophase-I of meiosis-I. It occurs in the reproductive cells, of human body., , (ii) Name the site at which the crossing over occur, between homologous chromosomes., Ans. Crossing over occurs at the recombination nodule. It is, , formed between the non-sister chromatids of homologous, chromosomes., , (iii) How many daughter cells are produced at the end of, meiosis-I and II, respectively?, Ans. At the end of meiosis-I and meiosis-II, two and four, , daughter cells are produced, respectively., , (iv) Name the stage between the two meiotic divisions., Ans. The stage between two meiotic divisions is called, , interkinesis., , (v) Mention one striking difference between the, anaphase-I and anaphase-II stages of meiosis., Ans. Difference between the anaphase-I and anaphase-II stages, , of meiosis is, During anaphase-I, the homologous chromosomes separate, and the sister chromatids remain intact at centromere., Whereas in anaphase-II, the sister chromatids of the, chromosomes separate due to the splitting of centromere., , Nucleolus, (disappearing), , (i) ‘This phase is characterised by crossing over, where non-sister chromatids of homologous, chromosomes exchange segments’., Is the above statement correct? Provide reason, for your answer., Ans. The given statement is incorrect and can be corrected, , as, The stage depicted is diplotene. It is characterised by, the formation of structure called chiasma., , (ii) The phase before this is identified as leptotene. If, yes/no, provide any two characteristic features,, which are related with this phase?, Ans. No, the phase before diplotene is pachytene., , Characteristic features, which are related with this, phase are as follows, (a) At this stage, bivalent chromosomes appear as, tetrad., (b) Crossing over occurs in this phase., , (iii) What changes are observed in next stage?, Ans. The stage next to diplotene is diakinesis., , Following changes observed during this stage, (a) Chromosome becomes fully condensed., (b) Nucleolus degenerates., , (iv) What type of chromosomes are called homologous, pair?, Ans. Homologous chromosomes are the pair of chromosomes, , which comes from each parent. These are similar in, length, gene position and location of the centromere., , (v) What indicate the beginning of diplotene stage of, prophase-I?, Ans. In the beginning of diplotene stage of prophase-I,, , synaptonemal complex dissolutes and recombined, homologous chromosomes separate from each other.

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Chapter Test, Multiple Choice Questions, , 1. Which one is the correct sequence of a cell cycle?, (a), (b), (c), (d), , G1-phase, M-phase and G 2-phase, M-phase, S-phase and divisional phase, G1-phase, synthesis phase and G 2-phase, M-phase, G 2-phase and divisional phase, , 2. What will be the DNA content and number of, chromosomes in a cell after S-phase as compared to, the gamete of the same organism?, (a), (b), (c), (d), , Same DNA content, but double chromosome number, Four times DNA content, but double chromosome number, Same DNA content, but half chromosome number, Half DNA content, but double chromosome number, , 3. A stage in cell division is shown in the figure. Select the, answer, which gives correct identification of the stage, with its characteristics., , Assertion-Reasoning MCQs, Direction (Q. Nos. 1-3) Each of these questions contains, two statements, Assertion (A) and Reason (R). Each of, these questions also has four alternative choices, any one, of which is the correct answer. You have to select one of, the codes (a), (b), (c) and (d) given below., (a) Both A and R are true and R is the correct explanation of A, (b) Both A and R are true, but R is not the correct explanation, of A, (c) A is true, but R is false, (d) A is false, but R is true, , 1. Assertion (A) Cell normally proceed to mitosis without, interruption, once it enters the G2 -phase., Reason (R) Replicated chromosomes (DNA) are, distributed to daughter nuclei by a complex series of, events under genetic control., , 2. Assertion (A) Mitosis restores the nucleocytoplasmic, ratio., Reason (R) It is significant in the life of an organism,, especially in the growth of multicellular organism., , 3. Assertion (A) A cell after telophase-II does not enter, another interphase., Reason (R) Gametes or Spores are formed after, telophase-II., , Short Answer Type Questions, , 1. (i) Two key events take place during S-phase in animal, cells, i.e. DNA replication and duplication of centriole., In which parts of the cell, do these events occur?, (a), , Telophase, , – Nuclear envelope reforms, Golgi complex, reforms, , (b) Late anaphase – Chromosomes move away from equatorial, plate, Golgi complex not present, (c), , Cytokinesis, , (d) Telophase, , – Cell plate formed, mitochondria distributed, between two daughter cells, – Endoplasmic reticulum and nucleolus not, reformed yet, , 4. Which one of the following events does not occur, during zygotene?, (a), (b), (c), (d), , Formation of synaptonemal complex, Pairing of chromosomes, Appearance of bivalents, Involvement of recombinase, , 5. Select the option which correctly identifies the similarity, between mitosis and meiosis cell division., (a), (b), (c), (d), , Pairing of homologous chromosomes, Required in all types of cells, S-phase occurs before M-phase, Separation of paired chromosomes, , (NCERT Exemplar), (NCERT), , (ii) Distinguish cytokinesis from karyokinesis?, , 2. Colchicine is known to be the mitotic poison. How?, 3. (i) What does a bivalent of meiosis-I consist of ?, (ii) At the following stage of meiosis, the chromosomes, appear to be beaded. Can you find out the stage?, , 4. The second meiotic division is similar to mitosis as it, results in the separation of the sister chromatids., However, it also differs from mitosis. Explain how?, , Long Answer Type Questions, , 1. (i) Both unicellular and multicellular organisms undergo, mitosis. What are the differences, observed in the process between the two?, (NCERT Exemplar), , (ii) Differentiate between S-phase and G2 -phase., , 2. (i) Write brief note on the following., (a) Synaptonemal complex, , (b) Metaphase plate, , (ii) Name a cell that is found arrested in diplotene stage, for months and years. Comment in 2-3 lines how it, completes cell cycle?, (NCERT), , Answers, Multiple Choice Questions, 1. (c), , 2. (b), , 3. (a), , 4. (d), , Assertion-Reasoning MCQs, 1. (d), , 2. (b), , 3. (a), , 5. (c), , For Detailed Solutions, Scan the code

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19, , CBSE Term II Biology XI, , CHAPTER 02, , Photosynthesis, in Higher Plants, In this Chapter..., l, , Chloroplast : The Site of Photosynthesis, , l, , Dark Reaction (Biosynthetic Phase), , l, , Pigments Involved in Photosynthesis, , l, , Calvin Cycle (C3-Pathway), , l, , Mechanism of Photosynthesis, , l, , The C4-Pathway, , l, , Light Reaction, (The Photochemical Reaction), , l, , Factors Affecting Photosynthesis, , All animals including human beings depend on plants for, their requirement of food. Green plants can synthesise, their own food (autotrophs), but all other organisms, depend on them directly or indirectly for their food needs., Green plants carry out photosynthesis. It is a, physio-chemical process by which they use the light, energy (from sun) to manufacture organic compounds., Photosynthesis is an important phenomenon due to the, following two reasons, (i) It is the primary source of food on the earth., (ii) It is responsible for the release of oxygen into the, atmosphere by green plants., Photosynthesis in plants requires chlorophyll, light and, CO2 . In the basic reaction of photosynthesis, water and, carbon dioxide combine to form carbohydrates and, molecular oxygen. This reaction is driven by light energy., Light energy, , 6CO2 + 6H2 O  , → C 6 H12 O 6 +6O2, Chlorophyll, , Chloroplast : The Site of, Photosynthesis, These are the green plastids that function as the site of, photosynthesis, i.e. help in the synthesis of organic food. The, process of photosynthesis takes place in the green leaves of the, plants because chloroplasts are abundantly present in the, mesophyll cell of the leaves., Chloroplast aligned themselves with their flat surfaces parallel to, the walls of the mesophyll cells under optimum light intensities, and they are perpendicular to the walls of the mesophyll cells, when the intensity goes very high, just to prevent, photooxidation of chlorophyll-a., Chloroplast is double membrane bound, DNA and ribosome, containing semiautonomous cell organelle. Internally, a, chloroplast contains a proteinaceous matrix or fluid called, stroma, the membrane system called lamellae or thylakoids. At, some places, the thylakoid gets aggregated to form stacks of, discs, called grana.

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20, , CBSE Term II Biology XI, , Pigments Involved in, Photosynthesis, The pigments involved in the process of photosynthesis are, called photosynthetic pigments. These pigments provide, different shades of green in the leaves in different plants or in, the leaves of same plant., These pigments can easily be separated out by, chromatographic technique (paper chromatography). On the, basis of their significance, the photosynthetic pigments are of, two types, (i) Primary Pigments The pigment forms the main, molecule of photosystem, e.g. chlorophyll- a, b., (ii) Accessory Pigments These support the function of, primary pigments, e.g. xanthophylls and carotenoids., A chromatographic separation of the leaf pigments shows that, it is not only the single pigment, which is responsible for the, colour in the leaves. Instead different shades in leaves are, due to four different pigments that have different ability to, absorb light at specific wavelength., Different pigments present in leaf are described below, (a) Chlorophyll-a (C 55 H72 O 5 N 4 Mg) This is bright or, blue-green in the chromatogram. It is known to be the, chief plant pigment associated with photosynthesis., (b) Chlorophyll-b (C 55 H70 O 6 N 4 Mg) This is yellow-green, in colour., , Absorption Spectrum, It is the curve that shows the amount of different, wavelength of lights absorbed by a substance (photosynthetic, pigment). The graph given below shows the ability of, chlorophyll-a to absorb lights of different wavelengths., Chlorophyll-a shows the maximum absorption peak at, 450 nm and also shows another peak at 650 nm., Absorbance of light by, chloroplast’s pigments, , Diagrammatic representation of an electron micrograph, of a section of chloroplast, , (c) Xanthophylls They are yellow in colour. These, pigments are oxidised carotenoids., (d) Carotenoids They are yellow to yellow-orange in, colour. They are also known as ‘antenna pigment’., Chlorophyll is the most abundant plant pigment found in the, plants in the world. It contains magnesium (Mg 2+ ) metal as, its constituent. Chlorophyll-a is found in all, photosynthesising cells., , Chlorophyll-b, Carotenoids, Chlorophyll-a, , 400, , 500, , 600, , 700, , Wavelength of light in nm, , Graph showing the absorption spectrum of, chlorophyll-a, b and the carotenoids, , Absorption spectrum is constituted by the pigments like, violet, blue, orange and red (400-500 and 600-700 nm) lights., The emission spectrum is constituted by yellow and, yellow-green pigment (500-550 nm)., Action Spectrum, It is the curve that depicts the relative rates of, photosynthesis at different wavelengths of light. Now,, another graph given below, shows the wavelength at which, maximum photosynthesis occurs at blue, violet and red, wavelength in a plant (which is shown by chlorophyll-a)., Rate of photosynthesis, (measured by amount, of O2 release), , The clear division of labour occurs within the chloroplasts,, i.e. the membrane system is responsible for trapping of solar, energy and the synthesis of ATP and NADPH (photochemical, phase), whereas the stroma has enzymes, which are, responsible for the reduction of carbon dioxide into, carbohydrates and formation of sugars., As the former set of reactions is dependent on light so they, are called light reactions, while the latter is dependent on, the products of light reactions, i.e. ATP and NADPH (and are, independent from direct sunlight), thus are called dark, reactions., , 400, , 500, 600, 700, Wavelength of light in nm, , Graph showing action specturm of photosynthesis

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21, , CBSE Term II Biology XI, , Hence, this concludes that chlorophyll-a is the chief pigment,, which is majorly responsible for the photosynthesis. The another, graph given below shows the action spectrum of, photosynthesis, which coincide closely to the absorption, spectrum of chlorophyll., Rate of photosynthesis, Absorption of light, , Photosystems, , Light absorbed, , 400, , 600, 500, Wavelength of light in nm, Superimposed on absorption, spectrum of chlorophyll-a, , During the course of light reaction, light is trapped by, photosynthetic pigments present in the quantasomes of grana, thylakoids., These photosynthetic pigments are organised into two, discrete photochemical Light Harvesting Complexes (LHCs), known as Photosystem-I (PS-I) and Photosystem-II (PS-II)., , 700, , All three graphs together shows that the major part of the, photosynthesis takes place in the blue and red regions, while, some of the photosynthesis takes place at other wavelengths, also in the visible spectrum., Apart from chlorophyll-a (the major pigment,) which is, mainly responsible for trapping of light, other thylakoid, pigments such as chlorophyll-b, xanthophylls and carotenoids, also absorb light, transferring energy to chlorophyll-a. These, pigments are called accessory pigments., These pigments enable a wider range of wavelength of, incoming light to be utilised for photosynthesis and also, provide protection to chlorophyll-a from photooxidation., Note Photosynthetically Active Radiation (PAR) The region of, wavelength in which photosynthesis takes place normally. It, ranges from 400-700 nm., , Mechanism of Photosynthesis, It was observed that the rate of photosynthesis is directly, proportional to the intensity of light, i.e. rate increases with, the increase in intensity of light till the plant achieves a, saturation point., The process of photosynthesis takes place in following, two steps, , Light Reaction, (The Photochemical Phase), Light reaction includes the following steps, i.e. absorption of, light, splitting of water, release of oxygen and finally the, formation of high energy chemical intermediates, i.e. ATP, and NADPH., , The light harvesting complexes or photosystems are made, up of hundreds of pigment molecules bounded by proteins., Each photosystem has a photocentre or reaction centre,, where actual reaction takes place., This reaction centre contains a special chlorophyll-a, molecule. It is fed by hundred other pigment molecules and, it forms the light harvesting system called antennae. These, antennae molecule absorb light of different wavelength, but, shorter than reaction centre in order to make photosynthesis, more efficient., , The light harvasting complex, , The reaction centre is different in both the photosystem as, given below, (i) In PS-I, the reaction centre or chlorophyll-a has peak, of absorption at 700 nm, known as P700., (ii) In PS-II, the reaction centre has absorption peak at, 680 nm hence, called P680., Note These photosystems are, named according to the sequence of, their discoveries and not in the sequence in which they function, during the light reaction., , The Electron Transport, In PS-II, the chlorophyll-a absorbs 680 nm wavelength of red, light, causing electrons to become excited and jump into, another orbit., These electrons are picked up by an electron acceptor, which, passes them to an electrons transport system consisting of, cytochromes., These electrons are not used up, but are passed on to the, pigments of PS-I.

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22, , CBSE Term II Biology XI, , The electrons in the reaction centre PS-I are also excited, when they receive red light of wavelength 700 nm and are, transferred to another acceptor molecule., These electrons move down hill to a molecule of energy rich, NADP + . The addition of these electrons reduces, NADP + to NADPH + H + ., , carrier, i.e. circulation takes within the photosystem and, the phosphorylation occurs due to cyclic flow of, electrons., Note When non-cyclic form of photophosphorylation gets stopped, under certain conditions, the cyclic photophosphorylation keeps, operating and photosynthesis continues for some time., , The cyclic photophosphorylation takes place in the, stromal lamellae of the chloroplast. This happens, because the stromal lamellae do not possess enzyme,, NADP reductase (essential for reducing NADP + to, NADPH) and PS-II. Thus, the excited electrons in the, cyclic photophosphorylation does not pass on to, NADP + instead it gets cycled back to the PS-I, complex., , This whole scheme of transfer of electrons, starting from, PS-II, uphill to the acceptor and finally down hill to, NADP + causing it to reduced to NADPH + H + is called, Z-scheme, due to its characteristic shape., , Light, , Photosystem-I, e– acceptor, , e– acceptor, , ADP+iP ATP, , NADPH, NADP+, , Photosystem-I, e- acceptor, , Electron, transport, system, , ADP, +iP, , Light, , ATP, , Photosystem-II, , LHC, , Electron, transport, system, , LHC, H2 O, , 2e– + 2H+ +[O], , Chlorophyll, , Cyclic photophosphorylation, , Splitting of Water, PS-II supplies electrons continuously by splitting of water., Water is split into 2H + , [O] and electrons in the presence of, light (i.e. photolysis). This creates oxygen, one of the net, products of photosynthesis., 2H2 O → 4H + + O2 + 4e −, Photophosphorylation, Photophosphorylation is the process through which ATP is, synthesised from ADP and inorganic phosphate (Pi) by the, cell organelles (like mitochondria and chloroplasts) with the, help of energy from solar radiation., The process of photophosphorylation is of two types, (i) Non-cyclic Photophosphorylation It is a type of, photophosphorylation in which both the photosystems, (PS-I and PS-II) cooperate in light driven synthesis of, ATP. During this cycle, the electron released from, PS-II does not return back to it. Hence, it is known as, non-cyclic photophosphorylation. Thus, both NADPH, and ATP are formed during this reaction, are used in, light independent reaction and are called reducing, power., (ii) Cyclic Photophosphorylation It is the type of, photophosphorylation in which only PS-I is taking part, and the electron released from the reaction centre P700, returns back to it after passing through a series of, , PS-I, , P700, , Z-scheme of light reaction, , Chemiosmotic Hypothesis, It explains the mechanism of ATP synthesis in chloroplast., ATP synthesis is related to development of a proton gradient, across a membrane., The steps that cause a proton gradient to develop are, The proton or hydrogen ions that are produced by splitting, of water, accumulate within the lumen of thylakoids., As electrons move through the photosystems, protons are, transported across the membrane. This is because the, primary acceptor of electron, which is located towards the, outer side of membrane transfers its electrons not to an, electron carrier, but to H carrier. Hence, this molecule, removes a proton from the stroma, while transporting an, electron. The proton is then released into the inner side of, the membrane., The NADP reductase enzyme is located on the stroma side, of membrane. The protons are necessary for the reduction, of NADP + to NADPH + H + . These protons are also, removed from the stroma., Hence, within the chloroplast, protons in the stroma, decreases in number, while in the lumen there is, accumulation of protons. This creates a proton gradient, across the thylakoid membrane., l, , l, , l, , l

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23, , CBSE Term II Biology XI, , l, , l, , The breakdown of gradient provides enough energy to cause a, change in F1 -particle of the ATPase, which makes the enzyme, to synthesise several molecules of energy packed ATP. ATPase, enzyme catalyses the formation of ATP., The ATP is used immediately in biosynthetic reaction, taking, place in stroma, responsible for fixing CO 2 and synthesis of, sugar., , Stroma (low H+), , +, , NADP +H NADPH, , H+, , Light, P680, PS-II, , Light, , Cytochrome, b6f, , PQ, PQH, , e, , Plas, , H 2O, Oxidation, of water, , to, , on, quin, , H+, , FNR, Fd, P700, PS-I, , PC, Plasto, cyanin, , 1 O +H+, 2, 2, H+, , H+, High, Electroche, mical, Potential, Gradient, Thylakoid, membrane, Stroma, , Low, , ATP, Synthase, , H+, Lumen, (high H+), , H+, , (ii) C 4 -Pathway This pathway is followed or shown by, the plants in which first product of CO2 -fixation is, a C 4 acid, i.e. OAA., , Calvin Cycle (C 3 Pathway), This is a cycle biochemical pathway of reduction of CO2, or photosynthetic carbon, cycle which was discovered by, Melvin Calvin in 1950., The Calvin cycle runs in all photosynthetic plants, no, matter they show C 3 , C 4 or any other pathway. It occurs, in stroma of the chloroplast., , Primary Acceptor of CO2 in, C 3 Pathway, After a long research and conducting many experiments, it was concluded by the scientists that in C 3 pathway, the, acceptor molecule is a 5-carbon ketose sugar, i.e., Ribulose 5-Bisphosphate (5 RuBP)., Calvin or C 3 cycle has following three major steps, 1. Carboxylation, , CF0, , CF1, , ADP + Pi, , ATP, H+, ATP synthesis through chemiosmosis, , Dark Reaction (Biosynthetic Phase), This phase does not require direct sunlight, but it depends on the, products of the light reaction, i.e. ATP and NADPH beside CO2, and water that drive the processes leading to the synthesis of food, more accurately, the sugars (glucose is the first product of, photosynthesis)., Note The O 2 thus, produced in the light reaction of the photosynthesis, diffuses out of the chloroplast and is released into atmosphere., , As soon as the light becomes unavailable, the biosynthetic process, continues for some time and then eventually stops and starts again, if the light is made available., Originally, this process is known as carbon-fixation or, Photosynthetic Carbon Reduction (PCR) cycle., These reactions are sensitive to temperature change, but are, independent of light, hence called dark reaction. This takes place, in the stroma of chloroplast., Thus, assimilation of CO2 during photosynthesis is of two main, types, (i) C 3 -Pathway This pathway is followed by the plants when, first product of CO2 -fixation is a C 3 acid, i.e. PGA., , It is the most crucial step of the Calvin cycle. In this,, fixation of CO2 molecule takes place in the form of, carboxylation of RuBP (5C). This reaction is catalysed by, the enzyme RuBP carboxylase. This finally leads to the, formation of two molecules of 3-Phosphoglyceric Acid, (3PGA). As the RuBP carboxylase enzyme also has an, activity of oxygenation., Thus, it is more commonly known as RuBP, carboxylase-oxygenase or RuBisCO., RuBisCO, CO2 + RuBP + H2 O →, 2 (3-PGA), Mg2 +, Atmosphere, Ribulose-1,5bisphosphate, , ADP, , CO2 + H2O, , 1 Carboxylation, 3 Regeneration, 3-Phosphoglycerate, ATP, 2 Reduction, Triose, phosphate, Sucrose and starch, , ADP, +, +, Pi + NADP, , Calvin cycle (C 3 pathway), , ATP, +, NADPH

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24, , CBSE Term II Biology XI, , 2. Reduction, After the carboxylation reaction, reduction of PGA takes place, through a series of reactions leading to the formation of, glucose. In this step, the ATP (as energy source) and NADPH, (hydrogen atom carrier) are utilised. It is to be noted that 2, molecules of ATP and 2 molecules of NADPH are utilised in, this step for phosphorylation and for the reduction of CO2 ,, respectively. Hence, the fixation of 6 molecules of CO2 and 6, turns of the cycle are required in order to release one molecule, of glucose from the pathway., 3. Regeneration, For the continuous and uninterrupted functioning of the, Calvin cycle, there must be a regular supply of ATP, NADPH, and also sufficient amount of RuBP is required. The, regeneration of RuBP (CO2 acceptor) is a complex process and, involves many types of sugar starting from triose (3C) to, heptose (7C)., The regeneration step requires one ATP molecule for, phosphorylation. Hence, for every CO2 molecule that enters, the Calvin cycle, are required 3 molecules of ATP and, 2 molecules of NADPH., Note The cyclic phosphorylation takes place in order to meet the difference, in the number of ATP and NADPH used in the dark reaction., , Thus, in order to produce one molecule of glucose through the, Calvin pathway, 18 ATPs and 12 NADPHs are required., This can be easily understood by the following table given below, , C4-plants have bundle sheath cells in their leaves called as, ‘Kranz anatomy’., In Kranz anatomy, bundle sheath cells form several layers, around the vascular bundles, having a large number of, chloroplasts, thick walls impervious to gaseous exchange, and no intercellular spaces., The Hatch and Slack pathway is also a cyclic process, which, occurs in the following steps, Step I In C 4 -plants, the initial fixation of CO2 occurs in, mesophyll cells. The primary acceptor of CO2 is, Phosphoenol Pyruvate (PEP)., Step II It combines with CO2 in the presence of an, enzyme, phosphoenol pyruvate carboxylase or, PEP carboxylase (PEPCase) to form the first stable, (a 4 carbon organic acid) product of C 4 pathway,, i.e. the Oxaloacetic Acid (OAA)., Step III The compound (OAA) are transported to the, bundle sheath cells where they are broken down,, releasing CO2 and a 3-carbon molecule., Step IV The 3-carbon compound is again transported back, to the mesophyll cells where regeneration of PEP, takes place, thus completing the cycle., Atmospheric CO2, Mesophyll cell, , Plasma membrane, Phosphoenol, HCO3– Pyruvate, , In, , Out, , 6 CO2, , 1 glucose, , 18 ATP, , 18 ADP, , Fixation, , 12 NADPH, , 12 NADP, , C4 acid, , The C 4 -Pathway, , C 4 -pathway is present in plants that are adapted to live in dry, tropical regions., These plants (C 4 -plants) have the C 4 acid, i.e. oxaloacetic acid, as the first CO2 -fixation product. They use the C 3 -pathway or, the Calvin cycle as the main biosynthetic pathway., Characteristics of C 4 -plants, They have a special type of leaf anatomy., They can tolerate high temperatures., They show a high light intensities., They lack a process called photorespiration and have greater, productivity of biomass., , Cell wall, , Regeneration, C3 acid, , Plasmodesmata, Bundle, sheath cell, , Transport, , Transport, , Fixation by, C4 acid Calvin cycle, CO2, Decarboxylation, , C3 acid, , l, , l, , l, , l, , Diagrammatic representation of the Hatch and Slack Pathway, , The CO2 thus, released in the bundle sheath cells, enters the C 3 or the Calvin cycle (common, pathway to all plants).

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25, , CBSE Term II Biology XI, , Photorespiration, , Characteristics, , C3-plants, , C4 -plants, , It is a process, which creates an important difference, between C 3 and C 4 -plants., It is a process which occurs in C 3 -plants only., In this, O2 binds to the RuBisCO and decreases CO2, fixation., Then, RuBP binds with O2 instead of forming PGA and, form one molecule of phosphoglycerate and, phosphoglycolate. This pathway is called photorespiration., In this pathway, there is neither synthesis of sugars nor of, ATP. Rather, it results in release of CO2 with the, utilisation of ATP. So, photorespiration is a wasteful, process here., , CO2-fixation rate under, high light conditions, , No, , Yes, , Presence of, photorespiration at low, light intensities, , No, , No, , Presence of, photorespiration at high, light intensities, , Yes, , No, , Presence of, photorespiration at low, CO2 concentration, , Yes, , No, , Presence of, photorespiration at high, CO2 concentration, , No, , No, , Optimum temperature, , 20-25° C, , 30-40 ° C, , Geographical location of, plants, , Present, everywhere, , In tropical climate, , Examples, , Mango and guava Maize and, sugarcane, , l, , l, , l, , In C4 -plants, photorespiration does not occur, this is because, they have a mechanism that increases the concentration of, CO2 at the enzyme site., C 4 -acid from mesophyll cells is broken down in the bundle, sheath cells to release CO2 . This results in increasing the, intracellular concentration of CO2 ., In turn, this ensures that the RuBisCO functions as a, carboxylase, minimising the oxygenase activity., The C 4 -plants lack photorespiration, that is why the, productivity and fields are better in these plants., l, , l, , l, , Differences between C 3 and C 4 -Plants, Characteristics, , C3-plants, , C4 -plants, , Cell type in which the, Calvin cycle takes place, , Mesophyll, , Bundle sheath, , Cell type in which initial, carboxylation takes place, , Mesophyll, , Mesophyll, , How many types of cells, does the leaf have that fix, CO2, , 1; mesophyll, , 2; mesophyll and, bundle sheath, , Number of carbons in, primary CO2 acceptor, , 5, , Primary CO2-fixation, product, , 3 Phosphoglyceric Oxaloacetic Acid, Acid (PGA), (OAA), , Numbers of carbons in, primary CO2-fixation, product, , 3, , Presence of RuBisCO, , Yes, , Yes, , Presence of PEPCase, , No, , Yes, , Cells having RuBisCO, , Mesophyll, , Bundle sheath, , 3, , 4, , Factors Affecting, Photosynthesis, The rate of photosynthesis gets affected by many internal and, external or environmental factors., , 1. Internal Factors, These factors include number, size, age and orientation of, leaves, mesophyll cells and chloroplasts, internal, concentration of CO2 and chlorophyll content., , 2. External Factors, These factors generally include an environmental factor like, availability of sunlight, temperature, concentration of CO2, and water., Hence, factors available at suboptimal levels help in, determining the rate of photosynthesis at any point., Concept of Limiting Factors, For a study of the above factors, it is essential to have knowledge of, Blackman's law of limiting factors. This is because before 1905, early, scientists attempted to determine the effect of individual factors on, the photosynthetic rate in terms of minimum, optimum and, maximum values which are known as cardinal points. The, simultaneous effects of other factors, also has an importance in, determining the rate of photosynthesis.

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26, , CBSE Term II Biology XI, , Blackman criticised the above said concept and stated that,, when a process is controlled by more than one factor then the, rate of the process is limited by the factor, which is nearest to its, minimal value (is limited by the pace of the slowest factor)., For example, despite the presence of a green leaf and optimal, light and CO2 conditions, the plant may not photosynthesise till, the moment the temperature is very low. But if the optimal, temperature is provided again to this it will surely start, photosynthesising., Hence, if an increase of light beyond a certain limit or point, occurs it causes the breakdown of chlorophyll and decrease in, the rate of photosynthesis., Some of the factors that affect the photosynthetic rate are, discussed ahead in detail., i. Light, , Rate of photosynthesis, , The light provides the energy for photosynthesis. Thus, it is one, of the major factors, which affect the rate of photosynthesis., Three characteristics of light, i.e. the intensity, quality and, duration generally influences the rate. So, discussing the light as, a factor that affects photosynthesis, two conditions are observed., (a) At low light intensities, the linear relationship between, incident light and rate of CO2 -fixation occurs., (b) While at higher intensity of light, the rate fails to show, further increase as the other factors become limiting, (saturation point)., , B, , E, , C, , A, , ii. Carbon Dioxide Concentration, In C 4 -plants also, the photosynthesis increases as the, CO2 concentration increases, but at much lower, concentration of CO2 , these plants tend to attain, saturation (around 360 µL−1, while the C 3 -plant becomes, saturated at much higher CO2 ) level (around 450 µL−1 )., Thus, it concludes that the current availability of CO2, levels is a limiting factor to the C 3 -plants., It has been demonstrated by the scientists itself that the, C 3 -plants can grow much faster and lead to higher, productivity due to the higher rate of photosynthesis., Thus, in order to obtain higher yield some greenhouse, crops like tomatoes, bell pepper, etc., are allowed to grow, in atmosphere enriched with carbon dioxide., iii. Temperature, Enzyme controlled dark reactions are affected by change, in temperature. Photosynthesis occurs in a very wide, range of temperature. The C 4 -plants respond to a higher, temperature showing higher rate of photosynthesis on the, other hand, the C 3 -plants have much lower optimum, temperature range., When temperature is increased from minimum to, optimum, the rate of photosynthesis doubles for every, 10°C rise in the temperature. But when the temperature, reaches above optimum range the rate of photosynthesis, shows initial increase for a very short duration of time, which later gets declined., Different plants have different optimum temperature, range for photosynthesis. It depends on their habitat. The, tropical plants have higher temperature range for, photosynthesis than the temperature plants., iv. Water, , D, Light intensity, Graph of light intensity on the rate of photosynthesis, , At 10% of full sunlight, the saturation of light occurs. Thus,, excepting the shade and the dense forests, the light is a, limiting factor in a very rare conditions in nature., Note If low light conditions are prevail, both C 3 and C 4 -plants fail to, respond to high CO2 conditions, while at high light intensities, both, show increase in the photosynthetic rates but upto a certain limit., , The effect of water as a factor is more on the plant as a, whole rather than directly on photosynthesis. In water, stress conditions, the stomata become closed which, reduce the availability of CO2 to plants, thereby causing, reduction in the rate of photosynthesis., Besides this the decrease in water availability causes, leaves to wilt thus, reducing the surface area of the leaves, ultimately reducing their metabolic activity.

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27, , CBSE Term II Biology XI, , Chapter, Practice, PART 1, Objective Questions, l, , 4. Match the following columns., Column I, , Column II, , Multiple Choice Questions, , A. Chlorophyll-a 1. Yellow, , 1. Photosynthesis is an essential process for life on, , B. Chlorophyll-b 2. Bright or blue-green, , earth because, (a) it is the primary source of all food on earth, (b) it is responsible for the release of the oxygen, (c) it is the only natural process responsible for the, utilisation of sunlight, (d) All of the above, Ans. (d), , 2. Identify A, B and C in given figure., , C. Xanthophyll, , 3. Yellow or yellow-orange, , D. Carotenoids, , 4. Yellow-green, , Codes, A B C D, (a) 2 4 1 3, (c) 4 3 2 1, Ans. (a) A–2, B–4, C–1, D–3, , A B C D, (b) 3 4 2 1, (d) 4 2 1 3, , 5. Light Harvesting Complexes (LHCs) are, A, B, C, , (a) present within PS-I and PS-II, (b) very few molecule of chlorophyll-a, (c) hundred of pigment molecules bound to proteins, (d) Both (a) and (c), Ans. (d) Both options (a) and (c) are correct., , 6. The movement of electrons in Electron Transport, System (ETS) in light reaction is, (a) A–Stroma wall, B–Granum, C–Stroma, (b) A–Stroma lamella, B–Granum, C–Stroma, (c) A–Stroma lamella, B–Stroma, C–Granum, (d) A–Stroma wall, B–Stroma, C–Granum, Ans. (b) A–Stroma lamella, B–Granum, C–Stroma, , 3. Which one of the following statements is, incorrect about chloroplast ?, (a) Usually chloroplast align themselves along the, walls of mesophyll cells, so that they get optimum, quantity of incident light, (b) Within chloroplast there is a membranous system, consisting of grana, stroma lamellae and stroma, (c) There is division of labour, (d) In grana, CO2 is fixed, Ans. (d) Statement in option (d) is incorrect and can be, corrected as, CO2 is fixed during Calvin cycle in the stroma of, chloroplast., , (a) uphill in terms of redox potential scale, (b) downhill in terms of redox potential scale, (c) uphill in terms of oxidation, (d) Both (a) and (b), Ans. (b) The movement of electrons in ETS in light reaction is, downhill in terms of an oxidation-reduction or redox potential, scale., , 7., , B, , A, e– acceptor, , Light, , C, ADP+iP ATP, , NADPH, NADP+, , Electron, transport, system, , LHC, D, H 2O, , 2e– + 2H+ +[O]

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28, , CBSE Term II Biology XI, , Which of the following is correctly labelled for the, given figure?, (a), (b), (c), (d), , A–PS-II, B–PS-I, C– e − acceptor, D–LHC, A–LHC, B– e − acceptor, C–PS-I, D–PS-II, A–PS-I, B–PS-II, C– e − acceptor, D–LHC, A– e − acceptor, B–LHC, C–PS-II, D–PS-I, , Ans. (c) A–PS-I, B–PS-II, C–e − acceptor, D–Light Harvesting, , Complex (LHC), , 8. Read the following statements., I. The electrons that carryout photophosphorylation, are located in the thylakoid membrane., II. During photophosphorylation, the chloroplast, stroma becomes more acidic than the interior of, thylakoid membrane., III. Protons diffuse through the protein channels, which are ATP synthetase molecules., IV. ATP is formed from ADP + Pi on the stroma side, of the thylakoid in the chloroplast., V. During photophosphorylation, water ionises to, form H + , yielding electrons to PS-II., , Which of the following above statements is/are, false?, (a) I and II, (b) III and IV, (c) IV and V, (d) Only II, Ans. (d) Statement II is false and can be corrected as, During photophosphorylation, the chloroplast stroma is, less acidic than the interior of thylakoid membrane, because accumulation of protons during ETC occurs in, the lumen of thylakoid., Rest given statements are correct., , (a) C3-plants forming PGA and C4 -plants forming OAA,, respectively as first products of CO2-fixation, (b) C3-plants forming OAA and C4 -plants forming PGA,, respectively as first product of CO2-fixation, (c) C3-plants forming PEP and C4 -plants forming OAA,, respectively as first product of CO2-fixation, (d) None of the above, Ans. (a) CO2 assimilation during biosynthetic phase of, photosynthesis was said to be of two main types, i.e., C3-plants in which first stable product of CO2-fixation is, PGA (C3 acid) and C4 -plants in which first stable product, of CO2-fixation is OAA (C4 acid)., , 11. What is the site for C 3 -cycle in C 3 and C 4 -plants?, (a) In C3-plants – Mesophyll cell and in, C4 -plants–Bundle sheath cell, (b) In C3-plants – Bundle sheath cell and in, C4 -plants–Mesophyll cell, (c) In C4 -plants – Bundle sheath cells and in, C3-plants–Bundle sheath cell, (d) In C3-plants – Mesophyll cell and in, C4 -plants–Mesophyll cell, Ans. (a) In C3-plants, all the reactions occur in mesophyll, cells, while C4 -plants show a distinct type of anatomy, called as Kranz anatomy where both mesophyll cells and, bundle sheath cells are involved., , 12. Identify A, B, C and D in the given figure and, choose the correct option accordingly., Atmospheric CO2, Plasma membrane, A, , 9. Consider the following statements., I. During chemiosmotic synthesis of ATP, one ATP, molecule is formed when 2H + pass through, ATPase., II. Light reaction of photosynthesis involve, photochemical reactions., III. Dark reaction of photosynthesis involve carbon, reaction., IV. Splitting of water takes place on the inner surface, of the thylakoid membrane., , Choose the option containing correct statements., (a) I, III and IV, (b) I, II and IV, (c) I, II, III and IV, (d) I, II and III, Ans. (c) All the given statements are correct., , 10. Plants are divided into two groups based on the, pathways they use for CO 2 assimilation during, biosynthetic phase of photosynthesis. These are, , Cell wall, HCO3–, , Plasmodesmata, , Phosphoenolpyruvate, , B, , Regeneration, , C4 acid, , C3 acid, , Transport, , Transport, , C, , Fixation by, Calvin cycle, C4 acid, CO2, D, , C3 acid

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29, , CBSE Term II Biology XI, , (a) A–Mesophyll cell, B–Fixation, C–Bundle sheath cell,, D–Decarboxylation, (b) A–Mesophyll cell, B–Decarboxylation, C–Bundle sheath, cell, D–Fixation, (c) A–Chloroplast, B–Decarboxylation, C–Bundle sheath cell,, D–Fixation, (d) A–Chloroplast, B–Fixation, C–Bundle sheath cell,, D–Fixation, Ans. (a) A–Mesophyll cell, B–Fixation, C–Bundle sheath cell,, D–Decarboxylation, , 13. Which of the following statements regarding, photorespiration is/are true?, (a) It is a metabolically expensive pathway, (b) It is avoided when CO2 is abundant, (c) It results in a loss of usable carbon dioxide, (d) All of the above, Ans. (d) All the given statements are correct regarding, photorespiration., , 14. Match the following columns., Column I, A. Oxygen evolving, complex, B. Proton gradient, C. Hill reaction, D. Photorespiration, , Column II, 1. Potassium ferric oxalate, 2., 3., 4., 5., , High oxygen concentration, ATP synthesis, Pheophytin, Photolysis of water, , Codes, A B C D, (a) 5 3 1 2, (b) 1 2 4 5, (c) 5 1 4 2, (d) 3 4 5 1, Ans. (a) A–5, B–3, C–1, D–2, , 15. Plant factors affecting photosynthesis include, (a) number, age, size and orientation of leaves, mesophyll, cells and chloroplast, internal CO2 concentration and the, amount of chlorophyll, (b) nature of leaves, size of mesophyll cell and light, (c) mesophyll cells distribution and temperature, (d) quantity of chlorophyll, size of leaves and CO2, Ans. (a) The rate of photosynthesis is important in determining the, yield of plants including crop plants. Photosynthesis is under, the influence of several factors, both internal (plant) and, external. The plant factors include the number, size, age and, orientation of leaves, mesophyll cells and chloroplast,, internal CO2 and O2 concentration and the amount of, chlorophyll., , l, , Assertion-Reasoning MCQs, Direction (Q. Nos. 1-5) Each of these questions, contains two statements, Assertion (A) and, Reason (R). Each of these questions also has four, alternative choices, any one of which is the, correct answer. You have to select one of the, codes (a), (b), (c) and (d) given below., (a) Both A and R are true and R is the correct, explanation of A, (b) Both A and R are true, but R is not the correct, explanation of A, (c) A is true, but R is false, (d) A is false, but R is true, , 1. Assertion (A) During photosynthesis, glucose is, formed, but it is stored in the form of starch., Reason (R) Glucose is osmotically active, while, starch is inactive., Ans. (a) Both A and R are true and R is the correct, , explanation of A., , 2. Assertion (A) PS-I and PS-II names are given on, the basis of activity in the photosynthesis., Reason (R) During non-cyclic, photophosphorylation, PS-II works first and, then PS-I., Ans. (d) A is false, but R is true. A can be corrected as, , The photosystem-I and photosystem-II are named in, the sequence of their discovery and not in the, sequence in which they function during the light, reaction. During non-cyclic photophosphorylation,, PS-II works first and then PS-I., , 3. Assertion (A) Non-cyclic photophosphorylation, occurs in the granum of chloroplasts., Reason (R) There is discontinuous flow of, electrons in this process., Ans. (c) A is true, but R is false because, , Non-cyclic photophosphorylation occurs in granum of, chloroplast. It is an association of photosystems-I and, II., In this process, electrons continuously flow from, water to PS-II then to PS-I and then finally to, NADH., , 4. Assertion (A) In C 3 -cycle, the first stable, compound is 3C compound., Reason (R) In C 4 -plants, Calvin cycle is absent.

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30, , CBSE Term II Biology XI, , Ans. (c) A is true, but R is false because, , In C3-cycle, the first stable compound is 3C compound,, the phosphoglycerate which is formed by the, carboxylation of RuBP by one molecule of CO2 in the, presence of RuBP carboxylase., In C4 -plants the first CO2-fixation product is a 4C, oxaloacetic acid, but they use C3-pathway or Calvin, cycle as the main biosynthetic pathway for carbon, fixation (carboxylation), which occurs in the bundle, sheath cells of leaves., , 5. Assertion (A) Photorespiration is a waste process., Reason (R) During photorespiration, neither ATP, nor NADPH is formed., Ans. (a) Both A and R are true and R is the correct, , explanation of A., l, , Case Based MCQ, Direction Read the following passage and answer, the questions that follows., During photosynthesis, light energy is converted, into chemical energy in a multiprotein complex, called photosystem. The thylakoid membrane, contains two types of photosystems, viz., PS-I and, PS-II and each of them consists of multiple, antenna proteins containing chlorophyll, molecules and other pigments. These pigments, absorb light energy, so that the photosystems can, carryout light-dependent or independent, reactions., (i) The products of light-dependent reactions are, , (a) CO 2 and ATP, (b) NADPH, ATP and CO 2, (c) O 2, ATP and NADPH, (d) O 2 and FADH 2, Ans. (c) The products of light-dependent reactions are oxygen, (O 2), ATP and NADPH., , (ii) PS-I functions when, (a) wavelength of light is higher than 680 nm, (b) NADPH accumulates, (c) CO 2-fixation is retarded, (d) All of the above, Ans. (d) All the listed factors are required for the functioning of, PS-I., , (iii) PS-II transfers its electrons to, (a) chloroplast, (b) mitochondria, (c) PS-I, (d) None of these, Ans. (c) PS-II has the reaction centre of P680. It absorbs light, energy and passes its electrons to the PS-I., , (iv) In PS-I, electrons come from, (a) splitting of water, (b) ETC, (c) mitochondria, (d) Either (a) or (b), Ans. (b) In PS-I, electrons are derived from the Electron, Transport Chain (ETC)., , (v), , e– acceptor ATP, , A, , e– acceptor, , B, , NADP+ → NADPH, , Identify the correct description about given diagram., I. A and B represent P700 and P680, respectively., II. Given process depicts oxidation/reduction changes, during the light reaction of photosynthesis., III. The given process was discovered by Bendall and, Hill in 1960., Choose the correct option., (a) I, II and III, (b) I and II, (c) II and III, (d) I and III, Ans. (c) II and III are correct and I is incorrect. It can be, corrected as, A and B represent P680 and P700, respectively.

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31, , CBSE Term II Biology XI, , PART 2, Subjective Questions, l, , Short Answer (SA) Type Questions, 1. Mention any two reasons, which prove that, , photosynthesis is essential for sustaining life on, the earth., Ans Two reasons are as follows, (i) It is the process by which food is manufactured for, all living organisms., (ii) It is the only natural process by which oxygen is, liberated into the atmosphere. This O2 is used by, all living organisms respiring aerobically., , 2. In tropical rainforests, the canopy is thick and, shorter plants growing below it, receive filtered, light. How are they able to carry out, photosynthesis?, Ans The plant carry out photosynthesis in the presence of, , light. The light transmitted through the tree canopy is of, low intensity light. Therefore, plants growing under the, canopy of others have adapted themselves to carryout, photosynthesis in low light intensities. The rate could be, different depending upon the intensity and quantity of, light received., , 3. Explain the reasons of following, (i) Photosynthesis can occur in the absence of light., (ii) Even non-green leaves can make the food., (iii) Photosynthesis can occur under water., Ans, , (i) Photosynthesis cannot occur in the absence of, sunlight. The sunlight originally supplies the, energy for conversion of CO2 to carbohydrate., (ii) Yes, the chlorophyll is the most prominent plant, pigment, but not in all plants. Some other accessory, pigments such as xanthophylls and carotenoids can, also perform photosynthesis separately (in some, algae)., (iii) Photosynthesis can occur under water only when, the water is clear and shallow. Some alga, (Rhodophyta) can synthesise food at deep water, layers as they can absorb the light of blue wavelength,, efficiently., , 4. Cyanobacteria and some other photosynthetic, bacteria do not have chloroplasts. How do they, conduct photosynthesis?, (NCERT Exemplar), Ans. The cyanobacteria and photosynthetic bacteria are, , prokaryotes. They do not have well defined membrane, bound cell organelles but these organisms have, photosynthetic pigments in a membranous form, which, are primitive in nature but can trap and use solar energy., Their photosynthetic lamellae are suspended freely in, the cytoplasm. So, they can carry out photosynthesis., , 5. Describe how Engelmann arrived at the first action, spectrum of photosynthesis., Ans. TW Engelmann performed an interesting experiment with, , green alga, Cladophora. He splitted light into its spectral, components by using prism. He then illuminated the alga, placed in a suspension of aerobic bacteria Rhodospirillum., He noticed that the accumulation of bacteria was mainly in, the region of the blue and red light of the split spectrum., By the work done by him at first, action spectrum of, photosynthesis was thus described, which roughly, resembles the absorption spectra of chlorophyll-a and b., , 6. Differentiate between stroma and grana of, chloroplasts., Ans. Differences between stroma and grana of chloroplasts are, , as follows, Stroma, , Grana, , It is the jelly-like matrix of the, chloroplast., , These are formed of stacks, of thylakoids., , Dark reaction takes place here. Light reaction takes place, here., , 7. If a green plant is kept in dark with proper, ventilation, can this plant carryout photosynthesis?, Can anything be given as supplement to maintain its, growth or survival?, (NCERT Exemplar), Ans. Plants need sunlight for photosynthesis. The sun is the, , only thing that will help plants make their own food. If, there is a small opening in the room that let in sunlight, however, the plant would grow towards the opening or the, light to carryout photosynthesis and will survive., , 8. Why is the colour of a leaf kept in the dark, frequently becomes yellow or pale green? Which, pigment do you think is more stable?, (NCERT), Ans. Since leaves require light to perform photosynthesis the, , colour of a leaf kept in the dark changes from a darker to a, lighter shade of green. Some time it also turns yellow., This is due to the disintegration of chlorophyll pigment in, continuous absence of light., During this process, the xanthophyll and carotenoid, pigments become predominant, causing the leaf to become, yellow. These pigments are more stable as light is not, essential for their production., , 9. Give reasons for the following., (i) Plants are the lungs of nature., (ii) Chlorophyll-b and other accessory pigments are, necessary for photosynthesis., (iii) In the high light intensities, the chlorophyll-a gets, damaged.

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32, Ans., , CBSE Term II Biology XI, , (i) Plants are also called lungs of the nature because,, they perform the exact function as lungs do in, mammals. They produce oxygen, which is necessary, for all forms of life. So, in essence since our lungs, keep us alive in the same way the trees keep our, lungs alive. Thus, they are considered to be the part, of our lung existence., (ii) Chlorophyll-b and other accessory pigments are, necessary as these are light absorbing compounds, found in photosynthetic organisms. These pigments, enable a wider range of wavelength of incoming, light to be utilised for photosynthesis., (iii) Chlorophyll-a structure is such that it gets damaged, by bright/high light intensities. It is protected by, carotenoid pigments., , 10. Examine the figure, , 12. Suppose there were plants that had a high, concentration of chlorophyll-b, but lacked, chlorophyll-a, would it carry out photosynthesis? Also, mention why do plants have chlorophyll-b and other, accessory pigments?, (NCERT), Ans. Though chlorophyll-a is the major pigment responsible for, , trapping light. They act as antenna molecules and forms, the reaction centres for both photosystems-I and II. Other, photosynthetic pigments like chlorophyll-b, xanthophylls, and carotenoids, which are called accessory pigments, also, absorb light of different energy wavelengths and transfer, their energy to chlorophyll-a. Indeed, they not only enable, a wider range of wavelength of incoming light to be, utilised for photosynthesis, but carotene protects, chlorophyll-a from photo-oxidation. If any plant lack, chlorophyll-a and contain a high concentration of, chlorophyll-b, then this plant would not undergo, photosynthesis., , 13. Chlorophyll-a is the primary pigment for the light, reaction. What are accessory pigments? What is, their role in photosynthesis?, Ans. Accessory pigments are also photosynthetic pigments., , (i) This structure is present in animal cell or plant, cell?, (ii) Can these be passed on to the progeny? How?, (iii) Name the metabolic processes taking place in the, places marked A and B., (NCERT Exemplar), Ans., , (i) This structure present in plant cell., (ii) Yes, these can be passed on to the progeny through, female gametes., (iii) In part A photophosphorylation and in part, B Calvin cycle take place., , 11. Which property of the pigment is responsible for, its ability to initiate the process of photosynthesis?, Why is the rate of photosynthesis higher in the red, and blue regions of the spectrum of light?, Ans. The chlorophyll pigments are present in the thylakoid, , membranes. They have the property of excitability and, emits e − in the excited stage, though this e − is replaced, and transferred by the e − generated from splitting of, water molecules., Red and blue light have maximum energy which a, chlorophyll pigment absorbs and get excited and initiate, the process of photosynthesis., Also, its wavelength are 400-700 nm, i.e. between the, Photosynthetic Active Radiation (PAR). Thus, the rate of, photosynthesis is higher in blue and red light., , These are chlorophyll-b, xanthophyll and carotenoids., These are not directly involved in emission of excited, electrons, but they help in harvesting solar radiation and, pass it on to chlorophyll- a., This pigment itself absorbs maximum radiation at blue and, red region. So, chlorophyll-a is the chief pigment of, photosynthesis and others (i.e. chlorophyll-b, xanthophyll, and carotenoids) are accessory pigments., , 14. How are photosynthesis and respiration related to, each other?, Ans. Photosynthesis and respiration are related, as in both, , mechanisms, the plants gain energy. In photosynthesis,, plants gain energy from solar radiations whereas, in, respiration, they breakdown glucose molecule to get, energy in the form of ATP molecules., They are related also because they are dependent on each, other. The product of photosynthesis, i.e. glucose (food) is, utilised in respiration to yield energy (ATP)., While doing so, it releases many other simple molecules, (CO2 + H 2O) which are utilised in photosynthesis to, produce more sugars., , 15. What can we conclude from the statement that the, action and absorption spectra of photosynthesis, overlap? At which wavelength, do they show peaks?, (NCERT Exemplar), Ans. The absorption spectrum is the graph plotted, with the, , amount of light absorbed as a function of wavelength. The

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33, , CBSE Term II Biology XI, , 16. 2H2O → 2H + + 4e − + O 2 ↑, , 21. In the diagram shown below labels A, B and C., What type of phosphorylation is possible in this?, Photosystem-I, , Based on the above equation, answer the following, questions, (i) Where does this reaction take place in plants?, (ii) What is the significance of this reaction?, Ans., , (i) Lumen of the thylakoids., (ii) O2 is evolved during this reaction, moreover, electrons are made available to PS-II continuously., , 17. Name the end products of light reaction of, photosynthesis. Mention the fate of each of them., Ans. ATP, NADPH and oxygen are the end products of light, , reaction., ATP and NADPH are used in the reduction step of, biosynthetic phase of photosynthesis. Oxygen is liberated, into the atmosphere., , 18. What are the important events and end products of, the light reaction?, Ans. The important events of light reactions are, , (i) Excitation of chlorophyll molecule to emit a pair of, electrons and use of their energy in the formation of, ATP from ADP + Pi. This process is called, photophosphorylation., (ii) Splitting of water molecule, (a) 2H 2O → 4H + + 4 e – + O2 ↑, (a) NADP + 2 H+ → NADPH 2, End products of light reaction are NADPH and ATP., Reducing power is produced in the light reaction, i.e., ATP and NADPH 2 molecules, which are used up in, dark reaction. O2 is evolved as a byproduct by the, splitting of water., , 19. Dark reactions are dependent on light yet are, called dark reactions. Justify., Ans. Dark reactions are dependent on light but not directly, , rather it is dependent on the products of light reaction, that are ATP and NADPH to carryout reduction of CO2, to form glucose. This does not need light so, these are, called dark reactions., , 20. Cyclic photophosphorylation results in the, production of ATPs and not NADPH. Give reasons., Ans. Cyclic phosphorylation occurs when only 700 nm light is, , available and PS-I is functional. It occurs in the stroma, lamellae where enzyme NADP reductase is absent and, PS-II is also absent. Hence, electrons are passed on back, to PS-I and not to NADP + . So, the cyclic flow results in, the formation of ATP, but not NADPH., , A, , ATP, Light, , ADP, +iP, , action spectrum is the graph plotted with the rate of, photosynthesis as a function of wavelength. Since, the, amount of light absorbed and the rate of photosynthesis, have a direct relationship, the two curves overlap. They, show peaks around wavelengths 450 nm (blue region), and 650-680 nm (red region)., , B, , C, , Ans. The diagram is showing cyclic photophosphorylation., , Here, A is electron acceptor, B is electron transport, system and C is photosystem-I or PS700., In cyclic photophosphorylation, only PS-I is functional., The electron is circulated within the photosystem and the, phosphorylation occurs due to cyclic flow of electrons., , 22. Why is the lumen of thylakoids acidic while, the, stroma is alkaline in nature?, Ans. The acidic nature of lumen of thylakoids is due to the, , accumulation of protons by the photolysis of water. The, same reaction does not occur in stroma so, it is basic in, nature., , 23. Mention the four basic requirements for, chemiosmosis to occur., Ans. Four basic requirements are as follows, , (i) A unit membrane, (iii) A proton gradient, , (ii) A proton pump, (iv) ATP synthase enzyme, , 24. Expand RuBP and also mention the role of RuBP in, photosynthesis., Ans. RuBP is known as Ribulose 1, 5-Bisphosphate. It is the, , primary acceptor of carbon dioxide in Calvin cycle of, C3-plants. It forms the first stable compound of, photosynthesis known as PGA., , 25. ATPase enzyme consists of two parts. What are, those parts? How are they arranged in the thylakoid, membrane., The conformational changes occur in which part of, the enzyme?, Ans. ATPase enzyme consists of two parts, i.e. a stalk (F0 ) and a, , headpiece (F1 ). These two parts are located completely, across the membrane of thylakoid. The conformational, changes occur in the headpiece (F1 ) of this enzyme., , 26. Explain how during light reaction of photosynthesis,, ATP synthesis as a chemiosmotic phenomenon takes, place?, Ans. Chemiosmosis required a membrane, a proton pump, a, , proton gradient and ATP synthase enzyme. Energy is used, to pump protons across a membrane, to create a gradient, or a high concentration of protons within the thylakoid, lumen. ATP synthase enzyme catalyses the formation of

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34, , CBSE Term II Biology XI, , ATP, along with the NADPH produced by the movement, of electrons. The energy carried by ATP molecules will be, used immediately in the biosynthetic reaction taking, place in the stroma for fixing CO 2 and synthesis of sugars., , 27. Where is NADP reductase enzyme located in the, chloroplasts? What is the role of this enzyme in, proton gradient development?, (NCERT Exemplar), Ans. NADP reductase enzyme is located on the outer/stroma, , side of the thylakoid membrane. Along with the electrons, from the primary acceptor of PS-I, it uses the protons of, stroma for the reduction of NADP + to NADPH. This, removal of protons from the stroma causes a proton, gradient between the lumen of thylakoids and the stroma., , 28. The diagram given below shows stages in the, light-independent reactions of photosynthesis., Answer the following, (i) At which stage NADPH is oxidised?, (ii) What are A, B and C ?, (iii) At what stages ATP is converted into ADP?, CO2, Carboxylation, ADP, Enzyme A, , 3-phosphoglyceric acid, D, , 1, 3-bisphosphoglyceric acid, , Ribulose-1, 5-bisphosphate, , cells where the enzyme, RuBisCO and other Calvin cycle, enzymes are located and where CO2 released by, decarboxylation of the 4 carbon acids is then fixed by, RuBisCO enzyme to form 3-phosphoglyceric acids (3C)., The physical separation of RuBisCO from the oxygen, driven light reactions inhibits photorespiration and, increases CO2-fixation. This way photosynthetic capacity, of the C4 -plants increases many folds than C2-plants., , 30. What is the basis for designating C 3 and C 4, pathways of photosynthesis?, Ans. C3-pathway or Calvin cycle represents phase-II, i.e., , dark reaction of photosynthesis. In Calvin cycle, a 5C, pentose sugar, Ribulose Bisphosphate (RuBP) acts as first, acceptor of CO2 whereas, the C4 -pathway is also called, Hatch-Slack pathway in which, the first CO2 acceptor is, 3C Phosphoenol Pyruvate (PEP)., , 31. By looking at a plant externally, can you tell, whether it is C 3 or C 4 ? Why and how?, Ans. The plants which are adapted to dry tropical regions have, , the C4 -pathway. However, the C4 -plants do not show any, characteristic in external morphology. Unlike C3-plants,, the leaves of C4 -plants have a special anatomy called, Kranz anatomy and this difference can only be observed, at the cellular level. Therefore, it is difficult to say, whether a plant is C3 or C4 by looking it only externally., , 32. Give comparison between the C 3 leaf anatomy and, C 4 leaf anatomy., Ans. Comparison between anatomy of leaves in C3 and, , F, , B, , Ribulose-5-phosphate, E, , C, , C4 -plants are given below, C3 Leaf Anatomy, , C4 Leaf Anatomy, , Only one type of, chloroplast is present., , Kranz anatomy, i.e. type of, cell, each with its own type, of chloroplast is present., , Less efficient in, photosynthesis than C 4, leaves., , More efficient in, photosynthesis than C 3, leaves., , Only mesophyll cells, carryout photosynthesis., , Both mesophyll cells and, bundle sheath cells, carryout photosynthesis., , C, Hexose, , Ans., , (i) NADPH is oxidised at stage E., (ii) A–RuBP carboxylase oxygenase (RuBisCO),, B–Reduction, C–Regeneration, (iii) ATP is converted to ADP at stages D and F., , 29. Even though a very few cells in a C 4 -plant carry, out the biosynthetic Calvin pathway, yet they are, highly productive. Can you discuss why?, Ans. C 4 -plants chemically fix carbon dioxide in the cells of the, , mesophyll by adding it to the 3 molecules of Phosphoenol, Pyruvate (PEP), a reaction catalysed by an enzyme called, PEP carboxylase. It creates the 4 carbon organic acid,, oxaloacetic acid. Oxaloacetic acid synthesised by this, process is then translocated to specialised bundle sheath, , 33. What conditions enable RuBisCO to function as an, oxygenase? Explain the ensuring process., Ans. RuBisCO possess an affinity for carbon dioxide and, , oxygen. In the presence of high carbon dioxide, concentration the enzyme would effectively results in the, formation of carboxylase. But in the presence of high, concentration of oxygen, the enzyme would react and, form oxygenase. This forces CO2 to enter C2-cycle, thus, leading to photorespiration and loss of CO2.

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35, , CBSE Term II Biology XI, , 38. Which of the following would not be a limiting, , 34. Why is RuBisCO enzyme the most abundant, enzyme in the world?, , factor in photosynthesis? Explain giving example., , Ans. The enzyme Ribulose-1, 5-bisphosphate carboxylase, , oxygenase, most commonly known by the shorter name, RuBisCO is used in the Calvin cycle of photosynthesis to, catalyse the first major step of carbon-fixation., RuBisCO is thought to be the most abundant protein in, the world since it is present in every plant that performs, photosynthesis., It makes about 20-25% of the soluble protein in the, leaves and is made on the earth at the rate of about, 1000 kg/s. It is estimated that every person on earth is, supported by about 44 kg of RuBisCO., , (i) CO2, (ii) Oxygen, (iii) Light, (iv) Chlorophyll, Ans. (iv) Chlorophyll would not act as a limiting factor in, photosynthesis, e.g. sunloving plants contain less, chlorophyll as compared to shadeloving plants, but the, rate of photosynthesis in bright light is much higher in, sunloving plants than is shadeloving plants., , 39. Some of these terms/chemicals are associated with, the C 4 -cycle. Explain., (i) Hatch-Slack pathway, (ii) Calvin cycle, (iii) PEP carboxylase, (iv) Bundle sheath cells, , 35. In what kind of plants do you come across Kranz, anatomy? To which conditions are those plants, better adapted? How are these plants better, adapted than the plants, which lack this anatomy?, , (NCERT Exemplar), Ans. The terms associated with C4 -cycle are, , Ans. C4 -plants are better adapted to dry tropical regions., , (i) Hatch-Slack Pathway The process of synthesis of, glucose in C4 -plants is different from C3-plants which, was discovered by two scientists MD Hatch and CR, Slack (1977). Hence, named Hatch-Slack pathway., (ii) Calvin Cycle This cycle operates in bundle sheath cells, and fixes CO2 to form glucose molecules., (iii) PEP Carboxylase It is an enzyme present in mesophyll, cells of C4 -plants. It fixes CO2 to form 4-carbon, compound, i.e. Oxalo Acetic Acid (OAA)., (iv) Bundle Sheath Cells These are specialised, sclerenchymatous cells present around the vascular, bundle, in the veins of monocot leaves. These have, agranal chloroplast. C3-cycle occurs in these cells to, manufacture glucose in C4 -plants., , They have the following features, (i) Can tolerate high temperatures., (ii) Can perform photosynthesis in high light intensities., (iii) Have overcome the problem of photorespiration and, have greater productivity of biomass., , 36. Fill in the blanks at A, B, C, D, E and F and, complete the C 4 -pathway/Hatch-Slack pathway., Atmospheric CO2 enters A, , ↓, CO2 is accepted by B and forms four carbon acid compound C, , ↓, C 4 acid enters into D and splits into CO2 and E, , ↓, CO2 enters Calvin cycle and 3C acid F is formed, Ans. A–Mesophyll cell, B–Phosphoenol Pyruvate (PEP),, , C–Oxaloacetic Acid (OAA), D–Bundle sheath cells,, E–Pyruvate, F–Phosphoglyceric Acid (PGA)., , 37. A group of plants lacks photorespiration. Answer the, following questions based on these plants., (i) Which cells in the plant have RuBisCO?, (ii) Does photorespiration occur in these plants?, (iii) In which cells the CO2 -fixation initially occurs?, Ans., , (i) Bundle sheath cells in the plant have RuBisCO., (ii) Photorespiration does not occur in these plants., (iii) Atmospheric CO2 is first fixed into organic acid (4C), in the mesophyll cells in the presence of PEP, carboxylase enzyme., , l, , Long Answer (LA) Type Questions, 1. Is it correct to say that photosynthesis occurs only, in leaves of a plant? Besides leaves, what are the, other parts that may be capable of carrying out, photosynthesis? Justify., , Ans. Although all cells in the green part of a plant have, , chloroplasts, most of the energy is captured in the leaves., The cells in the interior tissues of a leaf, called the, mesophyll, can contain between 450000 and 800000, chloroplasts for every square millimeter of leaf, (nearly 60-70 chloroplasts/cell)., The surface of the leaf is uniformly coated with a, water-resistant waxy cuticle that protects the leaf from, excessive evaporation of water and decreases the, absorption of ultraviolet or blue light to reduce heating., The transparent epidermal layer allows light to pass, through to the palisade mesophyll cells, where most of, the photosynthesis takes place., The green stems are also capable of performing, photosynthesis.

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36, , CBSE Term II Biology XI, , 2. Reduction After the carboxylation reaction,, reduction of PGA takes place through a series of, reactions leading to the formation of glucose. In this, step, the ATP (as energy source) and NADPH, (hydrogen atom carrier) are utilised. It is to be noted, that 2 molecules of ATP and 2 molecules of NADPH, are utilised in this step for phosphorylation and for, the reduction of CO2, respectively., Hence, the fixation of 6 molecules of CO2 and 6, turns of the cycle are required in order to release, one molecule of glucose from the pathway., 3. Regeneration For the continuous and uninterrupted, functioning of the Calvin cycle, there must be a, regular supply of ATP, NADPH and also sufficient, amount of RuBP is required. The regeneration of, RuBP (CO2 acceptor) is a complex process and, involves many types of sugar starting from triose (3C), to heptose (7C)., The regeneration step requires one ATP molecule, for phosphorylation. Hence, for every CO2 molecule, that enters the Calvin cycle, are required 3, molecules of ATP and 2 molecules of NADPH., , 2. The entire process of photosynthesis consists of a, number of reactions. Name the part of the cell, where following reactions take place., (i) Synthesis of ATP and NADPH ................. ., (ii) Photolysis of water ................... ., (iii) Fixation of CO2 ................... ., (iv) Synthesis of sugar molecule .................... ., (v) Synthesis of starch ................... ., Ans., , (i) Synthesis of ATP and NADPH in thylakoids., (ii) Photolysis of water occurs in inner side of thylakoid, membrane in PS-II (680 nm)., (iii) Fixation of CO2 occurs in stroma of chloroplast., (iv) Synthesis of sugar molecule occurs in chloroplast., (v) Synthesis of starch occurs in cytoplasm., , 3. Give comparison between the cyclic and non-cyclic, photophosphorylation., , [NCERT], , Ans. Comparison between cyclic and non-cyclic, , photophosphorylation are as follows, Cyclic, Photophosphorylation, , Non-cyclic, Photophosphorylation, , It occurs in photosystem-I in It is carried out by both PS-I, stromal or intergranal, and PS-II in the granal, lamellae., thylakoids., It is not connected to, photolysis of water so no, oxygen is evolved., , It is connected with, photolysis of water, so oxygen, is evolved in it., , It is activated by light of, 700 nm wavelength., , It occurs in 680 nm as well as, 700 nm wavelength., , It generates ATP only, there It produces both ATP as well, is no formation of NADPH 2. as NADPH 2., Chlorophyll does not receive The source of electrons is, any electron from donor., photolysis of water., The system does not take, This system is connected with, part in photosynthesis except CO2-fixation and is dominant, in bacteria., in green plants., , 4. Where does Calvin cycle take place in chloroplasts?, Describe the three phases of Calvin cycle?, Ans. Calvin cycle occurs in bundle sheath cell of the, , chloroplast., Calvin or C3-cycle has many steps which are known as, glycotic reversal or formation of sugar and takes place, between reduction and regeneration. There are three, major steps as follows, 1. Carboxylation It is the most crucial step of the Calvin, cycle. In this fixation of CO2 molecule takes place in the, form of carboxylation of RuBP (5C). This reaction is, catalysed by the enzyme RuBP carboxylase. This, finally leads to the formation of two molecules of, 3 Phosphoglyceric Acid (3PGA). As the RuBP, carboxylase enzyme also has an activity of, oxygenation., , 5. A cyclic process is occurring in C 3 -plant, which is, light dependent and needs O 2 . This process does, not produce energy rather it consumes energy., (i) Can you name the given process?, (ii) Is it essential for survival of the plant?, (iii) What are the end products of this process?, (iv) Where does it occur?, (v) Does it occur in C 4 -plants also?, Ans., , (i), (ii), (iii), (iv), , Photorespiration., No, it is not essential for survival of the plant., Hydrogen peroxide., The photorespiration occurs in chloroplast,, peroxisomes and mitochondria., (v) No, it does not occur in C4 -plants., , 6. What special anatomical features are displayed by, leaves of C 4 -plants? How do they provide, advantage over the structure of C 3 -plants?, Ans. C4 -plants are special as they have a special type of leaf, , anatomy (Kranz anatomy) that can tolerate high, temperatures and show a response to high intensities. Inspite, of having Oxaloacetic Acid (OAA) as their first CO2-fixation, product, they use C3-pathway or the Calvin cycle as the main, photosynthetic pathway., According to the structural leaf anatomy of C3 and, C4 - plants, the leaves of C3-plants show only one type of, cells called mesophyll cells, which contain only mesophyll, chloroplast, while leaves of C4 -plants show two types of, cells, i.e. outer mesophyll cells and inner spongy (which, are large) cells around the vascular bundles called bundle, sheath cells arranged in a circular manner., It refers to the presence of two types of the chloroplast in, the leaves. The mesophyll cells contain well-developed

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37, , CBSE Term II Biology XI, , granal chloroplast. They actively participate in light, reaction. These produce ATP and NADPH 2., The rudimentary chloroplasts are present in the cells of, bundle sheath. They are agranal. The bundle sheath cells are, mainly meant to carryout C3-cycle., This does not require well-developed chloroplast so, they, are rudimentary lamellar type., , Ans., , Vascular bundle, Bundle sheath cell, Vascular bundle, Chloroplast, Mesophyll cell, Lower epidermis, Stroma, , TS of maize leaf showing Kranz anatomy, , The bundle sheath cells tend to form several layers around, the vascular bundles., They possess several special features such as, Have large number of chloroplast., Thick walls which are impervious to gaseous exchange., There are no intercellular spaces., l, , l, , l, , 7. RuBisCO is an enzyme that acts both as a carboxylase, and oxygenase. Why do you think RuBisCO carries, out more carboxylation in C 4 -plants?, (NCERT), Ans. RuBisCO has a much greater affinity for CO2 than for O2, , under normal conditions. It is the relative concentration of, O2 and CO2 that determines which of the two will bind to, the enzyme. In C3-plants some O2 does bind to RuBisCO, and hence, CO2-fixation is decreased. Here, the RuBP, instead of being converted to 2 molecules of PGA binds, with O2 to form one molecule and phosphoglycolate in a, pathway called photorespiration. In the photorespiratory, pathway, there is neither synthesis of sugars, nor of ATP,, rather it results in the release of CO2 with the utilisation of, ATP. In the photorespiratory pathway, there is no synthesis, of ATP or NADPH. Therefore, photorespiration is a, wasteful process., In C4 -plants, photorespiration does not occur. This is, because they have a mechanism that increases the, concentration of CO2 at the enzyme site. This takes place, when the C4 acid from the mesophyll is broken down in the, bundle cells to release CO2, this results in increasing the, intracellular concentration of CO2. In turn, this ensures, that the RuBisCO functions as a carboxylase minimising the, oxygenase activity., , 8. Suppose Euphorbia and maize are grown in the, tropical area., (i) Which one of them do you think will be able to, survive under such conditions?, (ii) Which one of them is more efficient in terms of, photosynthetic activity?, (iii) What differences do you think are there in their leaf, anatomy?, , l, , (i) Euphorbia will be able to survive under such, conditions., (ii) Maize is more efficient in terms of photosynthetic, activity., (iii) The maize in a C4 -plant having Kranz anatomy, type of leaf anatomy. The bundle sheath cells are, characterised by having a large number of, chloroplasts, thick walls impervious to gaseous, exchange and no intercellular spaces. While,, Euphorbia, which undergoes CAM (Crassulacean, Acid Metabolism) both pathways occur in, mesophyll cells only they do not have Kranz, anatomy. Also their stomata remain closed during, the day., , Case Based Questions, 1. Direction Read the following passage and answer, the questions that follows., Vidhi attended the guest lecture on, photosynthesis with her biology teacher. Guest for, the seminar explained the basic functioning of, chloroplast in the photosynthetic processes. As, students from different schools attended the, seminar. The guest for the lecture asked all, students to put forward their queries regarding, the topic. Vidhi stood up and asked him that, she, is unable to understand the division of labour in, the chloroplast. He appreciated her doubts and, explained her about the same., (i) What do you understand by the division of labour, in chloroplast?, , Ans. Division of labour appears clearly in the chloroplast, i.e., , the membrane system is responsible for the synthesis of, ATP and NADH. The dark reactions, i.e. reduction of, CO2 into carbohydrates and formation of sugar occur in, the stroma of chloroplasts, where enzymes are present., , (ii) How the different pigments are involved in, photosynthesis?, Ans. Various pigments are involved in photosynthesis like, , chlorophyll-a which acts as a chief pigment in, photosynthesis and other pigments like chlorophyll-b,, xanthophyll and carotenoids absorb light and transfer, energy to chlorophyll-a. These pigments other than, chlorophyll-a are called accessory pigments., This pigment enable a wider range of wavelength of, incoming light to be utilised for photosynthesis., , (iii) What is the significance of photosynthesis for, animals?, Ans. The food in the form of starch is stored by plants in, , their parts like fruits, seeds, roots, stems and leaves, etc., All the animals depend on these plant products directly, or indirectly. Hence, the photosynthesis in plants is, very important for sustenance of all forms of life on, earth.

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38, , CBSE Term II Biology XI, , (iv) Oxygen evolved during photosynthesis comes from, H 2 O or CO 2 ?, Ans. Oxygen in photosynthesis evolves from H 2O (i.e. by, , splitting of water) during light reaction., , (v) Photosynthetic pigments are located in which part, of the chloroplast?, Ans. Photosynthetic pigments are located in the thylakoid, , membrane of the chloroplast., , 2. In the figure given below, the black line (upper), indicates action spectrum for photosynthesis and, the lighter line (lower) indicates the absorption, spectrum of chlorophyll-a, answer the following., (NCERT Exemplar), , the fact that immediately after light becomes, unavailable, the biosynthetic phase continues for, some time and then stops; if light becomes available, again, the process continues., Her brother, student of class XI was also listening, the same and was remembering that he had listened, the same from his biology teacher also. He, interupped her sister and asked her to re-explain, the whole process for the better understanding., (i) What are the products of light reaction?, Ans. Oxygen, ATP and NADPH are the products of light, , reaction., , (ii) Can we say that calling the biosynthetic phase,, dark reaction is a misnomer? Justify., Ans. Yes, calling biosynthetic phase a dark reaction is, , misnomer. This phase is not directly dependent on light,, though it depends on the products of light reaction. It, continues for some time, but when light becomes, unavailable then it stops., , (iii) Name the first stable product of photosynthesis., Ans. 3-Phosphoglyceric Acid (PGA) in C3-plants and, Wavelength of light in nm, , (i) What does the action spectrum indicate?, Ans. It is the relative rates of photosynthesis at different, , wavelengths of light., , (ii) How can we derive an absorption spectrum for any, substance?, Ans. Absorption of different wavelengths of light by a, , particular pigment is plotted and is called the absorption, spectrum of that pigment., , (iii) If chlorophyll-a is responsible for light reaction of, photosynthesis, why do the action spectrum and, absorption spectrum not overlap?, Ans. Chlorophyll-a is responsible for light reaction of, , photosynthesis, but the action spectrum and absorption, spectrum do not overlap because, though chlorophyll is, the main pigment responsible for absorption of light,, other thylakoid pigments like chlorophyll-b, xanthophylls, and carotenoids, which are called accessory pigments,, also absorb and transfer the energy to chlorophyll-a., Indeed they not only enable a wider range of wavelength, of incoming light to be utilised for photosynthesis, but, also protect chlorophyll-a from photo-oxidation., , 3. Direction Read the following passage and answer, the questions that follows., Akshita who is a biology tutor was teaching, photosystems to the students at her place. While, explaining the topic light reaction said that, ‘‘Two, of the three products of light reaction, ATP and, NADPH are used to drive the reactions in the, biosynthetic/dark phase.’’ It has been verified by, , Oxaloacetic Acid (OAA) in C4 -plants are first stable, products of photosynthesis., , (iv) Why is proton gradient is important in, photosynthesis?, Ans. Proton gradient is important as it makes energy available, , for ATP syntheisis., , (v) During dark phase of photosynthesis which is, oxidised and which is reduced?, Ans. NADPH 2 is oxidised and CO2 is reduced in dark phase of, , photosynthesis., , 4. Observe the diagram and answer the following., Atmospheric CO2, Mesophyll cell, , Plasma membrane, Cell wall, – Phosphoenol, HCO3, Pyruvate, , Fixation, , Regeneration, , C4 acid, , C3 acid, , Plasmodesmata, Bundle, sheath cell, , Transport, Transport, Fixation by, C4 acid Calvin cycle, Decarboxylation, , CO2, , C3 acid

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39, , CBSE Term II Biology XI, , (i) Which group of plants exibit these two types of, cells?, Ans. Monocot plants belonging to Graminae/Poaceae family,, , e.g. sugarcane, maize, etc., possess these two types of, cells, i.e. bundle sheath and mesophyll cell (in Kranz, anatomy)., , (ii) What is the first product of C 4 - cycle?, Ans. A 4-carbon compound oxaloacetic acid is the first product, , of C4 - cycle., , (iii) Which enzyme is there in bundle sheath cells and, mesophyll cells?, (NCERT Exemplar), Ans. Mesophyll cells have PEP carboxylase to fix atmospheric, , CO2 to form a 4-carbon compound oxalo acetic acid,, whereas bundle sheath cells have RuBP carboxylase, which fix CO2 by this enzyme to form 3-carbon, compound 3 PGA (3 phosphoglyceric acid)., , 5. The following figure shows the effect of light on the, , Rate of photosynthesis, , rate of photosynthesis. Based on the graph, answer, the following questions., , E, , B, , C, , (i) At which point in the curve, light acts as a limiting, factor?, Ans. Light is the limiting factor in region A. In the given, , graph, rate of photosynthesis initially increases with an, increase in light intensity (region A)., , (ii) What are characteristics of light which affect the, rate of photosynthesis?, Ans. The light provides energy for photosynthesis. Thus, it is, , one of the major factors, which affects the rate of, photosynthesis. Three characteristics of light, i.e. the, intensity, quality and duration generally influences the, rate., , (iii) At which condition linear relationship between, incident light and rate of CO 2 -fixation is observed?, Ans. At low light intensities, the linear relationship between, , incident light and rate of CO2-fixation occurs., , (iv) What is the effect of green light in plants?, Ans. The green wavelength of light as low energy levels and is, , not useful for photosynthesis. So, if plants get exposure of, green light for long, they may not carry out, photosynthesis that might lead plant cell to starvation and, death., , (v) Identify the incorrect statement., Ans. If low light conditions prevail, both C3 and C4 -plants fail, , A, , to respond to high CO2 conditions, while at high light, intensities both show increase in the photosynthetic rates, but upto a certain limits., D, Light intensity

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Chapter Test, Multiple Choice Questions, , 1. The structures that are formed by stacking of organised, flattened membranous sacs in the chloroplasts are, , Reason (R) Both PS-I and PS-II contain chlorophyll-a., , 2. Assertion (A) Calvin pathway of sugar synthesis is, , 2. Absorption spectrum of chlorophyll-a and the action, spectrum of photosynthesis is identical because, chlorophyll-a, absorbs the maximum light, absorbs the minimum light, absorbs the red and blue light, is found most abundantly, , rate of photosynthesis., Reason (R) Lack of water causes wilting of leaves,, which reduces their surface area., , (a) it is 700 times more efficient than other pigment molecules, (b) its absorption and action spectra show peaks at 700 nm, (c) it is rendered ineffective at wave length above 700 nm, (d) it is a unit consisting of 700 chlorophyll molecules, , I. Cyclic photophosphorylation needs PS-I and PS-II., II. Cyclic photophosphorylation produces NADPH + H +, and ATP., III. Cyclic photophosphorylation involves H2O., IV. Electrons are recycled in cyclic photophosphorylation., , Identify the correct and incorrect statements and select, the option accordingly., (a), (b), (c), (d), , I, II and III are incorrect, IV is correct, I, II and IV are incorrect, III is correct, I, III and IV are incorrect, II is correct, II, III and IV are incorrect, I is correct, , 5. Consider the following statements., I. H2S not H2O is involved in photosynthesis of sulphur, bacteria., II. ATP is produced during light reaction via chemiosmosis., III. Absence of light leads to the stoppage of, photosynthesis., , Choose the correct option., (b) I, III and IV, (d) I, II and III, , Assertion-Reasoning MCQs, , Answers, Multiple Choice Questions, 1. (a), , 2. (c), , 3. (b), , 4. (a), , 1. (b), , 2. (a), , 3. (a), , 1. Photosynthetic organisms occur at different depths, in the ocean. Do they receive the light? How do they, adapt to carry out photosynthesis under these, conditions?, (NCERT Exemplar), 2. Two groups (A and B) or bean plants of similar size, and same leaf area were placed in identical, conditions. Group A was exposed to light of, wavelength 400-450 nm and Group B to the light of, wavelength of 500-550 nm. Compare the, photosynthetic rate of the two groups by giving, reason., , 3. 3CO 2 + 9 ATP + 6 NADPH + Water →, , Glyceraldehyde, 3-phosphate + 9 ADP + 6 NADP +, 6 Pi., Analyse the above reaction and answer the, following questions., (i) How many molecules of ATP and NADPH are, required to fix one molecule of CO 2 ?, (ii) Where in the chloroplast does this process occur?, , 4. Name the two important enzymes of C3 and C 4, , 5. How does water stress affect/decrease the rate of, photosynthesis?, , Long Answer Type Questions, , Direction (Q. Nos. 1-3) Each of these questions contains, two statements, Assertion (A) and Reason (R). Each of these, questions also has four alternative choices, any one of, which is the correct answer. You have to select one of the, codes (a), (b), (c) and (d) given below., , Assertion-Reasoning MCQs, , Short Answer Type Questions, , pathways, respectively? What important role do they, play in fixing CO 2 ?, , IV. Calvin cycle occurs in grana., (a) II, III and IV, (c) I, II and IV, , same in C3 and C 4 -plants., Reason (R) C3 is the only pathway for synthesis of, sugar from CO 2 ., , 3. Assertion (A) Lack of water indirectly decreases the, , 3. P700 is named because, , 4., , 1. Assertion (A) The absorption spectrum of, chlorophyll-a shows close correlation with its action, spectrum., , (a) grana, (b) stroma lamellae, (c) stroma, (d) cristae, , (a), (b), (c), (d), , (a) Both A and R are true and R is the correct explanation, of A, (b) Both A and R are true, but R is not the correct, explanation of A, (c) A is true, but R is false, (d) A is false, but R is true, , 5. (d), , 1. Six turns of Calvin cycle are required to generate, one mole of glucose. Explain., , 2. Under what conditions are C 4 -plants superior, to C3 ?, , For Detailed Solutions, Scan the code

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41, , CBSE Term II Biology XI, , CHAPTER 03, , Respiration in, Plants, In this Chapter..., , l, , l, , l, , l, , l, , Exchange of Gases in Plants, , l, , Types of Respiration, , l, , Cellular Respiration, , l, , Fermentation, , l, , Aerobic Respiration, , Cellular respiration It is the mechanism of breakdown of, food materials within the cell to release energy and, trapping of this energy for synthesis of ATP., The process by which breaking of the C— C bonds of, complex compounds through oxidation within the cells,, leading to release of considerable amount of energy is, called respiration., The compounds that are oxidised during the process of, respiration are called respiratory substrates. Usually, carbohydrates are oxidised to release energy, but, proteins, fats and even organic acids can be used as, respiratory substrates in some plants, under certain, conditions., During the process of oxidation of food within a cell, all, the energy contained in the respiratory substrates is not, released free into the cell or in a single step. Instead, it, gets released in a series of slow stepwise reactions, controlled by enzymes and it is trapped as chemical, energy in the form of ATP, which is considered as the, energy currency of the cell., , Exchange of Gases in Plants, For the process of respiration, plants take O 2 and release, CO 2 ., The plants have stomata and lenticels for gaseous exchange, instead of specialised organs., , l, , Electron Transport System (ETS), , l, , Oxidative Phosphorylation, , l, , The Respiratory Balance Sheet, , l, , Amphibolic Pathway, , l, , Respiratory Quotient (RQ), , There are several reasons why plants can get along without, respiratory organs., First, each plant part takes care of its own gaseous exchange, needs. There is very little transport of gases from one plant, part to another., Second, plants do not have great demands for gas exchange., Roots, stems and leaves respire at rates far lower than animal, do., Third, the distance that gases must diffuse even in large,, bulky plant is not great. Each living cell in a plant is located, quite close to the surface of the plant., l, , l, , l, , Types of Respiration, We know that during the process of respiration, utilisation of, O 2 takes place with the release of CO2 , water and energy as, products., Cellular respiration may be classified into two types, as given below, , 1. Aerobic Respiration, This is the type of respiration in which organism utilise oxygen, for the complete oxidation of organic food into CO2 , water and, energy. It starts in cytoplasm and get completed inside the, mitochondria., Note Aerobic respiration yields more energy as the respiratory substrate, is completely oxidised in the presence of O 2 .

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42, 2. Anaerobic Respiration, This is the type of respiration in which organic food is, oxidised incompletely. It occurs in cytoplasm and releases, small amount of energy., It is believed that the first cells on this planet lived in an, reducing environment when O 2 was not present in the, atmosphere, i.e., they were anaerobes. Even among present, day living organisms, several are adapted to anaerobic, conditions., Some of them are facultative anaerobes (organisms that have, capability of switching from aerobic to anaerobic conditions, according to the availability of oxygen) while others are, obligate anaerobes (organisms that are killed by normal, atmospheric concentration of oxygen of 21%)., Thus, in any case, all living organisms retain the enzymatic, machinery for partial oxidation of glucose in the absence of, oxygen. And this breakdown of glucose to pyruvic acid is, called glycolysis. It occurs in cytoplasm of the living cell., , Cellular Respiration, It occurs in all living cells and proceeds with the help of, enzymes. The first step in respiration (taking glucose as, substrate) is called glycolysis (glucose is oxidised to pyruvic, acid). After which the pyruvic acid may enter the Krebs’, cycle (aerobic respiration) or undergo fermentation, (anaerobic respiration)., , Glycolysis, l, , l, , l, , l, , Glycolysis (Gr. Glycos–sugar; lysis–splitting), is a stepwise, process by which one molecule of glucose (6C) breaks, down into two molecules of pyruvic acid (3C)., The scheme of glycolysis was given by Gustav Embden,, Otto Meyerhof and J Parnas and is often referred as the, EMP pathway. It is a common pathway in both aerobic and, anaerobic modes of respiration. But in case of anaerobic, organisms, it is the only process of respiration., Glycolysis occurs in the cytoplasm of the cell. During the, process, glucose gets partially oxidised. In plants, this, glucose is derived from sucrose (end product of, photosynthesis) or from storage carbohydrates., During the course of this process in plants, sucrose is first, converted into glucose and fructose by the action of, invertase enzyme, after this, these two monosaccharides, enter the glycolytic pathway., , Steps Involved in Glycolysis, In glycolysis, a chain of 10 reactions, often reactions occur, under the control of different enzymes., It involves the following steps, Step I Phosphorylation of glucose occurs under the action, of an enzyme hexokinase and Mg 2+ that gives rise, to glucose-6-phosphate by the utilisation of ATP., , CBSE Term II Biology XI, , Step II Isomerisation of this phosphorylated, glucose-6-phosphate takes place to form, fructose-6-phosphate with the help of an enzyme, phosphohexose isomerase (reversible reaction)., Step III This fructose-6-phosphate is again phosphorylated, by ATP in order to form fructose 1, 6-bisphosphate, in the presence of an enzyme phosphofructokinase, and Mg 2+ ., The steps of phosphorylation of glucose to fructose, 1, 6-bisphosphate (i.e. from step 1 to 3) activates the, sugar thus, preventing it from getting out of the cell., Step IV Splitting of fructose 1, 6-bisphosphate takes place, into two triose phosphate molecules,, i.e. dihydroxyacetone-3-phosphate and, 3-phosphoglyceraldehyde (i.e. PGAL). This reaction, is catalysed by an enzyme aldolase., ATP, ADP, , Glucose, (6C), I, , Glucose-6-phosphate, (6C), II, , Fructose-6-phosphate, (6C), ATP, III, ADP, Fructose 1, 6-bisphosphate, (6C), IV, Triose phosphate, (dihydroxyacetone, phosphate), (3C), , Triose phosphate, (glyceraldehyde-3-phosphate) (3C), +, NAD, NADH+H, , 2 Triose bisphosphate, (1, 3-bisphosphoglycerate) (3C), ADP, ATP, , VI, , 2 Triose phosphate, (3-phosphoglycerate) (3C), VII, , 2-phosphoglycerate, ATP, H2O, , VIII, , 2-phosphoenol pyruvate, ADP, ATP, , IX, , 2 Pyruvic acid, (3C), , Steps of glycolysis, , V

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43, , CBSE Term II Biology XI, , Step V Each molecule of PGAL removes two redox, equivalents in the form of hydrogen atom and, transfer them to a molecule of NAD + (this NAD +, forms NADH + H + ) and accepts inorganic, phosphate (Pi) from phosphoric acid. This reaction in, turn leads to the conversion to PGAL (which gets, oxidised) to 1, 3-bisphosphoglycerate (reversible, reaction)., Step VI 1, 3-bisphosphoglycerate is converted to, 3-phosphoglycerate with the formation of ATP., This reaction is catalysed by an enzyme, phosphoglycerate kinase. It is also known as energy, yielding process. The formation of ATP directly from, metabolites constitutes substrate level, phosphorylation (reversible reaction)., Step VII In this step, 3-phosphoglycerate is subsequently, isomerised to form 2-phosphoglycerate, catalysed by, enzyme phosphoglyceromutase (reversible reaction)., 2+, , Step VIII In the presence of enzyme enolase and Mg , with the, loss of a water molecule, 2-phosphoglycerate is, converted to Phosphoenol Pyruvate or PEP (reversible, reaction)., Step IX High energy phosphate group of Phosphoenol Pyruvate, (PEP) is transferred to a molecule of ADP, by the action, of enzyme pyruvate kinase in the presence of Mg 2+ and, K + . This in turn produces two molecules of pyruvic, acid (pyruvate) and a molecule of ATP by substrate, level phosphorylation. The pyruvic acid thus,, produced is the key product of glycolysis., Metabolic Fate of Glycolysis, The overall reaction of glycolysis can be depicted as, Glucose + 2Pi + 2ADP + 2NAD + → 2 Pyruvate + 2ATP +, 2NADH + 2H +, Two molecules of NADH on oxidation produce 6 molecules, of ATP. Therefore, a net gain of 8 ATP molecules occurs, during glycolysis., The fate of glycolysis depends upon the availability of oxygen, in the cell. In the presence of oxygen, pyruvic acid will enter, the mitochondrion and undergo complete oxidation of glucose, to CO 2 and H 2 O in aerobic respiration (Krebs' cycle and, ETC)., On the other hand in the absence of oxygen, the pyruvic acid, will undergo anaerobic respiration (lactic acid fermentation, or alcoholic fermentation)., , l, , l, , l, , l, , l, , Kostytcher (1902) coined the term anaerobic respiration., , l, , Glycolysis has two phases, i.e. preparatory (glucose is broken down, to glyceraldehyde-3-phosphate) and pay-off phase (the GAL-3-PD4, is changed into pyruvate producing NADH and ATP)., , Fermentation, Various microorganisms, bacteria, animals and plants are, known to catabolise pyruvic acid into various organic, compounds depending upon the specific enzymes they, possess., Some of these types are as follows, (i) During alcoholic fermentation, in fungi (e.g. yeast), and some higher plants, the incomplete oxidation of, glucose is achieved under anaerobic condition by a, series of reactions in which pyruvic acid is converted to, CO 2 and ethanol., It is done under two steps, (a) Pyruvic acid is first decarboxylated to acetaldehyde, formed in the presence of enzyme pyruvic acid, decarboxylase., CH 3 CCOOH → CH 3 CHO + CO 2, (Acetaldehyde), , (b) This acetaldehyde is further reduced to ethyl, alcohol or ethanol in the presence of enzyme, i.e., alcohol dehydrogenase., CH 3 CHO + NADH + H+ → C 2H 5 OH, (Ethanol), +, , + NAD, (ii) During lactic acid fermentation occuring in muscles,, organisms like some bacteria produce lactic acid as an, end product from pyruvic acid., During the reduction, the pyruvic acid produced in, glycolysis is reduced by NADH 2 to form lactic acid,, CO 2 is not produced and NADH 2 is oxidised to, NAD + . This reaction is catalysed by a lactic acid, dehydrogenase, FMN proteins and Zn 2+ ions., Glucose, , Glyceraldehyde, 3-phosphate, NAD+, , Lactic, acid, NAD+, , NADH+H+, NADH+H+, 3-Phosphoglyceric, Pyruvic, acid, acid, NADH+H+, NAD+, Phosphoenol, pyruvic acid, , Ethanol+CO2, , Major pathways of anaerobic respiration, , Likewise, in case of animal cells also (such as muscles), during exercise, when there is inadequate amount of, oxygen for cellular respiration, pyruvic acid is reduced to, lactic acid in the presence of enzyme lactate, dehydrogenase., Thus in both the processes, oxidation of reducing, (NADH + H + ) agent takes place.

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44, , CBSE Term II Biology XI, , Energy Yield in Fermentation, In both alcoholic and lactic acid fermentation, the energy, released is very less, i.e. not more than 7% of the energy is, released from glucose and not all of it is trapped as high, energy bonds of ATP., Also, the fermentation processes are proved to be hazardous, in nature because either acid or alcohol is produced on, oxidation. Apart from this, yeasts may also poison themselves, to death if the concentration of alcohol reaches about 13%., , Aerobic Respiration, It is the next step (after glycolysis) that leads to complete, oxidation of organic substances. It occurs in the presence of, oxygen. The oxygen acts as a final acceptor of electron and, protons are removed from the substrate. The final product of, glycolysis, i.e. pyruvic acid is transported into from the, cytoplasm mitochondria and thus, the second phase of, respiration is initiated., The process of aerobic respiration involves two crucial events, (i) The complete oxidation of pyruvate occurs by the, stepwise removal of all the hydrogen atoms, thereby,, leaving three molecules of CO 2 . This occurs in the, matrix of mitochondria., (ii) The electrons removed as part of the hydrogen atoms, are then passed on to molecular O 2 with the, simultaneous synthesis of ATP. This on the contrary, takes place on the inner membrane of the mitochondria., , Oxidative Decarboxylation of Pyruvic, Acid, In mitochondria, pyruvic acid (formed by the glycolytic, catabolism of carbohydrates in cytosol) undergoes oxidative, decarboxylation (i.e. removal of CO 2 in aerobic conditions), forming a key compound, i.e. acetyl Co-A by the action of, pyruvic acid dehydrogenase (in mitochondrial matrix), through a series of reactions., Pyruvic acid + Co-A + NAD, , +, , participate in the reaction catalysed by pyruvic acid, dehydrogenase. It was first elucidated by Sir Hans Krebs, a, British Biochemist in 1940. The whole cycle explains how, pyruvate is broken down to CO 2 and water., Following are the steps of Krebs’ cycle, (i) Condensation The Krebs' cycle starts with the, condensation of acetyl group with oxaloacetic acid and, water to yield citric acid, a 6C compound. This is the, first stable product of the cycle. This step is catalysed by, an enzyme, citrate synthetase. Co-A is liberated during, this reaction., (ii) Citric acid then undergoes reorganisation in two steps, in order to form in the presence of an enzyme cis, acotinase intermediate., (iii) Oxidative Decarboxylation Isocitrate is followed by two, successive steps of oxidative decarboxylation that leads, to the formation of α-ketoglutaric acid, (a 5C compound, in the presence of an enzyme, isocitrate dehydrogenase, and Mn 2+ ) and then succinyl Co-A, catalysed by, α-complex., The succinyl Co-A then splits into a 4C compound succinic acid, and Co-A with the addition of water. During this conversion, a, molecule of GTP (Guanosine Triphosphate) is synthesised, (catalysed) by an enzyme, succinyl Co-A synthetase (this, occurs when coenzyme-A transfers its high energy to a, phosphate group add to GDP to make GTP molecule)., Note, , (i) GTP is also an energy carrier like ATP. Thus, this is the only, high energy phosphate produced in the Krebs’ cycle., (ii) In plant cells, this reaction also produces ATP from ADP., , In the remaining steps of Krebs’ cycle, succinyl Co-A is, oxidised to oxaloacetic acid, a 4C compound following the, formation of fumaric acid and malic acid catalysed by enzymes,, succinate dehydrogenase and fumarase, respectively., Pyruvate, (3C), Co-A, NAD+, NADH+H+, CO2, Acetyl coenzyme-A, (2C), , Mg2 +, , →, , Pyruvate dehydrogenase, , Acetyl Co-A + CO 2 + NADH + H +, Thus, acetyl Co-A acts as a connecting link between, glycolysis and citric acid cycle., During this process, two molecules of NADH are produced, by breaking down of two molecules of pyruvic acid (produced, from one glucose molecule during glycolysis)., , Tricarboxylic Acid (TCA) Cycle, The acetyl Co-A then enters a cyclic pathway, Krebs’ cycle, (Tricarboxylic Acid Cycle or TCA) in mitochondrial matrix., Various coenzymes including NAD + and Co-A also, , Oxaloacetic acid, (4C), , NAHD+H, , +, , Citric acid, (6C) CO, , 2, , +, , NAD, , Malic acid, (4C), FADH2, FAD+, , NAD+, , NADH+H+, α-ketoglutaric acid, (5C), CO2, NAD+, NADH+H+, Succinic acid, GDP+Pi, (4C), GTP, , The citric acid cycle or Krebs’ cycle

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45, , CBSE Term II Biology XI, , Output of Krebs’ Cycle or Citric Acid Cycle, l, , l, , l, , During this cycle of reactions, 3 molecules of NAD + are, reduced to NADH + H + and one molecule of FAD + is, reduced to FADH 2 . And also one molecule of ATP is, reduced directly from GTP (by substrate level, phosphorylation)., For continuous oxidation of acetyl Co-A, continued, replenishment of oxaloacetic acid is necessary. In addition, to this, regeneration of NAD + and FAD + from NADH and, FADH 2 , respectively are also required., The summary equation for this phase of respiration is as, follows, Pyruvic acid + 4NAD + FAD + + 2H 2 O + ADP + Pi, Mitochondrial matrix, , → 3CO 2 + 4NADH + 4H +, + FADH 2 + ATP, Till now, glucose has been broken down to release CO 2, and 8 molecules of NADH+H + , 2 FADH 2 are, synthesised and just 2 molecules of ATP., , membrane). Now, via cytochrome-b c 1 complex, (complex-III). Cytochrome-c, acts as a mobile carrier for, transfer of electrons between complexes-III and IV., , l, , (iii) The complex-IV, known as cytochrome-c oxidase, complex contains cytochromes-a, a 3 and two copper, centres., During the course of transfer, when electrons pass from, one carrier molecule to another (via complexes-I to IV) in, the electron transport chain, they get coupled to ATP, synthase (i.e. complex-V) for the production of ATP from, ADP and inorganic phosphate. The number of ATP, molecules synthesised depends on the nature of the, electron donor., Inter-membrane, space, , Inner Mitochondrial, membrane, , NADH + H+, 4H+, (Fe–S), , Importance of Citric Acid Cycle, , I, , UQ, e–, UQH2, , Electron Transport System (ETS), , l, , l, , (ii) Reducing equivalents are also received by ubiquinone, via FADH 2 (complex-II), generated during the, oxidation of succinate in the citric acid cycle., This reduced ubiquinone (ubiquinol) is then oxidised, with the electron transfer to cytochrome-c (small, protein attached to the outer surface of the inner, , NAD, , Complex-I, (NADH dehydrogenase), , e–, , (ii) Many intermediate compounds of this cycle are used in, the synthesis of other biomolecules., , At the end of Krebs’ cycle, the oxidation of glucose is, completed as it has given out 6CO 2 molecules. But the, energy obtained till now is very less (i.e. 2ATPs in each, glycolysis and Krebs’ cycle). Thus, the full amount of, energy is yet to be obtained from substrate, i.e. glucose., This occurs through the following steps in the respiratory, process and utilises the energy stored in the NADH+H +, and FADH 2 ., Electron Transport System (ETS) is the metabolic pathway, through which the electron passes from one carrier to, another. It occurs in the inner mitochondrial membrane., The electron transport system consists of four enzyme, complexes, which are arranged in a series on the inner, membrane of the mitochondria., (i) Electrons from NADH produced in citric acid cycle are, oxidised by NADH dehydrogenase (complex-I) and are, transferred to ubiquinone located within the inner, membrane of the mitochondria., , 2e–, , FMN, , The citric acid cycle is important in the following ways, (i) This is the major pathway for the formation for ATP, molecules., , l, , Matrix, , e–, , III, Cyt-c, , 4H+, , Cyt-b, , Fe–S, , Complex-III, (Cytochrome-bc1), , e–, Cyt-c, , Complex-II, (Succinate, dehydrogenase), , UQH2, UQ, II, , e–, (Fe–S), , Succinate, , FAD, , Fumarate, , Cyt-c, e–, 1 +, 2H, O, 2 2, 2H+, , IV, , Cu, 2H+, Cyt-a, , Cyt-a3, , Cu, , H2 O, Complex-IV, (Cytochrome-c, oxidase), , F0, , ADP+Pi, , F1, , ATP, synthase, , ATP, H+, , +, +, +, +, , Electrochemical, gradient, , –, –, –, –, , Electron Transport System (ETS)

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46, l, , l, , CBSE Term II Biology XI, , One molecule of NADH on oxidation provides 3 molecules of, ATP while one FADH 2 produces 2 molecules of ATP,, because its redox potential is higher than NADH and thus,, enters the ETS after bypassing the first site of, phosphorylation. The electrons are finally accepted by oxygen, having the highest redox potential in the series which along, with H + ions form water., Aerobic process of respiration takes place only in the presence, of O 2 , the role of O 2 is limited at the terminal stage of the, process. Yet, the presence of oxygen is vital because it drives, the whole process by removing hydrogen from the system., , Oxidative Phosphorylation, l, , l, , l, , l, , l, , l, , l, , Net Gain of ATP, Due to all the criteria mentioned above, it is predicted, that there can be net gain of 36 ATP molecules from one, molecule of glucose during aerobic respiration as given, below, , It is the synthesis of energy rich ATP molecules with the help, of energy liberated by oxidation of reduced coenzymes, produced during respiration. Oxidative phosphorylation in, mitochondria is catalysed by a multicomponent enzymatic, complex called ATP synthase, (complex-V) or coupling factor., The ATP synthase complex consists of two major components, (i) F 1 -particle The head piece is a peripheral membrane, protein complex and contains the site for ATP synthesis, from ADP and inorganic phosphate., , Glycolysis, , (ii) F0 -particle It is an integral membrane protein complex, that forms the channel through which protons cross the, inner membrane., The passage of protons through the channel is coupled to the, catalytic site of the F1 component for the production of ATP., For every 2H + that passes through F 0 from the, intermembrane space to the matrix (down the electrochemical, proton gradient), one ATP molecule is produced., , In eukaryotic cells, 2 molecules of ATP are spent for, transporting 2 molecules of NADH formed during, glycolysis (in the cytoplasm) to the mitochondria, hence, the net gain is 36 molecules of ATP., , Pyruvic acid to, acetyl Co-A, , Outer, side, 2H+, , Inner mitochondrial, membrane, , F0, , 2H+, , 2 ATP, , 2 molecules of NADH, , =, , 6 ATP, , 2 molecules of NADH, , =, , 6 ATP, , =, , 18 ATP, , =, , 4 ATP, , 2 molecules of GTP, , =, , 2 ATP, , Total, , =, , 38 ATP, , Amphibolic Pathway, l, , l, , F1, Matrix, ADP Pi, , Diagrammatic representation of ATP synthesis in mitochondria, l, , The Respiratory Balance Sheet, The complete aerobic breakdown of one molecule of glucose, results in the release of 2 molecules of NADH from glycolysis., And 8 molecules of NADH and 2 molecules of FADH 2 within, the mitochondrial matrix., The calculation of the net gain of ATP for every glucose, molecule oxidised can be made only on certain assumptions., All pathways function in an orderly sequential manner with, one substrate forming the next with glycolysis, TCA cycle and, ETS pathway following one after another., , =, , 2 molecules of FADH, , Head, , Stalk, , 2 ATP directly, , Citric acid cycle 6 molecules of NADH, , ATP, , l, , NADH synthesised during glycolysis is transferred into, the mitochondria for oxidative phosphorylation., None of the intermediates in the pathway are utilised to, synthesise any other compound., Only glucose is being respired, no other alternative, substrates are entering in the pathway at any of the, intermediary stages., , l, , The term amphibolic is used to denote a biochemical, pathway involving both catabolism and anabolism,, e.g. the citric acid cycle, acts as a central metabolic, pathway that completes the oxidative degradation of, monosaccharides, fats and amino acids., Usually, glucose is the primary substrate for respiration, for most of the organisms. All carbohydrates are first, converted into glucose before they are used for, respiration. Different substrates like fats and proteins, can also be respired, but they do not enter the, respiratory pathway at the very first step., If fats have to enter the pathway, they first have to be, converted into fatty acids and glycerol. Fatty acids are, then degraded into acetyl Co-A, which enters the citric, acid cycle. Glycerol is first converted to, 3-phosphoglyceraldehyde (PGAL), before entering the, pathway., Likewise, the proteins (if acts as respiratory substrates), are degraded by proteases into individual amino acids, which after deamination (removal of amine group from a, molecule) enters the citric acid cycle either as pyruvate or, acetyl Co-A.

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47, , CBSE Term II Biology XI, , Thus, it is clear from the above discussion that respiration, involves breakdown of organic compounds. It has been, considered as catabolic process and the respiratory pathway is, called catabolic pathway., But at the same time certain intermediates of respiratory, pathway are also withdrawn in order to synthesise other, compounds, e.g. fatty acids would be broken down to acetyl, Co-A, but when organisms need to synthesise fatty acids acetyl, Co-A would be withdrawn from respiratory pathway., Hence, respiratory pathway comes into picture both during, breakdown and synthesis. Breaking down processes within, living organism is catabolism and synthesis is anabolism., Thus, it would be better to consider the respiratory pathway as an, amphibolic pathway rather than as a catabolic one., l, , l, , l, , Fats, Fatty acids and glycerol, , Carbohydrates, , Proteins, , Simple sugars, e.g. glucose, , Amino acids, , Glucose-6-phosphate, Fructose-1,6-bisphosphate, Dihydroxyacetone phosphate, , Glyceraldehyde-3-phosphate, , Respiratory Quotient (RQ), Respiratory quotient is the ratio of the volume of CO 2, evolved to the volume of O 2 consumed in respiration. It, is also known as respiratory ratio., Volume of CO 2 evolved, RQ =, Volume of O 2 consumed, The respiratory quotient tends to vary with respiratory, substrate used during respiration., This can be understood from following, (i) Respiratory Quotient of Carbohydrates When, carbohydrates are used as substrate and are, completely oxidised, the RQ is always 1 (because, amount of CO 2 evolved is always equal to the, amount of O 2 consumed)., C 6H12 O 6 + 6O 2 → 6CO 2 + 6H 2 O + Energy, 6CO 2, RQ =, = 1.0, 6O 2, (ii) Respiratory Quotient of Fats If the respiratory, substrate is fat, then RQ of the respiring cells will, be less than 1, because the volume of CO 2 evolved, is quite less in comparison to the volume of O 2, being consumed., Calculations for a fatty acid, tripalmitin, if used as a, substrate is shown below, 2(C 51 H 98 O 6 ) + 145 O 2 →, Tripalmitin, , 102 CO 2 + 98 H 2 O + Energy, , Pyruvic acid, , RQ =, , Acetyl Co-A, H2O, , Krebs’, cycle, , 102CO 2, = 0.7, 145O 2, , Note Fats always require more amount of O 2 for their, oxidation as compared to the other substrates., CO2, , Interrelationship among metabolic pathway showing respiration mediated, breakdown of different organic molecules to CO2 and H2O, , (iii) Respiratory Quotient of Proteins If the, respiratory substrate is protein then the RQ is, variable, i.e. it varies from 0.5 to 0.9 depending upon, the oxygen content of the substrate.

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48, , CBSE Term II Biology XI, , Chapter, Practice, PART 1, Objective Questions, l, , Multiple Choice Questions, 1. Glycolysis is, , (a) oxidative process, (b) reductive process, (c) physical process, (d) biological process, Ans. (a) Glycolysis is the oxidative process of breakdown of, hexose sugar to release some energy as ATP and reducing, agent as NADH 2., , 2. In glycolysis, NADH + H + is formed from NAD, when, (a) 3-phosphoglyceraldehyde (PGAL) is converted to, 1, 3-bisphosphoglycerate (BPGA), (b) triose phosphate is converted to 2-phosphoglycerate, (c) 2-phosphoglycerate is converted to 2-phosphopyruvate, (d) 2-phosphopyruvate is converted to 2-pyruvic acid, Ans. (a) Out of all the ten reactions taking place in glycolytic, cycle, NADH + H + is formed only during conversion of, PGAL to BPGA., , 3. Select the correct order of reactions in glycolysis., I. Conversion of 3-phosphoglyceraldehyde to, 1, 3-bisphosphoglycerate, II. Conversion of 3-phosphoglyceric acid to, 2-phosphoglycerate, III. Conversion of BPGA to 3-phosphoglyceric acid, IV. Splitting of fructose 1, 6-bisphosphate into, dihydroxyacetone phosphate and, 3-phosphoglyceraldehyde, Codes, (a) IV, III, I, II, (b) II, III, I, IV, (c) II, IV, I, III, (d) IV, I, III, II, Ans. (d) The correct sequence is IV → I → III → II., , 4. In animal cells like muscles, during exercise, when, O 2 is inadequate for cellular respiration, pyruvic, acid is reduced into lactic acid by, (a) O2, (b) carboxylation, (c) lactate dehydrogenase, (d) None of the above, Ans. (c) In animal cells like muscles, during exercise, when O2, is inadequate for cellular respiration, pyruvic acid is, reduced into lactic acid by lactate dehydrogenase., , 5. Pyruvate → Ethyl alcohol + CO 2, The above reaction needs two enzymes which are, (a) pyruvate decarboxylase and alcohol dehydrogenase, (b) pyruvate decarboxylase and enolase, (c) pyruvate decarboxylase and pyruvate kinase, (d) pyruvate carboxylase and aldolase, Ans. (a) In fermentation by yeast, the incomplete oxidation of, glucose is achieved under anaerobic conditions by sets of, reaction, where pyruvic acid is converted to ethanol and, CO2. The enzymes, pyruvic decarboxylase and alcohol, dehydrogenase catalyse these reactions., , 6. In eukaryotes, most of the TCA cycle enzymes are, present in, (a) cytoplasm, (b) intermembrane space of mitochondria, (c) mitochondrial matrix, (d) inner membrane of mitochondria, Ans. (c) In eukaryotes, all the reactions of Tricarboxylic Acid, (TCA) cycle or Krebs’ cycle take place in the matrix of, mitochondria because all enzymes of this cycle are found, in the matrix of mitochondria except succinic, dehydrogenase, which is located in the inner membrane, of mitochondria., In prokaryotes, Krebs’ cycle occurs in cytoplasm.

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49, , CBSE Term II Biology XI, , 7. Which one of following is complex-V of the ETS, of inner mitochondrial membrane?, , molecule during respiration,, , (a) NADH dehydrogenase, (b) Cytochrome oxidase, (c) Ubiquinone, (d) ATP synthase, Ans. (d) The complex-V of the ETS of inner mitochondrial, membrane is ATP synthase. This complex consists of, two major components, F1 (peripheral membrane, protein) and F0 (integral membrane protein)., , 8. Match the following columns about ETS., Column I, (ETS complexes), , 11. Out of 36 ATP molecules produced per glucose, (a) 2 are produced outside glycolysis and 34 during, respiratory chain, (b) 2 are produced outside mitochondria and 34 inside, mitochondria, (c) 2 during glycolysis and 34 during Krebs’ cycle, (d) All are formed inside mitochondria, Ans. (b) Out of 36 ATP molecules, 2 ATP are produced during, glycolysis in cytoplasm of the cell, i.e. outside the, mitochondria. 34 ATP are produced by Krebs’ cycle,, oxidative phosphorylation and ETC, inside mitochondria., , 12. The last or terminal cytochrome in respiratory chain is, , Column II, (Names), , A., , Complex-I, , 1. NADH dehydrogenase, , B., , Complex-II, , 2. Succinate dehydrogenase, , C., , Complex-III, , 3. Cytochrome-bc1 complex, , (a) cytochrome-a, (b) cytochrome-a 3, (c) cytochrome-c, (d) cytochrome-f, Ans. (b) Cytochrome-a 3 is the last or terminal cytochrome in, respiratory chain., , D., , Complex-IV, , 4. Cytochrome-c oxidase complex, , 13. Glycerol is a product of fat breakdown. It sometimes, , Codes, A B C D, (a) 1 4 3 2, (c) 2 3 1 4, Ans. (b) A–1, B–2, C–3, D–4, , A B C D, (b) 1 2 3 4, (d) 3 4 1 2, , 9. Given below is the diagrammatic presentation of, ATP synthesis in mitochondria. Identify A-C and, choose the correct option accordingly., ATP, , Outer, side, , Stalk, 2H+, , A, B, Inner mitochondrial, membrane, , C, Matrix, ADP Pi, , +, , (a) A− H , B −F1, C−F0, (b) A−3H + , B −F0, C−F1, (c) A−2H +, B −F0 , C−F1, (d) A−5H +, B −F1, C−F0, Ans. (c) A−2H +, B −F0 , C−F1, , 10. Calculation of ATP gain for every glucose is made, on certain assumptions. Choose the correct option, in accordance with the statement given below., (a) The pathway functioning is sequential and orderly, (b) One substrate forms the reactant for the others, (c) TCA cycle and ETS pathway follow one after, another, (d) All of the above, Ans. (d) All the given statements are correct in accordance, with ATP gain., , enters the respiratory pathway after being converted to, (a) Fatty acids, (b) PEP, (c) PGAL, (d) None of these, Ans. (c) Glycerol would enter the respiratory pathway after, being converted to PGAL., , 14. The Respiratory Quotient (RQ) or respiratory ratio is, Volume of O2 evolved, Volume of CO2 consumed, Volume of O2 consumed, (b) RQ =, Volume of CO2 evolved, Volume of CO2 consumed, (c) RQ =, Volume of O2 evolved, Volume of CO2 evolved, (d) RQ =, Volume of O2 consumed, (a) RQ =, , Ans. (d) The ratio of the volume of CO2 evolved to the volume of, , O2 consumed in respiration is called the Respiratory, Quotient (RQ) or respiratory ratio., Volume of CO2 evolved, RQ =, Volume of O2 consumed, , 15. Select the incorrect statement., (a) When tripalmitin is used as a substrate in respiration,, the RQ is 0.7, (b) The intermediate compound, which links glycolysis with, Krebs’ cycle is malic acid, (c) One glucose molecule yields a net gain of 36 ATP, molecules during aerobic respiration, (d) One glucose molecule yields a net gain of 2 ATP, molecules during fermentation, Ans. (b) Statement in option (b) is incorrect and can be corrected, as, The intermediate compound between the glycolysis and, Krebs’ cycle is acetyl Co-A., Rest of the statements are correct.

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50, l, , CBSE Term II Biology XI, , Assertion-Reasoning MCQs, , Ans. (d) A is false, but R is true because, , Complex-II of ETS is succinate dehydrogenase, complex., Cytochrome-c is a small protein attached to the outer, surface of the inner mitochondrial membrane and acts, as a mobile carrier for the transfer of electrons between, complexes-III and IV of ETS., , Direction (Q. Nos. 1-5) Each of these questions, contains two statements, Assertion (A) and Reason, (R). Each of these questions also has four alternative, choices, any one of which is the correct answer. You, have to select one of the codes (a), (b), (c) and (d), given below., (a) Both A and R are true and R is the correct explanation, of A, (b) Both A and R are true, but R is not the correct, explanation of A, (c) A is true, but R is false, (d) A is false, but R is true, , 5. Assertion (A) Respiratory pathway is considered, as an amphibolic pathway., Reason (R) It involves both anabolism and, catabolism., Ans. (a) Both A and R are true and R is the correct, , explanation of A., Respiratory pathway is considered as an amphibolic, pathway as it involves both anabolic and catabolic, reactions. For example, fatty acids are broken down to, acetyl Co-A before entering respiratory pathway and, many other carbonic acids are synthesised as an, intermediate compound., , 1. Assertion (A) Glycolysis occurs in cytoplasm., Reason (R) Enzymes for glycolysis are found in, cytoplasm. It is common in aerobic/anaerobic, respiration., Ans. (a) Both A and R are true and R is the correct explanation, , of A., , 2. Assertion (A) The conversion of glyceraldehyde, -3- phosphate into 1,3- bisphosphoglycerate is an, oxidation reaction., Reason (R) The reaction in which 1, 3-bisphosphoglycerate is formed from glyceraldehyde3-phosphate utilises NAD + ., Ans. (a) Both A and R are true and R is the correct explanation, , of A., The conversion of glyceraldehyde-3-phosphate to, 1, 3-bisphosphoglycerate is an oxidation reaction., This oxidation reaction occurs due to the use of NAD+, which gets converted to NADH by accepting a hydrogen, molecule and this reaction is catalysed by the enzyme, glyceraldehyde-3-phosphate dehydrogenase., , 3. Assertion (A) In glycolysis, 4 ATPs are produced., Reason (R) The net gain of ATP in glycolysis is, 8 ATP., Ans. (b) Both A and R are true, but R is not the correct, , explanation of A., , 4. Assertion (A) NADH dehydrogenase is the, complex-II of ETS., Reason (R) Cytochrome-c acts as a mobile carrier for, the transfer of electrons between complexes-III and, IV of ETS., , l, , Case Based MCQ, 1. Direction Read the following passage and answer, the questions that follows., Electron transport system is a metabolic pathway, through which electrons pass from one carrier to, another. It is a part of aerobic respiration in which, electrons removed from intermediate compounds, in glucose catabolism are accepted by the final, electron acceptor at the end of ETC. It consists of, four large multiprotein complexes and two small, diffusible electron carriers. The electrons passing, through ETC gradually lose energy. The end, products of ETC are water and ATP., (i) The main purpose of electron transport chain is to, , (a) release and utilise energy stored in NADH + H+ and, FADH 2, (b) use the intermediate from TCA cycle, (c) breakdown pyruvic acid, (d) All of the above, Ans. (a) The main purpose of ETC (Electron Transport, Chain) is to release and utilise the energy stored in, NADH + H+ and FADH2. This is accomplished when, these are oxidised through the electron transport system, and the electrons are passed on to O2, resulting in the, formation of H 2O.

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51, , CBSE Term II Biology XI, , (ii) In the electron transport system present in the, inner mitochondrial membrane, complexes-I and IV, are, respectively, (a) NADH dehydrogenase and FADH 2, (b) NADH 2 and NADH dehydrogenase, (c) NADH dehydrogenase and cytochrome oxidase, complex, (d) NADH dehydrogenase and ATP synthetase, Ans. (c) In ETS, complex-I is NADH dehydrogenase and, complex-IV is cytochrome oxidase complex., , (iii) How many cytochromes are involved in the, electron transport chain?, (a) Five, , (b) Two, , (c) Six, , (d) Four, , Ans. (a) In electron transport system, five cytochromes are, , involved namely, cytochromes (cyt-b, c, c1 , a, a 3)., , (iv) The fourth complex of ETC has, (a) cytochrome-b only, (b) cytochrome-a only, (c) cytochromes-a, c and a 3, (d) cytochromes-a and b, Ans. (c) Complex-IV refers to cytochrome-c oxidase complex, containing cytochromes-a and a 3 and two copper centres., , (v) In mitochondria, protons accumulate in the, (a) outer membrane, (b) inner membrane, (c) intermembrane space, (d) matrix, Ans. (c) In respiration, protons accumulate in the, intermembrane space of the mitochondria when electrons, move through the ETS., , PART 2, Subjective Questions, l, , Short Answer (SA) Types Questions, , glucose that is utilised. This shows that aerobic, respiration produces much more energy than anaerobic, respiration, which produces only 2 ATP molecules., So, aerobic respiration is more efficient., , 1. If a person is feeling dizzy, glucose or fruit juice is, given immediately, but not a cheese sandwich,, which might have more energy. Explain., (NCERT Exemplar), , 5. ‘Respiration is an energy releasing and, enzymatically controlled catabolic process, which, involves a stepwise oxidative breakdown of organic, substances inside living cells’. In this statement, about respiration explain the meaning of, (i) stepwise oxidative breakdown, (ii) organic, substances (used as substrates). (NCERT Exemplar), , Ans. If a person is feeling dizzy, glucose or fruit juice is given, , immediately because it is readily oxidised and oxidation, of 1 g of glucose yields more energy than a cheese, sandwich., , 2. What are respiratory substrates? Name the most, common respiratory substrate., , (NCERT), , Ans. The organic substances, which are catabolised in the, , living cells to release energy are called as respiratory, substrates. Though any food stuff-carbohydrate, fat or, protein may act as a respiratory substrate, the common, respiratory substrate is glucose., , 3. Comment on the statement, ‘respiration is an, energy producing process, but ATP is being used in, some steps of the process’., Ans. Respiration is a complex oxidative process in which, , formation of several intermediate molecules occurs. In, the end, water molecule is produced and ATP molecules, are released in cell. Although ATP molecules are also, used in the some steps of glycolysis and Krebs’ cycle,, there is also production of more molecules of ATP, thus a, positive balance of ATP molecules is obtained., , 4. What is meant by the statement ‘aerobic respiration, is more efficient’?, , (NCERT Exemplar), , Ans. The aerobic respiration is a high energy yielding process., , During the process of aerobic respiration as many as, 36, molecules of ATP are produced for every molecule of, , Ans., , (i) Stepwise Oxidative Breakdown Respiration is a, stepwise oxidation of organic molecules in a cell, involving main three steps, (a) Glycolysis, (b) Krebs’ cycle, (c) Electron transport, chain, Glucose passes through series of enzymatically, controlled reactions and is finally converted into, H 2O + ATP + CO2, (ii) Organic Substances (used as substrates) The organic, substances, which are catabolised in the living cells, to release energy are called as respiratory substrates., Though any food stuff-carbohydrate, fat or protein, may act as a respiratory substrate, the common, respiratory substrate is glucose because it can be, oxidised easily and is present abundantly., , 6. What is the significance of stepwise release of, energy in respiration?, , (NCERT), , Ans. During oxidation within a cell, all the energy contained in, , respiratory substrates is not released freely in a single, step. It is released in a series of slow stepwise reactions

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52, , CBSE Term II Biology XI, , controlled by enzymes and it is trapped as chemical, energy in the form of ATP. The significance of this, stepwise release of energy is that some energy is used to, synthesise ATP which is stored for the later utilisation, wherever, required. Hence, ATP acts as the energy, currency of cell., The energy stored in ATP can be utilised following, (i) In various energy requiring processes of organisms., (ii) The carbon skeleton produced during respiration is, used as precursors for the synthesis of other, molecules., , 12. Name the end products of aerobic and anaerobic, fate of glycolysis. List two ways by which molecules, of ATP are produced in glycolysis during aerobic, respiration in a cell., Ans. End product of aerobic glycolysis, O2, , Pyruvic acid → CO2 + Water, End products of anaerobic glycolysis are CO2 and ethanol, or lactic acid., Molecules of ATP are produced in two ways in glycolysis by, (i) direct transfer of phosphate to ADP., (ii) oxidation of NADH produced during glycolysis to, NAD + ., , 7. We commonly call ATP as the energy currency of, the cell, why? Can you think of some other energy, carriers present in a cell? Give name any two., Ans. ATP is known as the energy currency of the cell because, , 13. Study the following figure and labelled as A, B, C, and D pathway of anaerobic respiration in yeast., , it acts as reservoir of energy and it releases energy. The, other energy carriers present in a cell are ADP and AMP., , Glucose, , 8. What are the main steps in aerobic respiration?, (NCERT), Ans. The main steps in aerobic respiration are as follows, , (i) Glycolytic breakdown of glucose into pyruvic acid., (ii) Oxidative decarboxylation of pyruvic acid to acetyl, Co-A., (iii) Krebs’ cycle, (iv) Terminal oxidation and phosphorylation in, respiratory chain., , Glyceraldehyde, 3-phosphate, A, B, 1, 3-bisphosphoglyceric, acid, NAD+ C, +, NADH+H+, D, , 9. ATP produced during glycolysis is a result of, substrate level phosphorylation. Explain., (NCERT Exemplar), , Phoshoenol, pyruvic acid, , Ans. Substrate level phosphorylation is a type of metabolism, , that results in the formation and creation of Adenosine, Triphosphate (ATP) or Guanosine Triphosphate (GTP) by, the direct transfer and donation of a phosphoryl (PO 3), group to Adenosine Diphosphate (ADP) or Guanosine, Diphosphate (GDP) to form a phosphorylated reactive, intermediate., , Ans. A – NAD + , B – NADH + H + , C – Ethyl alcohol,, , D – CO 2, Fermentation involves conversion of NAD + to, NADH + H + (A and B) when glyceraldehyde-3-phosphate, changes to 1, 3-bisphosphoglyceric acid., Pyruvic acid, in the absence of oxygen forms ethyl alcohol, and CO2 (C and D)., , 10. Write the reaction where substrate level, phosphorylation takes place in glycolysis., Ans. Substrate level phosphorylation takes place during the, , following reactions, (i) When 1, 3-bisphosphoglycerate is converted into, 3-phosphoglycerate., (ii) When phosphoenol pyruvate is converted into, pyruvic acid., , 11. Write two energy yielding reactions of glycolysis., Ans. The conversion of BPGA to 3-phosphoglyceric acid, , (PGA), is an energy yielding process, this energy is, trapped by the formation of an ATP. Another ATP is, synthesised during the conversion of PEP to pyruvic acid., , Pyruvic, acid, , 14. (i) What is the end product of glycolysis and where, does this process occur?, (ii) List the conditions under which fermentation, occurs in plant cells., Ans., , (i) End product of glycolysis, Glucose + 2ADP + 2Pi + 2NAD → 2 Pyruvic acid, + 2ATP + 2NADH 2, It occurs in cytoplasm, i.e. outside the mitochondria., (ii) Fermentation in plant cells occurs in the absence of, oxygen.

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53, , CBSE Term II Biology XI, , 15. What is fermentation? Name any two organic, compounds produced in the process., Ans. Anaerobic respiration is also called fermentation. It, , involves the production of energy from food nutrients in, the absence of oxygen., Organic compounds produced in the process are, (i) Ethyl alcohol in yeast cell, (ii) Lactic acid in muscles., , 16. List two instances where lactic acid is formed by, fermentation., Ans. Instances where lactic acid is formed by fermentation are, , (i) During fermentation, by lactic acid bacteria., (ii) During strenuous exercise, in the striated muscles in, humans., , 17. Anaerobic respiration cannot continue for long in, , 19. Differentiate between anaerobic respiration and, fermentation., Ans. Differences between anaerobic respiration and, , fermentation are as follows, Anaerobic Respiration, , Fermentation, , It occurs inside the cell., , It occurs outside the, organism., , It occurs only in the absence of It occurs independent of, O2 and can be changed to, O2 and cannot be changed, aerobic respiration when O2 is to aerobic respiration., present., It occurs in microorganisms,, higher plant and animal cells., , It occurs in, microorganisms only., , This process occurs through, several enzymes., , It is a single step reaction, which occurs by an, enzyme complex., , higher organisms.Why?, Ans. Anaerobic respiration cannot continue for long in higher, , organisms because of, (i) low yield of energy, (ii) decomposition of large amount of substrates, so that, little is left for growth and repairs, (iii) toxic effect of end products in higher concentration, (iv) inhibition of a number of physiological process, linked with aerobic respiration., , 18. Differentiate between aerobic and anaerobic, respiration., Ans. Differences between aerobic and anaerobic respiraton, , are as follows, Aerobic Respiration, , Anaerobic Respiration, , It is common in all higher, plants., , It is uncommon in higher, plants., , It is a permanent process, and goes on throughout the, life of plants., , It occurs for a temporary, phase under anaerobic, conditions in higher plants., , Energy released in larger, amount in the form of ATP, (36 ATP)., , Energy released in lesser, amount in the form of 2 moles, of ATP., , It occurs in the presence of, O2 ., , It occurs in the absence of O2 ., , End products are CO2 and, H 2 O., , End products are ethanol and, CO2 ., , 20. Differentiate between lactic acid fermentation and, alcoholic fermentation., Ans. Differences between lactic acid and alcoholic, , fermentation are as follows, Lactic Acid Fermentation, , Alcoholic Fermentation, , During this, the pyruvate, During this, the pyruvate, molecules are broken down, molecules are broken down, into lactic acid molecule only. into ethyl alcohol molecule, and carbon dioxide, molecule., It takes place in human, muscles., , It takes place by yeast and, some bacterial forms., , Industrially this process is, used to make yogurt and, cheese., , Industrially this process is, used to make bread, bear, and vinegar., , 21. What is the metabolic fates of pyruvic acid?, Ans. The three metabolic products formed under aerobic and, , anaerobic conditions from pyruvic acid are, (i) Lactic acid is formed by the oxidation of pyruvic, acid in under anaerobic condition in skeletal, muscles., (ii) Ethanol is formed by the oxidation of pyruvic acid in, yeast under anaerobic condition., (iii) Acetyl Co-A is formed by the oxidation of pyruvic, acid that take place within the mitochondria under, aerobic condition.

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54, , CBSE Term II Biology XI, , 22. When does anaerobic respiration occur in man and, , 26. Do you know any step in the TCA cycle, where, , yeast?, , there is substrate level phosphorylation? Which, one?, (NCERT Exemplar), , Ans. Anaerobic respiration occurs in man in muscles at the, , time of excessive exercising. Blood supply does not meet, the oxygen demand of the exercising body. At that time in, muscle, lactic acid is produced as a result of anaerobic, respiration. In yeast, also anaerobic respiration occurs in, the condition of absence of oxygen., , Ans. In TCA cycle, during the conversion of succinyl Co-A to, , succinic acid, a molecule of GTP is synthesised. This is a, substrate level phosphorylation. In a coupled reaction,, GTP is converted to GDP with the simultaneous, synthesis of ATP from ADP., , 23. Complete the following equation of conversion of, , 27. Where is cytochrome-c located? What is its function?, , pyruvic acid into acetyl coenzyme-A. Where does, this process occur inside the cell?, , Ans. Cytochrome-c is attached to the outer surface of the inner, , membrane of mitochondria., Function It acts as a mobile carrier for transfer of, electrons between complex-III and complex-IV., , Mg 2+, , Pyruvic acid + Co-A + … →, Pyruvate dehydrogenase, , 28. (i) Where is the respiratory electron transport system, , Acetyl Co-A + … + …, Ans. Pyruvic acid + Co-A + NAD, , located in a cell?, (ii) What compound is the terminal electron acceptor, in aerobic respiration?, , Mg 2+, , +, , →, , Pyruvate dehydrogenase, , Acetyl Co-A + CO 2 + NADH, The pyruvic acid, produced in the cytosol by the process, of EMP pathway, enters into mitochondria where it is, converted into acetyl Co-A inside the matrix., , 24. Name the site (s) of pyruvate synthesis. Also, write, the chemical reaction, wherein pyruvic acid, dehydrogenase acts as a catalyst., , 29. Oxygen is critical for aerobic respiration. Explain, its role with respect to ETS., , process of glycolysis., The chemical reaction, wherein pyruvic acid, dehydrogenase acts as a catalyst is as follows, The reactions catalysed by pyruvic dehydrogenase, require the participation of several coenzymes, including, NAD + and Co-A., Mg 2+, Pyruvic acid + Co-A + NAD + →, Pyurvate dehydrogenase, Acetyl Co-A + NADH + H+, , 25. Does pyruvic acid enter the Krebs’ cycle directly?, Ans. No, before pyruvic acid as such does not enter Krebs’, , cycle, pyruvate is first decarboxylated and then oxidised, by the enzyme pyruvate dehydrogenase to form acetyl, Co-A. This molecule enters the mitochondria for further, oxidation reaction. This is the connecting link between, glycolysis and Krebs’ cycle., +, , During the process, NAD is reduced to NADH + H ., The summary of the reaction is given below, Pyruvic acid + Co-A + NAD +, , (i) The respiratory electron transport system is located, in the inner membrane of mitochondria., (ii) Oxygen is the terminal electron acceptor in aerobic, respiration., , Ans. Oxygen is critical for aerobic respiration due to following, , Ans. Pyruvate synthesis takes place in cytoplasm by the, , +, , Ans., , Pyruvate dehydrogenase, , →, Mg 2+, , Acetyl Co-A + CO2 + NADH + H +, During this process, two molecules of NADH are, produced (from the metabolism of two molecules of, pyruvic acid produced during glycolysis) and thus, it, results in a net gain of 6 ATP molecules (2 NADH × 3 = 6, ATP)., , reasons, (i) It acts as the terminal acceptor of hydrogen., (ii) It drives the whole process by removing hydrogen, from the system., , 30. Differentiate between oxidative phosphorylation, and electron transport chain., Ans. Differences between oxidative phosphorylation and, , electron transport chain are as follows, Oxidative, Phosphorylation, , Electron Transport Chain, , It utilises products of the, Krebs’ cycle., , It is driven by the process of, proton pumping by complexes-I,, III and IV., , It generates ATP from, energy stored by the, electron transport chain., , It consumes NADPH and, FADH 2 ., , ATP is not needed for O2, consumption., , Here, O2 serves as an electron, acceptor, so the ETC drives O2, consumption., , ATP synthase activation, does not alter the, chemiosmotic gradient., , ATP synthase activation increases, the rate at which energy is, removed from the gradient., , 31. Discuss the respiratory pathway is an amphibolic, pathway., Ans. The term amphibolic is used to denote a biochemical, , pathway involving both catabolism and anabolism,, e.g. the citric acid cycle, acts as a central metabolic

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55, , CBSE Term II Biology XI, , pathway that completes the oxidative degradation of, monosaccharides, fats and amino acids., Respiration involves breakdown of organic compounds., It has been considered as catabolic process and the, respiratory pathway is called catabolic pathway., But at the same time certain intermediates of respiratory, pathway are also withdrawn in order to synthesise other, compounds, e.g. fatty acids would be broken down to, acetyl Co-A, but when organisms need to synthesise, fatty acids acetyl Co-A would be withdrawn from, respiratory pathway., Hence, respiratory pathway comes into picture both, during breakdown and synthesis. Breaking down, processes within living organism is catabolism and, synthesis is anabolism. Thus, it would be better to, consider the respiratory pathway as an amphibolic, pathway rather than as a catabolic one., , 32. Define respiratory quotient. What is its value for, fats., , (NCERT), , Ans. Respiratory quotient is the ratio of the volume of CO 2, , evolved to the volume of O 2 consumed in respiration., It is also known as respiratory ratio., Volume of CO2 evolved, RQ =, Volume of O2 consumed, The respiratory quotient tends to vary with respiratory, substrate used during respiration., Respiratory Quotient of Fats If the respiratory, substrate is fat, then RQ of the respiring cells will be less, than 1, because the volume of CO 2 evolved is quite less, in comparison to the volume of O 2 being consumed., Calculations for a fatty acid, tripalmitin, if used as a, substrate is shown below, 2(C51H 98O6 ) + 145 O2 →, Tripalmitin, , 102 CO2 + 98 H 2O + Energy, RQ =, , 102CO2, = 0.7, 145O2, , 33. What would be the RQ value of yeast if it were to, respire glucose anaerobically?, Ans. The RQ will be infinity (∞) during anaerobic respiration., , In anaerobic respiration, CO 2 is evolved, but oxygen is, not used. Therefore, RQ in such a case, will be infinite., e.g. C6H12O6 → 2C2H 5OH + 2CO2 + Energy, RQ =, , 2CO2 (2 molecules), = Infinity, O2(zero molecules), , 34. When is RQ slightly more than unity?, Ans. RQ slightly more than unity is found when organic acids, , are broken down as respiratory substrates under aerobic, conditions, e.g., 2(COOH)2 + O2 → 4CO2 + 2H 2O, Oxalic acid, , RQ, , 4CO2, = 4.0, 1O2, , C4H 6O5 + 3O2 → 4CO2 + 3H 2O, Malic acid, , RQ =, l, , 4CO2, = 1. 3, 3O2, , Long Answer (LA) Type Questions, 1. Define the following, (i) Respiration, (ii) Respiratory substrate, (iii) How does a tree trunk exchange gases with the, environment although it lacks stomata?, (iv) Which is the most important energy carrier? Is this, compound mobile?, (v) Name the major respiratory substrates used by, most organisms. If unavailable at time, what other, substances can be used for respiration?, , Ans., , (i) Enzyme controlled process of biological oxidation of, various organic food materials in a living cell,, producing CO2 and H 2O and releasing energy in the, form of ATP is called respiration., (ii) The organic compounds catabolised in the living cells, to release energy are called respiratory substrates., (iii) Gaseous exchange without stomata can take place due, to the presence of lenticels in the periderm which is, connected internally to the network of parenchyma, with outside world., (iv) The most important energy carrier is ATP. This energy, rich compound is mobile, but cannot pass from one cell, to another., (v) Carbohydrates are major respiratory substrates. In, condition of its unavailability, proteins, fats and, organic acids can be used., , 2. Give an account on glycolysis., Ans. Glycolysis is a stepwise process by which one molecule of, , glucose (6C) breaks down into two molecules of pyruvic, acid (3C).

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56, , CBSE Term II Biology XI, , It involves the following steps, Step I Phosphorylation of glucose occurs under the action, of an enzyme hexokinase and Mg 2+ that gives rise to, glucose-6-phosphate by the utilisation of ATP., Step II Isomerisation of this phosphorylated, glucose-6-phosphate takes place to form, fructose-6-phosphate with the help of an enzyme, phosphohexose isomerase (reversible reaction)., Step III This fructose-6-phosphate is again phosphorylated, by ATP in order to form fructose 1, 6-bisphosphate in the, presence of an enzyme phosphofructokinase and Mg 2+ ., Step IV Splitting of fructose 1, 6-bisphosphate takes place, into two triose phosphate molecules, i.e. dihydroxyacetone, 3-phosphate and 3-phosphoglyceraldehyde (i.e. PGAL)., This reaction is catalysed by an enzyme aldolase., ATP, ADP, , Glucose, (6C), , Step V In this step, dihydroxyacetone phosphate is, isomerised into glyceraldehyde-3-phosphate in the, presence of enzyme triose phosphate isomerase., Step VI Each molecule of PGAL removes two redox, equivalents in the form of hydrogen atom and transfer, them to a molecule of NAD+and accepts inorganic, phosphate (Pi) from phosphoric acid. This reaction in, turn leads to the conversion to PGAL (which gets, oxidised) to 1, 3-bisphosphoglycerate (BPGA), i.e., reversible reaction., Step VII 1, 3-bisphosphoglycerate is converted to, 3-phosphoglycerate with the formation of ATP., This reaction is catalysed by an enzyme, phosphoglycerate kinase., Step VIII In this step, 3-phosphoglycerate is, subsequently isomerised to form 2-phosphoglycerate,, catalysed by enzyme phosphoglyceromutase., Step IX In the presence of enzyme enolase and Mg 2+ with, the loss of a water molecule, 2-phosphoglycerate is, converted to Phosphoenol Pyruvate (PEP)., Step X High energy phosphate group of Phosphoenol, Pyruvate (PEP) is transferred to a molecule of ADP, by the, action of enzyme pyruvate kinase in the presence of Mg 2+, and K + . This in turn produces two molecules of pyruvic, acid (pyruvate) and a molecule of ATP by substrate level, phosphorylation. The pyruvic acid thus, produced is the, key product of glycolysis., , Mg2+, I, , Glucose-6-phosphate, (6C), Mg2+, II, Fructose-6-phosphate, (6C), ATP, III, ADP, Fructose 1, 6-bisphosphate, (6C), , 3. Explain the major steps of Krebs’ cycle. Where, does this process occur in a cell?, , IV, , Ans. Krebs’ cycle (Tricarboxylic Acid Cycle or TCA) occurs in, Triose phosphate, (glyceraldehyde-3-phosphate) (3C), V, +, NAD, VI, NADH+H, 2 Triose bisphosphate, (1, 3-bisphosphoglyceric acid) (3C), ADP, ATP, , VII, , 2 Triose phosphate, (3-phosphoglyceric acid) (3C), VIII, , 2-Phosphoglycerate, ATP, Mg2+, H2O, IX, 2 Phosphoenol pyruvate, ADP, ATP, , Mg2+, X, , 2 Pyruvic acid, (3C), , Steps of glycolysis, , Triose phosphate, (dihydroxyacetone, phosphate), (3C), , the mitochondrial matrix., Following are the steps of Krebs’ cycle, (i) The Krebs' cycle starts with the condensation of, acetyl group with oxaloacetic acid and water to, yield citric acid, a 6C compound. This is the first, stable product of the cycle., This step is catalysed by an enzyme citrate, synthetase. Co-A is liberated during this reaction., (ii) Citrate is isomerised to isocitrate., (iii) Isocitrate is followed by two successive steps of, oxidative decarboxylation that leads to the, formation of α-ketoglutaric acid (a 5C compound in, the presence of an enzyme isocitrate, dehydrogenase and Mn 2+ ) and then succinyl Co-A,, catalysed by α-complex., The succinyl Co-A then splits into a 4C compound, succinic acid and Co-A with the addition of water., During this conversion, a molecule of GTP, (Guanosine Triphosphate) is synthesised (catalysed), by an enzyme succinyl Co-A synthetase (this occurs, when coenzyme-A transfers its high energy to a, phosphate group add to GDP to make GTP, molecule).

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57, , CBSE Term II Biology XI, , In the remaining steps of Krebs’ cycle, succinyl, Co-A is oxidised to oxaloacetic acid, a 4C, compound following the formation of fumaric acid, and malic acid catalysed by enzymes succinate, dehydrogenase and fumarase, respectively., , 5. Write down the differences between glycolysis and, Krebs’ cycle., Ans. Differences between glycolysis and Krebs'cycle are as, , follows, , Pyruvate, (3C), Co-A, NAD+, NADH+H+, CO2, Acetyl coenzyme-A, (2C), , Oxaloacetic acid, (4C), , NAHD+H, , +, , Citric acid, (6C) CO, , 2, , NAD+, Malic acid, (4C), FADH2, FAD+, , NAD+, , NADH+H+, α-ketoglutaric acid, (5C), CO2, NAD+, Succinic acid, NADH+H+, GDP+Pi, (4C), GTP, , Citric acid cycle or Krebs’ cycle, , 4. Describe output of TCA cycle in terms of its end, products. Also, discuss its importance in the, metabolism of living cell., Ans. Output of Krebs’ Cycle or Citric Acid Cycle, , During this cycle of reactions, 3 molecules of NAD +, are reduced to NADH + H + and one molecule of, FAD + is reduced to FADH 2. And also one molecule of, ATP is reduced directly from GTP (by substrate level, phosphorylation). For continuous oxidation of acetyl, Co-A, continued replenishment of oxaloacetic acid is, necessary. In addition to this, regeneration of NAD +, and FAD + from NADH and FADH 2, respectively are, also required., The summary equation for this phase of respiration is, as follows, Pyruvic acid + 4NAD + FAD + + 2H 2O + ADP + Pi, Mitochondrial matrix, , → 3CO 2 + 4NADH + 4H +, + FADH 2 + ATP, Till now, glucose has been broken down to release CO2, and 8 molecules of NADH + H + , 2 FADH 2 are, synthesised and just 2 molecules of ATP., Importance of Citric Acid Cycle, The citric acid cycle is important in the following ways, (i) This is the major pathway for the formation for, ATP molecules., (ii) Many intermediate compounds of this cycle are, used in the synthesis of other biomolecules., , l, , Glycolysis, , Krebs’ Cycle, , It takes place in the, cytoplasm., , It takes place in the matrix of, mitochondria., , It is a linear pathway., , It is a cyclic pathway., , It occurs in aerobic as well, as anaerobic respiration., , It occurs in aerobic respiration, only., , It consumes 2 ATP, molecules., , It does not consume ATP., , It yields 2 NADH per, glucose molecule., , It yields 6 NADH molecules, and 2 FADH 2 molecules from, 2 acetyl coenzyme-A, molecules., , It generates 2 ATP, molecules net from, 1 glucose molecule., , It generates 2 GTP/ATP, molecules from 2 acetyl, coenzyme-A molecules., , It oxidises glucose partly,, producing pyruvate., , It completely oxidises acetyl, coenzyme-A., , It does not produce CO 2 ., , It produces CO 2 ., , All enzymes catalysing, glycolytic reactions are, dissolved in cytosol., , Two enzymes of Krebs’ cycle, reactions are located in the, inner mitochondrial, membrane, all others are, dissolved in matrix., , Case Based Questions, 1. Direction Read the following passage and answer the, questions that follows., There are three major ways in which different cells, handle pyruvate (pyruvic acid) produced by, glycolysis. These are lactic acid fermentation,, alcoholic fermentation and aerobic respiration., Fermentation takes place under anaerobic conditions, in many prokaryotes and unicellular eukaryotes. For, the complete oxidation of glucose to CO 2 and H 2 O,, however, organisms adopt Krebs’ cycle which is also, called as aerobic respiration. This required O 2 supply., In fermentation, the incomplete oxidation of glucose, is achieved under anaerobic conditions by sets of, reactions where pyruvate is converted to CO 2 and, ethanol. Other organisms like bacteria produce lactic, acid from pyruvic acid. In animal cells also, like, muscles during exercise, when oxygen is inadequate, for cellular respiration, pyruvic acid is reduced to, lactic acid.

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58, , CBSE Term II Biology XI, , In both lactic acid and alcohol fermentation, not, much energy is released., (i) In which processes, CO 2 is not released?, Ans. In lactate fermentation, CO2 is not released. Lactic, , acid fermentation is a process by which glucose, fructose, and sucrose are converted into energy and lactic acid., The reaction for lactic acid fermentation is, 2 NAD+, , 2 (NADH +H +), Lactate, dehydrogenase, , 2 Pyruvic acid, FMN, Zn, , 2 Lactic acid, , 2+, , (ii) Which compound acts as reducing agent in lactic, acid and alcoholic fermantation?, Ans. NADH+ H + acts as reducing agent in alcoholic and lactic, , acid fermentation. It is reoxidised to NAD + in both the, processes., , (iii) Which products are formed by pyruvic acid under, aerobic condition?, Ans. Pyruvic acid, the product obtained through glycolysis,, , under aerobic condition forms acetyl Co-A and CO2. It, can be represented as, Mg 2 +, , +, , Pyruvic acid + Co-A +NAD, , →, , Pyruvate dehydrogenase, , Acetyl Co-A +CO2 + NADH + H +, , (iv) How many ATP molecules are produced when a, molecule of glucose undergoes fermentation?, Ans. During fermentation, the pyruvic acid is transformed to, , ethyl alcohol and 4 ATP molecules are produced. This, pyruvic acid comes from breakdown of glucose by, glycolysis., , (v) At which concentration of alcohol, it is poisonous to, yeast?, Ans. Yeast poison themselves to death when the concentration, , of alcohol reaches about 13%., , 2. The flow chart given below depicts the major, pathway of anaerobic respiration. Based on the, figure answer the following questions., Glucose, C, A, NAD+, NADH+H+, 3-phosphoglyceric, acid, B, , NAD+, NADH+H+, NADH+H+, NAD+, , Phosphoenol, pyruvic acid, , Ethanol+CO2, , (i) Identify the A, B and C in the given figure., Ans. Glucose is eventually converted to, , glyceraldehyde-3-phosphate (A) with formation of, intermediates like fructose-6-phosphate and, glucose-6-phosphate., Glyceraldehyde-3-phosphate then forms, 3-phosphoglyceric acid which converts to, 2-phosphoglyceric acid and finally forms pyruvic acid (B), which in the absence of oxygen, forms lactic acid (C)., , (ii) In the production of ethanol, pyruvic acid is first, converted to acetaldehyde by which enzyme?, Ans. In the production of ethanol, pyruvic acid is first, , converted to acetaldehyde by enzyme pyruvate, decarboxylase. The reaction is given below, Pyruvate decarboxylase, , 2CH3COCOOH →, Pyruvic acid, , TPP, Mg 2 +, , 2CH3CHO + 2CO2, Acetaldehyde, , (iii) In yeast during anaerobic respiration, how many, glucose molecules are required for the production, of 38 ATP molecules?, Ans. During anaerobic respiration of yeast, two ATP produced, , from a single glucose molecule. Hence, 38 ATP will be, produced from 19 glucose molecules. Anaerobic, respiration occurs in the absence of oxygen. It is found in, deep-seated tissues of plants and animals, germinating, seeds, yeasts and bacteria., , (iv) Which products are produces by bacteria in, anaerobic respiration?, Ans. In anaerobic respiration, some bacteria produce lactic, , acid from pyruvic acid., , 3. Direction Read the following passage and answer, the questions that follows., The process of respiration in plants includes the, utilisation of carbohydrates produced during, photosynthesis to produce energy which in turn, contributes to the growth of plants. Respiration in, plants occurs in two phases, i.e. light reactions and, dark reactions. The first step of respiration is, glycolysis in which glucose is oxidised to pyruvic, acid. After this, the product of pyruvic acid enters, the Krebs’ cycle which provides the reducing, power to generate many more ATP molecules in the, next stage of aerobic respiration, i.e. the electron, transport chain., (i) Glucose-6-phosphate , → Fructose-6-phosphate, Which enzyme is used in the above reaction?, Ans. Glucose-6-phosphate isomerises to form, , fructose-6-phosphate in the presence of enzyme, phosphohexose isomerase.

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59, , CBSE Term II Biology XI, , (ii) How many molecules of pyruvic acid are formed, in glycolysis?, Ans. During glycolysis, one molecule of glucose (6C) yields, , two molecules of pyruvic acid (3C)., , (iii) What is the name of the 4C compound formed in, Krebs’ cycle?, Ans. Oxaloacetic acid is 4C compound that combines with, , acetyl Co-A (2C) to form citric acid (6C) in Krebs’ cycle., , (iv) Which is the final electron acceptor in the, electron transport system?, Ans. The final electron acceptor in electron transport system, , is oxygen. It has the highest redox potential and, combines with H + ions to form water., , (v) In which part of mitochondria does ATP synthesis, occur?, Ans. The F1 head piece of ATP synthase complex contains the, , site for ATP synthesis., , (iv) Name any two enzymes involved in Krebs’ cycle., Ans. Citrate synthase and isocitrate dehydrogenase are involved, , in Krebs’ cycle at different steps., , (v) Mention any one importance of Krebs’ cycle., Ans. One importance of Krebs’ cycle is that the intermediate, , compounds formed during this cycle are used in the, synthesis of other biomolecules., , 5. The term amphibolic is used to denote a biochemical, pathway involving both catabolism and anabolism., B, , C, , Simple sugars, e.g. glucose, , Amino acids, , A, Fatty acids, and glycerol, , Glucose-6-phosphate, Fructose-1,6-bisphosphate, , 4. Observe the diagram of Krebs’ cycle given below, and answer the questions that follows., , Dihydroxyacetone, phosphate, , Glyceraldehyde-3-phosphate, , Pyruvate, Acetyl coenzyme-A, Oxaloacetic acid, , Pyruvic acid, Acetyl Co-A, , Citric acid, , H2O, , Malic acid, , α-ketoglutaric acid, , Succinic, acid, , (i) Where does Krebs’ cycle take place?, Ans. Krebs’ cycle occurs in mitochondrial matrix as enzymes, , required for Krebs’ cycle are present in the, mitochondrial matrix in close proximity to the electron, transport chain., , (ii) How many CO 2 molecules are released during, one Krebs’ cycle?, Ans. During one Krebs’ cycle, two carbon atoms of acetyl, , Co-A are released which form a CO2 molecule, thus, releasing two CO2 molecules., , (iii) Give one point of difference between glycolysis, and Krebs’ cycle., Ans. The difference between glycolysis and Krebs’ cycle is, , that glycolysis occurs in the cytoplasm whereas Krebs’, cycle occurs in the mitochondrial matrix., , Krebs’, cycle, , CO2, , Answer the following questions., (i) Identify A, B and C., Ans. A–Fats, B–Carbohydrates and C–Proteins., , (ii) State the importance of Krebs’ cycle in the, amphibolic pathway., Ans. Many intermediate compounds of this cycle are used in the, , synthesis of other biologically important molecules., Besides this, it is the major pathway for formation of ATP, molecules required for energy by organisms., , (iii) Pyruvic acid the key product of glycolysis has many, metabolic fates. What does it form under aerobic, conditions?, Ans. Pyruvic acid form CO2 and H 2O with the release of energy, , under aerobic condition., , (iv) Before entering respiratory pathways, fatty acid and, glycerols are converted into ...I... and ...II... ,, respectively., Ans. I–Acetyl Co-A, II–PGAL

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Chapter Test, Multiple Choice Questions, , 2. Assertion (A) TCA cycle begins with the, , 1. Glycolysis is also known as, (a) EMP pathway, (c) CMT pathway, , (b) PME pathway, (d) TMC pathway, , 2. In which of the following conversions, ATP synthesis occurs, during glycolysis?, (a) Glucose → Glucose-6-phosphate, (b) Fructose-6- phosphate → Fructose-1,6-bisphosphate, (c) 1,3-bisphosphoglyceric acid (BPGA) →, 3-phosphoglyceric acid (PGA), (d) All of the above, , 3. What is the correct order of the sequence of aerobic, Krebs’ cycle → Electron transport chain → Glycolysis, Electron transport chain → Krebs’ cycle → Glycolysis, Glycolysis → Krebs’ cycle → Electron transport chain, Glycolysis → Electron transport chain → Krebs’ cycle, , 4. In anaerobic respiration in yeast,, (a), (b), (c), (d), , H2O and CO2 are the end products, CO2 , ethanol and energy are the end products, CO2 and H2O are the end products, CO2 , acetic acid and energy are the end products, , 5. Phase common in aerobic and anaerobic respiration is, (a) Krebs’ cycle, (c) glycogenolysis, , (b) glycolysis, (d) ETS, , Assertion-Reasoning MCQs, Direction (Q. Nos. 1-3) Each of these questions contains, two statements, Assertion (A) and Reason (R). Each of, these questions also has four alternative choices, any one, of which is the correct answer. You have to select one of, the codes (a), (b), (c) and (d) given below., (a), (b), (c), (d), , Reason (R) Last step of TCA cycle is catalysed by, enzyme citrate synthase., , 3. Assertion (A) During strenuous exercise, anaerobic, respiration sometimes occurs in our skeletal, muscles., Reason (R) Pyruvic acid is converted to lactic acid, in the presence of lactate dehydrogenase and in, the absence of oxygen., , Short Answer Type Questions, , cellular respiration?, (a), (b), (c), (d), , condensation of acetyl Co-A with oxaloacetic acid, and water., , Both A and R are true and R is the correct explanation of A, Both A and R are true, but R is not the correct explanation of A, A is true, but R is false, A is false, but R is true, , 1. Assertion (A) Aerobic respiration is bioenergetically more, efficient than anaerobic glycolysis., Reason (R) Aerobic respiration occurs in the presence of, oxygen, while fermentation occurs in the absence of, oxygen., , 1. Energy is released during the oxidation of, compounds in respiration. How is this energy, stored and released as and when it is needed?, , 2. Fill in given blanks., Glucose ....A..... 3-phosphoglyceric acid ....B..., pyruvic acid ...C… + CO 2., , 3. Differentiate between glycolysis and fermentation?, 4. What are the assumptions made during the, , organism. Cells are participating in this process., During this process, ATP, CO 2 and water are, formed. It is not a light dependent process., (i) Name the process., (ii) It is a catabolic or an anabolic process., (iii) What could be the raw material of this process?, (NCERT Exemplar), , Long Answer Type Questions, , 1. Respiratory pathway is believed to be a catabolic, pathway. However, nature of TCA cycle is, amphibolic. Explain., , 2. It is necessary to calculate and study the, respiratory balance sheet occurring during, respiration. Why?, What are the factors taken into account for this, study?, , Answers, Multiple Choice Questions, 1. (a), , 2. (c), , 3. (c), , 4. (b), , Assertion-Reasoning MCQs, 1. (b), , 2. (c), , 3. (a), , 5. (b), , (NCERT), , calculation of net gain of ATP?, , 5. A process is occurring throughout the day in ‘X’, , For Detailed Solutions, Scan the code

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61, , CBSE Term II Biology XI, , CHAPTER 04, , Plant Growth, and Development, In this Chapter..., l, , Plant Growth Regulators (PGRs), , l, , Discovery of Plant Growth Regulators, , l, , Physiological Effects of Plant Growth Regulators, , l, , Interaction between Growth Regulators, , Plant Growth Regulators (PGRs), It has been suggested from sufficient evidences that the plants, have certain chemical substances, which help to control the, mechanism of growth., Plant growth regulators are variously described as plant, growth substances or plant hormones or phytohormones., These are the small, simple organic molecules of diverse, chemical composition produced naturally in higher plants that, control the growth and other physiological functions. These, are required in a very small amount by the plant., , (iv) Terpenes, e.g. Gibberellic Acid (mainly GA 3 ), (v) Gases, e.g. Ethylene ( C2 H 4 )., On the basis of functions, they perform in a living plant body, in broad terms, PGRs are divided into two groups, , 1. Plant Growth Promoters, PGRs that exhibit growth promoting activities such as cell, division, cell enlargement, tropic growth, pattern formation,, flowering, fruiting, seed formation, etc., are called plant, growth promoters, e.g. auxins, gibberellins and cytokinins., , Classification of Plant Growth Regulators, , 2. Plant Growth Inhibitors, , The plant growth regulators fall under the following, categories of chemical groups, (i) Indole Compounds, e.g. Indole-3- Acetic Acid (IAA), (ii) Adenine Derivatives, e.g. N 6 -furfuryl amino purine,, kinetin, (iii) Carotenoid Derivatives, e.g. Abscisic Acid (ABA), , These primarily function in response to wounds and stresses, of biotic and abiotic origin. These are also involved in various, growth inhibiting processes like dormancy and abscission,, e.g. abscisic acid., Note The gaseous form of PGR (like ethylene), can fit in either, category and may function both as promoter and inhibitor. But, largely, it functions as an inhibitor of growth activities.

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62, , CBSE Term II Biology XI, , Discovery of Plant, Growth Regulators, It is interesting to know that the discovery of all five major, groups of plant growth regulators have been done, accidentally. All these help in understanding the, phenomenon of development and abnormal behaviour in, plants., , 1. Discovery of Auxin, l, , l, , l, , This is the first growth hormone to be discovered. The, knowledge of this hormone came into existence through, the observation of Charles Darwin and his son Francis, Darwin., They observed that the coleoptiles of canary grass, responded to unilateral source of light (phenomenon, known as photoperiodism) by growing towards it., After performing series of experiments, they came to the, conclusion that coleoptile tip was the site that has the, property of transmittable influence due to which bending, of complete coleoptile was caused. The first PGR, i.e. auxin, was isolated by FW Went in 1928, from the coleoptile tip, of oat seedlings., , l, , callus (i.e. a mass of undifferentiated cells) proliferated,, only when the nutrient medium containing auxin was, supplemented with the extract of vascular tissues or yeast, or coconut milk (water of endosperm of coconut)., It was later found that the active substance present in, coconut milk is a modified form of adenine which was, crystallised and identified as kinetin. Further the, compounds that exhibited kinetin like properties were, termed as cytokinins., , 4. Discovery of Abscisic Acid, With the progression in the research on plant growth, regulators, three independent researchers reported the, purification and chemical characterisation of three different, kinds of inhibitors (during mid 1960), i.e. inhibitor B,, abscission II and dormin. Later, these were proved to be, chemically identical in nature and were named as Abscisic, Acid (ABA)., , 5. Discovery of Ethylene, Cousins (1910), confirmed the release of a volatile substance, from ripened oranges that enhance the ripening of stored, unripened bananas. This volatile substance was later, identified to be a gaseous plant growth regulator,, i.e. ethylene., , Physiological Effects of Plant, Growth Regulators, (a), , (b), , (c), , (d), , Experiment used to demonstrate that tip of the coleoptile is, the source of auxin. Arrows indicate direction of light, , All five categories of plant growth regulators discussed above,, have the following physiological effects on the growth of the, plant, , 1. Auxins, l, , 2. Discovery of Gibberellins, l, , l, , l, , In early part of 20th century, the bakanae (foolish, seedlings disease of rice), was reported to be caused by a, fungal pathogen, Gibberella fujikuroi., Symptoms shown by the infected plant were elongated, stems, little or no production of grains and plant became, weak. Thus, it was later identified that the active substance, involved here was gibberellic acid., The Japanese plant pathologist E Kurosawa, reported the, appearance of symptoms of the disease in uninfected rice, seedlings when they were treated with sterile filtrate of, the fungus., , 3. Discovery of Cytokinins, l, , F Skoog and his coworkers, studied the nutritional, requirements of tissue culture. They made nutrient, medium derived from the internodal segments of tobacco, stems. They observed that from that internodal segments, a, , l, , Auxin (Gk. auxein to grow) was initially isolated from the, urine of human, but later on, their presence was also found, in plants and was proved to be the first PGR ever known., The real plant auxin is chemically known as, Indole -3-Acetic Acid (IAA)., The term is also applied to other natural and synthetic, compounds having various growth regulating properties., Production of auxin generally takes place in the region of, growing apices of the stems and roots from where they, migrate to the site of their action., , Note Auxins can move only through cell to cell by diffusion, i.e. they, cannot move through vascular tissues., , Types of Auxins, There are generally two basic categories in which auxins, are divided, i. Natural Auxins, , They occur naturally in plants and fungi, e.g. Indole Acetic, Acid (IAA) and Indole Butyric Acid (IBA).

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63, , CBSE Term II Biology XI, , ii. Synthetic Auxins, , These are prepared from synthetic compounds that cause, several responses to IAA. They can easily move in all, directions inside the plants, e.g. Naphthalene Acetic Acid, (NAA), 2, 4- dichlorophenoxyacetic acid (2, 4-D)., All these types of auxins are extensively been used in, agricultural and horticultural practices., l, , The compounds, which can be converted into auxins, are called, auxin precursors, e.g. IAA is synthesised from tryptophan, amino acid hormone., , l, , The compounds, which inhibit the actions of auxins, are termed, anti-auxins., , Functions of Auxins, Auxins perform several functions, these are as follows, (i) Apical Dominance Presence of auxin in higher, concentration (in higher plants) in shoot apex, promotes, apical dominance. It is seen commonly in many, vascular plants, the presence of apical buds does not, allow the lateral buds to grow. They only start, developing into branches when the apical bud is, removed., , (vii) Metabolism Application of auxin can enhance, metabolism due to mobilisation of nutrients and growth, promoting substances., Applications of Auxins, As stated, use of synthetic auxins is widely accepted, now-a-days in various agricultural and horticultural practices., Following are the applications of auxins, (i) Eradication of Weeds Auxins are used as weedicides, and herbicides. Application of 2, 4-dichlorophenoxyacetic acid (2, 4-D) is widely done in order to kill, dicotyledonous weeds. It does not affect mature,, monocotyledonous plants., (ii) Helps in Cell Division Besides cell elongation, auxin, may also play important role in cell division., (iii) Controls Xylem and Phloem Differentiation Auxin, controls differentiation of xylem and phloem in stems, and roots. There are evidences that low concentration, of auxin induces phloem differentiation while higher, concentration of auxin is responsible for differentiation, of both xylem and phloem tissues., , 2. Gibberellins, l, , l, , l, , (a), (b), Apical dominance in plants, (a) A plant with apical bud, intact, (b) A plant with apical bud removed, , (ii) Initiation of Roots In contrast to stem, higher, concentration of auxin inhibits the elongation of shoots,, but it initiates more lateral branches of roots., (iii) Inhibition of Abscission Natural auxins delay, abscission of young fruits and leaves and also used to, control pre-harvest fruit drop., (iv) Cell Elongation Auxin stimulates the elongation of, cells of shoots., (v) Promotes Flowering Presence of auxin helps in, promoting flowering in some plants, e.g. pineapple,, litchi, etc., (vi) Parthenocarpy Auxins are sprayed on to the, unpollinated pistil and make them develop into, parthenocarpic fruits, which carry a better market, values., , These are another group of plant growth regulators, which, are known to be weakly acidic growth hormones. There are, more than 100 different gibberellins reported from widely, different organisms like fungi and higher plants., All of them are known to be acidic in nature, thus they are, termed as Gibberellic Acids (i.e. GA, GA 1 , GA 2 and so on)., However, GA 3 is the most important gibberellic acid, which was first to be discovered. It is most extensively, studied amongst all gibberellins., , Functions of Gibberellins, Gibberellins show various important physiological effects, (i) Elongation of Internodes It helps in elongation of the, internodes so as to increase the height of the plant., They cause an increase in length of axis and is also used, in increasing length of grapes stalks., (ii) Elongation of Genetically Dwarf Plants It has been, seen that if gibberellins are administered to a dwarf, plant (pea, maize, etc), it may help in overcoming, dwarfism. It also causes fruits to elongate and improve, their shape, e.g. in apples, etc., (iii) Bolting The gibberellins also help in promoting, bolting (internode elongation) just prior to their, reproductive phase or flowering. If gibberellin is, sprayed on rosette plants like beet, cabbage, etc., these, plants will show extensive internodal growth and, profuse leaf development.

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64, , CBSE Term II Biology XI, , (iv) Breaking Dormancy It also helps in overcoming, natural dormancy in buds, tubers, seeds, etc., and, helps them to grow., , Naturally Occurring Cytokinins, l, , Coconut Milk Factor The liquid endosperm of coconut is known as, coconut milk. This contains some factors that show kinetin like, activity that enhance and stimulate the growth in many plant tissues, (in vitro). All these factors are collectively called as ‘coconut milk, factor’. These represent an example of naturally occurring cytokinins., , l, , Zeatin It is also a naturally occurring cytokinin, isolated from maize, grains. It is remarkably known to be more active than any other, cytokinin., , Note Seed Dormancy Seed is said to be in the dormant state when, it remains dry and non-germinating even if all conditions for, germination are available. Thus, by ‘breaking seed dormancy’,, we simply mean, to make the seed to germinate., , (v) Flowering This can also be induced in long day, plants by the action of gibberellins., Applications of Gibberellins, Gibberellins, apart from showing varied physiological, effects, also have numerous applications., These are as follows, (i) Delays Senescence Gibberellins can delay the, ripening of fruits such as citrus fruits, apples, etc., This can also be used for safe and prolonged storage, of the fruits., (ii) Malting Process The process of malting in brewing, industry can be speeded up by the use of GA 3 ., (iii) Sugar Yield As carbohydrate is stored in the form, of sugar in the stems of sugarcane. Thus, if crop of, sugarcane is sprayed with gibberellins. It results in, increased internodal length of the stem. This, enhances the increase in the yield of sugarcane as, much as 20 tonnes per acre., (iv) Early Seed Production Plants like Cycas and Pinus, when sprayed GA 3 at juvenille stage, hastens the, maturity period of them leading to early seed, production., , 3. Cytokinins, l, , l, , These are growth promoters that are basic in nature., They have specific effects on cytokinesis (division of, cytoplasm) and were discovered as kinetin (a modified, form of adenine, a purine)., Lethometal (1964), while searching for a substance, with cytokinin like activity, isolated zeatin from corn, kernels and coconut milk. Now presently, several, naturally occurring cytokinins and some synthetic, compounds having cell division promoting activities, have been identified after the discovery of zeatin., , Functions of Cytokinins, Cytokinins have following remarkable physiological effects, (i) Promotes Cell Division This is one of the most common, and important biological effect of kinetin on plants, i.e. to, induce cell division in the presence of sufficient amount of, auxin (IAA)., (ii) Reduces Apical Dominance They promote the growth of, lateral buds by breaking apical dominance., (iii) Morphogenesis Differentiation or morphogenesis of plant, tissues/organs is seen to be in control, if ratio of cytokinins, and auxins is proportionate., (iv) Resistance They also increase resistance of plants to high, or low temperature and diseases., (v) Delays Senescence These also help in delaying senescence, (ageing) of leaves and other organs by controlling synthesis, of protein and mobilisation of resources or nutrients., Applications of Cytokinins, Applications of cytokinins are as follows, (i) Tissue Culture Cytokinins are essential for tissue culture,, apart from cell division, they are also involved in, morphogenesis., (ii) Shelf Life Administration of cytokinins to harvest fruits, and vegetables keeps them fresh for several days and, increase their shelf life., Note Shelf life of flowers and cut shoots can also be increased by dipping, them in cytokinin solutions., , 4. Ethylene, l, , Region of Synthesis of Cytokinins, Natural cytokinins are known to be synthesised in the, regions where rapid cell division takes place, e.g. root, apex, developing shoot, buds, young fruits, etc., out of, these roots are the major source of synthesis of cytokinins,, from where, they move upward through xylem., , l, , It is a simple gaseous plant growth regulator, which is, synthesised from the amino acid, methionine. In plants,, synthesis of ethylene takes place in almost every part of the, plant, i.e. roots, leaves, flowers, seeds, fruits, etc., Most important effect of ethylene is the promotion of, senescent changes in the plant. Thus, it is synthesised by, tissues in large amounts that undergo senescence and also by, ripening fruits, due to this property, it is also known as fruit, ripening hormone.

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CBSE Term II Biology XI, , 65, , Functions of Ethylene, , excessive temperature, etc), it is known as stress hormone. It, acts antagonistically to gibberellic acid., , Ethylene shows various important physiological effects, (i) In dicot seedlings, ethylene influences the horizontal, growth of seedling, swelling of the axis and formation, of apical hook., (ii) It is highly effective in fruit ripening. It also, increases the rate of respiration. This rise in the, respiration rate is called respiratory climacteric., (iii) It helps in breaking seed and bud dormancy., (iv) Initiation of germination in peanut seeds and, sprouting of potato tubers is also due to the, production of ethylene in plants., (v) In deep water rice plants, ethylene promotes rapid, internode and petiole elongation., (vi) It proves to be helpful in increasing absorption, surface of plants by promoting growth of root and, formation of root hairs., (vii) It also stimulates flowering in fruits like pineapple,, mango and other related plants., Applications of Ethylene, As ethylene helps in regulating these many physiological, processes in plants. It is known to be the most widely used, PGR in agricultural field., Ethephon It is the most widely used compound as a, source of ethylene. This tends to absorb readily in an, aqueous solution and transported within the plant. This, slowly releases ethylene. Functions of ethephon are as, follows, (i) Ethephon is known to control fruit ripening, (in tomatoes and apples)., (ii) It also helps in accelerating abscission in flowers and, fruits (causes thinning of fruits like cotton, cherry,, walnut, etc)., (iii) Helps in promoting formation of female flowers,, thus, enhancing the yield of the fruits, e.g. cucumber., , 5. Abscisic Acid (ABA), l, , l, , It is slightly acidic growth hormone that functions as a, growth inhibitor by counteracting with other mentioned, growth hormones, i.e. auxins, gibberellins and, cytokinins., Thus, like other PGR, abscisic acid also has a wide range, of effects on growth and development of plants., As its production is stimulated under stress, (unfavourable conditions such as drought, water lodging,, , Note This hormone is transported to all parts of the plants through the, process of diffusion by conductive channels., , Functions of Abscisic Acid, Abscisic acid shows various important physiological effects, (i) It has a primary role in regulating abscission and, dormancy of buds and seeds. By inducing dormancy, it, helps the seeds to withstand the desiccation and other, factors related to unfavourable growth., (ii) It acts as a general plant growth inhibitor and also, inhibits metabolism of plants., (iii) It has its role in inhibition of seed germination., (iv) Also plays an important role in seed development and, maturation., (v) Abscisic acid stimulates the closure of stomata., The Mechanism of Stomatal Closing by ABA, ABA binds to receptors of the plasma membrane at the surface of the, guard cells., The receptors in turn activate several interconnecting pathways,, which cause a rise in pH in the cytosol promoting the transfer of Ca 2+, from the vacuole to the cytosol., All this causes stomata to close and opening of stomata occurs when, conditions are just reverse to it., , Interaction between Growth, Regulators, For the regulation of every phase of growth, i.e. for, differentiation and developmental processes in plants two or, more phytohormones are intimately related to each other., These can either act synergistically or antagonistically., Thus, every PGR has one or the other role to play. Likewise,, there are also number of events in the life of a plant where, more than one PGR is also involved to affect that particular, event to take place. For example,, (i) Dormancy of seeds and buds is mostly due to abscisic, acid, while it is broken down by gibberellins., (ii) Auxins and cytokinins act antagonistically in controlling, apical dominance, i.e. auxins cause apical dominance,, while cytokinins help to overcome them., (iii) Senescence is prevented by both auxins and cytokinins,, while its stimulation is done by abscisic acid., (iv) Auxins and cytokinins act synergistically in promoting, cell division.

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66, , CBSE Term II Biology XI, , Chapter, Practice, PART 1, Objective Questions, l, , Multiple Choice Questions, 1. Which one includes growth promoters?, , (a) Auxin, cytokinin, ABA, (b) GA, cytokinin, C2H 4, (c) C2H 2, ABA, (d) Auxin, cytokinin, GA 3, Ans. (d) Auxin, cytokinin and GA 3 are growth promoters., , 2. ‘Bakanae’ (foolish seedling) disease of rice, seedlings, was caused by Gibberella fujikuroi,, which is a, (a) fungi, (b) protozoan, (c) bacteria, (d) virus, Ans. (a) Bakanae disease is caused by a fungus, Gibberella, fujikuroi., , 3. Match the following columns., Column I, A., B., C., D., , Darwin and Darwin, E Kurosawa, Skoog and Miller, Cousin, , Column II, 1., 2., 3., 4., , Kinetin, Gibberellic acid, Auxin, Ethylene, , Codes, A B C D, (a) 1 2 3 4, (b) 3 2 1 4, (c) 4 3 2 1, (d) 3 2 4 1, Ans. (b) A–3, B–2, C–1, D–4, , 4. The first hormone to be isolated from human urine, was, (a) auxin, (b) ABA, (c) ethylene, (d) gibberellic acid, Ans. (a) Auxin was first isolated from human urine. Kogl and, Haagen Smith (1931) isolated three chemicals from, human urine and named them as auxin., , 5. Which of the following effects of auxins on plants is, the basis for their commercial application?, (a) Callus formation, (b) Curvature of stem, (c) Induction of root formation in stem cuttings, (d) Induction of shoot formation, Ans. (c) Auxins stimulate root formation on the stem cuttings,, e.g. IAA, IBA, NAA, etc. This application of auxin is, widely used for plant propagation on a commercial basis., , 6. Parthenocarpy in tomatoes is induced by, (a) cytokinin, (b) auxin, (c) gibberellin, (d) CH 2  CH 2, Ans. (b) Parthenocarpy is induced by auxin in tomato., Applications of auxins (e.g. IAA, IBA) and conjugate, auxins (e.g. IBA, alanine) to unpollinated pistils induce, their development into seedless or parthenocarpic fruit., , 7. To get a carpet-like grass, lawns are mowed, regularly this is done to, (a) remove the shoot apical meristem, (b) remove the axillary buds, (c) accelerate the growth of lateral bud, (d) Both (b) and (c), Ans. (c) Removal of shoot tips results in the growth of, axillary/lateral buds. Thus, to accelerate the growth of the, lateral buds and get carpet-like grass, lawns are mowed, regularly., , 8. Auxin promotes flowering and controls xylem, differentiation., (a) True, (c) Cannot say, Ans. (a), , (b) False, (d) Partially true or false, , 9. Apple’s elongation and improvement of its shape is, brought about by, (a) auxin, (b) ethylene (c) C2H 4, (d) GAs, Ans. (d) Gibberellins (GAs) cause fruit like apple to elongate, and improve its shape. They also delay senescence.

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67, , CBSE Term II Biology XI, , 10. Which of the following statement regarding, , 15. Match the following columns and choose the, , gibberellins is incorrect?, , correct option from the codes given below., , (a), (b), (c), (d), , GA 3 was one of the first gibberellins to be discovered, All GAs are acidic, Spraying GA on conifers causes late seed production, Dwarfness can be controlled by treating the plant, with GA 3, Ans. (c) Statement in option (c) is incorrect and can be, corrected as, Spraying juvenile conifers with GA 3 brings about early, maturity period and thus leads to early seed production., Rest of the statements are correct regarding gibberellins., , 11. Difference between the kinetin and zeatin is that, (a) kinetin is active, zeatin is non-active, (b) zeatin is synthetic, kinetin is natural, (c) zeatin is active, kinetin is non-active, (d) zeatin is natural, kinetin is synthetic, Ans. (d) Kinetin does not occur naturally in plants. Search for, natural substances with cytokinin like activity led to the, isolation of zeatin from corn kernels and coconut milk., Thus, zeatin is natural and kinetin is synthetic., , 12. Which hormone helps in increase the surface area, of roots by promoting root growth and root hair, formation?, (a) Cytokinin, (b) Kinetin, (c) Ethylene, (d) ABA, Ans. (c) Ethylene helps plants to increase their absorption, surface area by promoting root growth and root hair, formation., , 13. Identify the effects of ethylene and choose the, correct option accordingly., I. More female flowers in cucumber., II. Alpha-amylase production in barley grain., III. Acceleration of fruit ripening in tomato., IV. Delayed sprouting in potato tubers., Codes, (a) I and II, (b) I and III, (c) III and IV, (d) II and IV, Ans. (b) Statements I and III are the effects of ethylene., , 14. Which plant growth regulator induces triple, response?, (a) C2H 4, (b) IAA, (c) IBA, (d) ABA, Ans. (a) Ethylene ( C2H 4 ) induces triple response. These triple, responses are, (i) inhibited stem elongation, (ii) increased stem thickening, (iii) horizontal growth habit, , Column I, , Column II, , A., , IAA, , 1., , Gases, , B., , N 6-furfuryl amino, purine, , 2., , Terpenes, , C., , ABA, , 3., , Derivatives of, carotenoids, , D., , GA 3, , 4., , Adenine, derivatives, , E., , C 2H 4, , 5., , Indole compounds, , Codes, A B C D E, (a) 1 2 3 4 5, (b) 5 4 3 2 1, (c) 5 4 1 2 3, (d) 4 5 1 2 3, Ans. (b) A–5, B–4, C–3, D–2, E–1, l, , Assertion-Reasoning MCQs, Direction (Q. Nos. 1-5) Each of these questions contains, two statements, Assertion (A) and Reason (R). Each of, these questions also has four alternative choices, any one, of which is the correct answer. You have to select one of, the codes (a), (b), (c) and (d) given below., (a) Both A and R are true and R is the correct, explanation of A, (b) Both A and R are true, but R is not the correct, explanation of A, (c) A is true, but R is false, (d) A is false, but R is true, , 1. Assertion (A) Hormones are also called growth, regulators., Reason (R) These promote or inhibit plant growth., Ans. (a) Both A and R are true and R is the correct explanation, , of A., , 2. Assertion (A) Plants have hormones called, phytohormones., Reason (R) These increase the rate of reactions,, thus always accelerate growth and other related, changes., Ans. (c) A is true, but R is false because, , In plants, growth regulators or plant hormones known as, phytohormones can promote or inhibit various activities, in plant growth and thus are categorised as plant growth, promoters, e.g. auxin, etc., and plant growth inhibitors,, e.g. ethylene.

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68, , CBSE Term II Biology XI, , 3. Assertion (A) Plant Growth Regulators (PGRs) are, very important for plant growth and development., Reason (R) Auxins do not induce flowering in, gymnosperms., Ans. (b) Both A and R are true, but R is not the correct, , explanation of A., Plant Growth Regulators (PGRs) are small, simple, molecules of diverse chemical composition, which in low, concentration regulate growth, differentiation and, development by promoting or inhibiting the same., One type of plant growth regulators are plant hormones, or phytohormones. Auxins are phytohormones. They do, not induce flowering in gymnosperms., , 4. Assertion (A) Removal of shoot tip increases apical, dominance., Reason (R) Due to the accumulation of auxin in, lateral parts, growth is enhanced., Ans. (d) A is false, but R is true. A can be corrected as, , Removal of shoot tip increases the lateral dominance., Further, accumulation of auxin in lateral parts elongate, cells and increases growth., , 5. Assertion (A) ABA acts as antitranspirant., Reason (R) It promotes senescence of leaf., Ans. (b) Both A and R are true, but R is not the correct, , explanation of A., ABA acts as antitranspirant as it induces partial closure of, stomata during drought. It also promotes leaf senescence., l, , Case Based MCQ, 1. Given below are diagrammatic representation of, different stages of plant life and different, phytohormones synthesised in them at that stage., GAs, ABA, , GAs, A, , B, GAs, Cytokinin, , C, Cytokinin, , Ethylene, ABA, , (i) Identify A and C in the above figure., A, C, (a) Ethylene, IAA, (b) ABA, GAs, (c) GAs, IAA, (d) IAA, Ethylene, Ans. (b) A–Abscisic acid and C–GAs. Abscisic acid (ABA), inhibits seed germination and also plays an important role, in seed development and maturation, while GA 3 induces, flowering., , (ii) Which of the following is not a plant growth, inhibitor?, (a) Dormin, (b) IAA, (c) Ethylene, (d) ABA, Ans. (b) IAA is a plant growth promoter, while dormin, abscisic, acid and ethylene are plant growth inhibitors. IAA (Indole, 3-Acetic Acid) is an auxin. Auxins are synthesised in shoot, apices, leaf primordia and developing seeds from the, amino acid, tryptophan. So, IAA is not a plant growth, inhibitor., , (iii) Fruits can be left on the tree longer, so as to, increase the market period. This is due to the, function of, (a) delayed senescence by auxin, (b) delayed senescence by CH 2  CH 2, (c) delayed senescence by cytokinin, (d) delayed senescence by GA, Ans. (d) Gibberellin delays senescence. Thus, the fruits can be, left on tree longer so as to extend the market period by, exposing them to GA., , (iv) Cytokinins help to produce, (a) new leaves and chloroplast in leaves, (b) lateral shoot, (c) adventitious shoot, (d) All of the above, Ans. (d) Cytokinins help to produce new leaves and chloroplast, in leaves, lateral shoot and adventitious shoot., Thus, option (d) is correct., , (v) Respiratory climacteric is related with, , Seed, , Germinated, seed, development, , Actively, growing, plantlet, , Adult, flowering, , Fruit, ripening, , (a) ABA, (b) ethylene, (c) auxin, (d) GA, Ans. (b) Respiratory climacteric is related with ethylene., Climacteric is the sudden rise in respiration that normally, takes place without external influences., It is the stage of fruit ripening associated with increased, ethylene production and a rise in cellular respiration.

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69, , CBSE Term II Biology XI, , PART 2, Subjective Questions, l, , Short Answer (SA) Type Questions, 1. What are plant growth regulators? Name any four, different chemical nature of them with one example, of each., , Ans. Plant growth regulators are small, simple molecules, , secreted in minute quantities that influence various, physiological functions in plants. They are of diverse, chemical composition., (i) Indole compounds [such as- Indole-3- Acetic Acid, (IAA)], (ii) Adenine derivatives [such as kinetin, N 6-furfuryl, amino purine], (iii) Derivatives of carotenoids [such as Abscisic Acid (ABA)], (iv) Terpenes (such as gibberellic acids), , 2. Write short note on discovery of auxin., Ans., , l, , l, , l, , This is the first growth hormone to be discovered. The, knowledge of this hormone came into existence through, the observation of Charles Darwin and his son Francis, Darwin., They observed that the coleoptiles of canary grass, responded to unilateral source of light (phenomenon, known as photoperiodism) by growing towards it., After performing series of experiments, they came to the, conclusion that coleoptile tip was the site that has the, property of transmittable influence due to which bending, of complete coleoptile was caused. The first PGR,, i.e. auxin was isolated by FW Went in 1928, from the, coleoptile tip of oat seedlings., , (a), (c), (b), (d), Experiment used to demonstrate that tip of the coleoptile is the source, of auxin. Arrows indicate direction of light, , 3. Write about the types of auxins., Ans. There are generally two basic categories in which auxins, , are divided, (i) Natural Auxins They occur naturally in plants and, fungi, e.g. Indole Acetic Acid (IAA) and Indole Butyric, Acid (IBA)., (ii) Synthetic Auxins These are prepared from synthetic, compounds that cause several responses to IAA. They, can easily move in all directions inside the plants, e.g., Naphthalene Acetic Acid (NAA), 2, 4dichlorophenoxyacetic acid (2, 4-D)., All these types of auxins are extensively been used in, agricultural and horticultural practices., , 4. Explain inhibitory effect of auxins with the help of, one example., Ans. Higher concentration of auxins inhibits growth of the, , plants. In normal course in nature, self produced auxin, in plants inhibits the growth and development of lateral, buds and as a result lateral bud remains dormant., , 5. In botanical gardens and tea gardens, gardeners, trim the plants regularly, so that they remain, bushy. Does this practice have any scientific, explanation?, (NCERT Exemplar), Ans. The apical buds present in tea and other plants prevent, , the growth of lateral buds in them by releasing auxin, hormone. This phenomenon is called apical dominance., Trimming removes the apical bud and allowing the, lateral buds to grow laterally and give plants a dense, bushy appearance., The scientific explanation for this trimming method is, that apical bud is removed and thus it results in the, removal of auxin and phenomenon of apical dominance, is overcomed., , 6. Auxins are growth hormones capable of promoting, cell elongation. They have been used in, horticulture to promote growth, flowering and, rooting. Write a line to explain the meaning of the, following terms related to auxins., (i) Auxin precursors, (ii) Anti-auxins, (iii) Synthetic auxins, (NCERT Exemplar), Ans. Auxin is an important phytohormone required for the, , growth and development of every plant in its life cycle., (i) Auxin precursors are raw materials required to, initial synthesis of auxins. IAA is synthesised from, tryptophan, adenine compounds and derivatives of, carotenoids., (ii) Anti-auxins are compounds that inhibit action of, auxins, e.g. p-chlorophenoxy isobutyric acid, (PCIB), Tridobenzoic Acid (TIBA), etc., (iii) Synthetic auxins are synthesised not by plants, but, artificially by man, e.g. 2-4 D (weedicide), NAA,, dicamba and IBA (Indole Butyric Acid), which are, natural as well as synthetic auxin., , 7. What are the different applications of auxins in the, field of agriculture and horticulture?, Ans. Use of synthetic auxins is widely accepted now-a-days, , in various agricultural and horticultural practices., Following are the applications of auxins, (i) Eradication of Weeds Auxins are used as, weedicides and herbicides. Application of 2,, 4-dichlorophenoxyacetic acid (2, 4-D) is widely, done in order to kill dicotyledonous weeds. It does, not affect mature, monocotyledonous plants.

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70, , CBSE Term II Biology XI, , (ii) Helps in Cell Division Besides cell elongation,, auxin may also play important role in cell division., (iii) Controls Xylem and Phloem, Differentiation Auxin controls differentiation of, xylem and phloem in stems and roots. There are, evidences that low concentration of auxin induces, phloem differentiation while higher concentration, of auxin is responsible for differentiation of both, xylem and phloem tissues., , 8. Write about the action of auxin on vascular tissue, in plant., Ans. Xylem and phloem are vascular tissue found in plants., , Auxin controls differentiation of xylem and phloem in, stems and roots. There is evidenes that low, concentration of auxin induces phloem differentiation, while higher concentration of auxin is responsible for, differntiation of both xylem and phloem tissues., , 9. Gibberellins were first discovered in Japan when, rice plants were suffering from bakanae (foolish, seedling disease) caused by a fungus Gibberella, fujikuroi., (i) Give two functions of this phytohormone., (ii) Which property of gibberellin caused foolish, seedling disease in rice?, (NCERT Exemplar), Ans., , (i) The functions of hormone, gibberellin, (a) Produce the phenomenon of bolting, i.e. the, growth of the internodal region of stem in, rosette plants., (b) Induces seed germination and break bud and, seed dormancy., (ii) The rice seedling/plant shows excessive growth in, their internodal region when gets infected with, fungus, Gibberella fujikuroi. This fungus produces, excessive amount of plant hormone GA which, makes plants taller than the normal plant foolishly, and many results into death of the plant., , 10. How does spraying of sugarcane plants with, gibberellins increase the yield of sugar?, Ans. Spraying of sugar plants with gibberellin can increase, , the yield of sugar. Spraying increases the length of, internodes and increased or lengthy internodes will, produce more sugar., , 11. Which plant hormone can transform genetically, dwarf plants into tall plants? State the mechanism, involved with suitable example., Ans. Cabbage and sugarbeet plants have rosette habit of, , leaves. The leaves in these plants are condensed, because of shortening of internodal area of the stem. It, is a genetic character. When we spray GA 3 solution on, these plants, these became abnormally tall. It happens, because of increase in internodal area. Thus, such, genetically dwarf plant is made tall by GA 3., , 12. How are gibberellins useful in agriculture to improve, productivity. Give any three points in support of your, answer., Ans. Gibberellins are useful in agriculture in the following ways, , (i) Application of gibberellins increases the length of the, stem and increases the yield of sugar in sugarcane., (ii) Gibberellins delay senescence and prevent the, premature fruits drop., (iii) They can cause fruits like apple to elongate and, improve in shape., , 13. What are the physiological effects of cytokinins?, Ans. Cytokinins have following remarkable physiological effects, , (i) Promotes Cell Division This is one of the most, common and important biological effect of kinetin on, plants, i.e. to induce cell division in the presence of, sufficient amount of auxin (IAA)., (ii) Reduces Apical Dominance They promote the, growth of lateral buds by breaking apical dominance., (iii) Morphogenesis Differentiation or morphogenesis of, plant tissues/organs is seen to be in control, if ratio of, cytokinins and auxins is proportionate., (iv) Resistance They also increase resistance of plants to, high or low temperature and diseases., (v) Delays Senescence These also help in delaying, senescence (ageing) of leaves and other organs by, controlling synthesis of protein and mobilisation of, resources or nutrients., , 14. In an experiment, the callus produced from, internodal segments did not proliferate until coconut, water was added. Give reason., Ans. Callus (i.e. undifferentiated mass of cells) proliferates only, , when nutrient medium containing auxin was supplemented, with coconut milk because it contains kinetin (a cytokinin), which stimulates growth of plant tissues., , 15. Why do cut leaves dipped in cytokinins stay green, for a longer duration?, Ans. Cytokinins are plant growth stimulator, which play a major, , role in cell growth and differentiation. They retard ageing, of plant organ by promoting protein synthesis and, mobilisation of nutrient resources so, the chlorophyll will, be retained and leaves will remain green for longer time., , 16. A farmer grows cucumber plants in his field. He, wants to increase the number of female flowers in, them. Which plant growth regulator can be applied, to achieve this?, (NCERT Exemplar), Ans. Ethylene is also responsible to play a major role in, , determining the sex of monoecious flowers and is, associated with the promotions of femaleness in plants thus, the farmer must spray ethylene hormone on this cucumber, crop to produce female flowers and to increase the yield, (number of fruits produced).

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71, , CBSE Term II Biology XI, , 17. Which PGSs is known as stress hormone and why?, , Ans. Inhibitors are important to the survival of higher plants in, , temperate zones where there are extreme variation in, weather conditions prevails., Here, plants become dormant during harsh winter period, and become active plant on coming favourable conditions., Seeds often will not begin to germinate until they have, been exposed to cold. The breaking of dormancy and the, beginning of growth depend on the release from, inhibition of metabolic activities., , Ans. Abscisic Acid (ABA) is known as stress hormone as it, , reduces rate of transpiration by forceably closing stomata, under the condition of water stress to prevent the plant, from wilting and thus it is called a stress hormone., For example, in deciduous trees, leaves fall down during, autumn when the moisture level in soil reduces and, plants face water stress. ABA thus saves the life of trees, from wilting during drought and desiccation., , 22. On germination, a seed first produces shoots with, , 18. ‘The role of ethylene and abscisic acid is both, , leaves and flowers appear later., (i) Why do you think this happen?, (ii) How is this advantageous to the plant?, , positive and negative’. Justify the statement., Ans. The role of ethylene and abscisic acid is both positive and, , negative. Ethylene is a simple gaseous PGR. It is, synthesised in large amount by tissues undergoing, senescence and ripening. It also promotes senescence, and abscission of plant organs especially of leaves and, flowers. This is its negative effect. As its positive effect,, ethylene breaks seed and bud dormancy, initiates, germination in peanut seeds, sprouting of potato tubers., It promotes internode/petiole elongation in deep water, rice plants. It helps leaves/inner parts of the shoot to, remain above water., Abscisic acid’s positive effect is that it plays an important, role in seed development and maturation. Its negative, effect is that it acts as a genaral plant growth inhibitor and, an inhibitor of plant metabolised. ABA inhibits seed, germination. ABA stimulates the closure of stomata in the, epidermis and increases the tolerance of plants to various, kinds of stresses., , 19. What would be expected to happen if, (i), (ii), (iii), (iv), , GA 3 is applied to rice seedlings., dividing cells stop differentiating., a rotten fruit gets mixed with unripe fruits., you forget to add cytokinin to the culture medium., (NCERT), , Ans., , (i), (ii), (iii), (iv), , Rice seedlings will grow extremely tall., An undifferentiated mass of cells is formed., The unripe fruits will ripe quickly., The callus will not develop shoot buds., , 20. Plant Growth Substances (PGSs) have innumerable, practical applications. Name the PGR you should, use to, (i) increase yield of sugarcane, (ii) promote lateral shoot growth, (iii) cause sprouting of potato tuber, (NCERT Exemplar), (iv) inhibit seed germination, Ans., , (i), (ii), (iii), (iv), , Gibberellin increases yield of sugarcane., Cytokinins promote lateral shoot growth., Gibberellin causes sprouting of potato tuber., Abscisic acid inhibits seed germination., , 21. Suggest some ways in which inhibitors are, important to plant survival in natural adverse, conditions., , (NCERT Exemplar), , (i) On germination, a seed first produces shoots with, leaves, flowers appear later, because the flower, hormone florigen is synthesised in the leaves and is, transmitted to the growing points where flowering, occurs., (ii) It is advantageous to plants as the vegetative phase, prepares the plants for the reproductive phase so, that it can bear structures like fruits and seeds., , Ans., , l, , Long Answer (LA) Type Questions, 1. Explain how the cytokinins, ABA and ethylene, hormones are discovered., , Ans. Discovery of Cytokinins, , F Skoog and his coworkers, studied the nutritional, requirements of tissue culture. They made nutrient, medium derived from the internodal segments of, tobacco stems. They observed that from that internodal, segments, a callus (i.e. a mass of undifferentiated cells), proliferated, only when the nutrient medium containing, auxin was supplemented with the extract of vascular, tissues or yeast or coconut milk (water of endosperm of, coconut)., It was later found that the active substance present in, coconut milk is a modified form of adenine which was, crystallised and identified as kinetin. Further the, compounds that exhibited kinetin like properties were, termed as cytokinins., Discovery of Abscisic Acid, With the progression in the research on plant growth, regulators, three independent researchers reported the, purification and chemical characterisation of three, different kinds of inhibitors (during mid 1960),, i.e. inhibitor B, abscission II and dormin. Later, these, were proved to be chemically identical in nature and, were named as Abscisic Acid (ABA)., Discovery of Ethylene, Cousins (1910), confirmed the release of a volatile, substance from ripened oranges that enhance the, ripening of stored unripened bananas. This volatile, substance was later identified to be a gaseous plant, growth regulator, i.e. ethylene., l, , l

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72, , CBSE Term II Biology XI, , Functions of ethephon are as follows, (i) Ethephon is known to control fruit ripening, (in tomatoes and apples)., (ii) It also helps in accelerating abscission in flowers and, fruits (causes thinning of fruits like cotton, cherry,, walnut, etc)., (iii) Helps in promoting formation of female flowers,, thus, enhancing the yield of the fruits, e.g. cucumber., , 2. Write in detail about abscisic acid., Ans. It is slightly acidic phytohormone that functions as a, , growth inhibitor by counteracting with other mentioned, growth hormones, i.e. auxins, gibberellins and cytokinins., Thus, like other PGR, abscisic acid also has a wide range, of effects on growth and development of plants., As its production is stimulated under stress (unfavourable, conditions such as drought, water lodging, excessive, temperature, etc). So, it is known as stress hormone. It, acts antagonistically to gibberellic acid., Abscisic acid shows various important physiological effects, (i) It has a primary role in regulating abscission and, dormancy of buds and seeds. By inducing dormancy,, it helps the seeds to withstand the desiccation and, other factors related to unfavourable growth., (ii) It acts as a general plant growth inhibitor and also, inhibits metabolism of plants., (iii) It has its role in inhibition of seed germination., (iv) It also plays an important role in seed development, and maturation., (v) Abscisic acid stimulates the closure of stomata., (vi) It promotes senescence by decomposing, chlorophylls, protein and nucleic acid, thus the, leaves turn yellow before falling., , 3. Explain functions and applications of ethylene., Ans. Functions of Ethylene, , Ethylene shows various important physiological effects, (i) In dicot seedlings, ethylene influences the, horizontal growth of seedling, swelling of the axis, and formation of apical hook., (ii) It is highly effective in fruit ripening. It also, increases the rate of respiration. This rise in the, respiration rate is called respiratory climacteric., (iii) It helps in breaking seed and bud dormancy., (iv) Initiation of germination in peanut seeds and, sprouting of potato tubers is also due to the, production of ethylene in plants., (v) In deep water rice plants, ethylene promotes rapid, internode and petiole elongation., (vi) It proves to be helpful in increasing absorption, surface of plants by promoting growth of root and, formation of root hairs., (vii) It also stimulates flowering in fruits like pineapple,, mango and other related plants., Applications of Ethylene, As ethylene helps in regulating these many physiological, processes in plants. It is known to be the most widely, used PGR in agricultural field., Ethephon It is the most widely used compound as a, source of ethylene. This tends to absorb readily in an, aqueous solution and transported within the plant. This, slowly releases ethylene., , 4. Explain why?, (i) Exogenous application of auxin fails to enhance the, growth of intact plants., (ii) Vitamins are not considered as plant growth, hormones., (iii) Some plants, belonging to halophytes and growing, in marshy lands, face great difficulty in seed, germination., (iv) Gibberellins do not enhance the growth of isolated, plant parts., Ans., , (i) Auxin fails to cause growth of intact plants because, the required amount of auxin is already present in, the apical region of such plants and only these parts, grow., (ii) Vitamins have no specific influence on growth of, plants. They are essential dietary factors needed by, an organism in small amounts. They influence on, growth and metabolism through their indirect effect, on metabolism because some vitamins are cofactors, of many enzymes., (iii) Plants belonging to halophytes and growing in marshy, lands, face a great difficulty in seed germination due to, the presence of high concentration of salt in water., These plants solve this problem by vivipary., (iv) Gibberellins require the presence of meristematic cells, to cause elongation growth. Therefore, they do not, enhance growth of isolated plant parts if meristematic, cells are absent., , 5. While experimentation, why do you think it is, difficult to assign any effect seen to any single, hormone?, (NCERT Exemplar), Ans. Most of the hormones are synergistic to each other in, , their mode of functions. Thus, during experimentation, we, cannot judge whether, a particular effect is produced by a, single hormone or is an additive effect of many hormones., For example,, (i) Auxins help to initiate rooting in stem cuttings (an, application widely used for plant propagation)., Cytokinins also show the similar function of root, formation. Auxins promote flowering, e.g. in, pineapples. They also induce parthenocarpy, e.g. in, tomatoes., (ii) Both gibberellins and ethylene are synergistic to, auxin in initiating flowering and for synchronising, fruit set in pineapples.

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73, , CBSE Term II Biology XI, , (iii) Cytokinins and gibberellins help overcome the apical, dominance and delay the process of leaf senescence., (iv) On the other hand, ethylene promotes senescence, and abscission of plant organs especially of leaves and, flowers. This shows that all hormones are synergistic, to each other in their mode of action in plants., , 6. Mention the factors which prove that, phytohormones act synergistically or, antagonistically., Ans. The factors which prove the phytohormones act, , synergistically or antagonistically are, (i) Cell division is promoted by both auxins and, cytokinins acting synergistically., (ii) Auxins and cytokinins interact to control, morphogenetic differentiation of shoot and root., When auxin is in excess, roots differentiate on the, callus, while excess of cytokinins promotes shoot bud, formation., (iii) Auxins and cytokinins act antagonistically in, controlling apical dominance. Auxins cause apical, dominance, while cytokinins overcome same., (iv) Senescence is prevented by auxin and cytokinin,, while it is stimulated by abscisic acid., (v) The activity of cambium and fruit growth seems to be, promoted by auxins, gibberellins and cytokinins, the, same is inhibited by abscisic acid., (vi) The dormancy of seeds and buds is mostly due to, abscisic acid and the same is broken by gibberellins., (vii) Cytokinins cause opening of stomata, while abscisic, acid results in their closure., l, , Case Based Questions, 1. Direction Read the following passage and answer, the questions that follows., Raju’s father is a businessman, they have many, orchards. On one fine sunday, he went to a mango, orchard, where he saw that some workers were, placing carbide powder in between the raw mangoes, before covering them. He asked one of the worker,, why do they do so and what will be its effect on, mangoes. Then, the worker showed him another, carten in which he placed the same powder. Few, days ago, Raju was surprised to see that all mangoes, are riped and their skin colour is also changed due to, this, worker explained that this powder helps the, fruits in ripening., (i) How does the carbide powder help in ripening of, mangoes?, , Ans. The carbide powder contains ethylene hormone which, , helps in ripening of mangoes., , (ii) What is respiratory climacteric?, Ans. The rise of the rate of respiration in ripening of fruits is, , called respiratory climacteric., , (iii) Which is the most widely used PGR in agriculture, and why?, Ans. Ethylene is the most widely used PGR in agriculture as, , it regulates many physiological processes like inducing, flowering, synchronise fruit set, etc., , (iv) Name the most widely used source of ethylene., Ans. Ethephon is the most widely used compound as a source, , of ethylene., , (v) Where does the plant hormone ethylene is, synthesised in plants?, Ans. Ethylene is synthesised in the tissues undergoing, , senescence and ripening fruits., , 2. Direction Read the following passage and answer, the questions that follows., Phytohormones play vital roles in the growth and, development of plants as well as in interactions of, plants with microbes. These are naturally, occurring small organic substances which are, generally active at very low concentration and, often, impose inhibitory effects if applied or, present at higher concentration. The five classical, phytohormones are auxins, cytokinins,, gibberellins, abscisic acid and ethylene. These, hormones produce various effects in plants like, phototropism, bolting, dormancy, abscission, etc., They also have synergistic and antagonistic, functions in various processes., (i) Which hormone induces phototropism and, geotropism in plants?, Ans. Auxins are responsible for phototropism and geotropism, , in plants., , (ii) What is precursor of gibberellins?, Ans. Acetyl Co-A is the precursor of gibberellins. These are, , synthesised via the mevalonic acid pathway., , (iii) In which part of plant, high concentration of auxin, is present?, Ans. High concentration of auxin is present in the growing, , apices of the stem, from where auxin migrates to its, regions., , (iv) Which plant hormone is found in gaseous form?, Ans. Ethylene is found in gaseous form., , (v) Which hormone is used to speed up the malting, process?, Ans. GA 3 is used to speed up the malting process in brewing, , industries.

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Chapter Test, Multiple Choice Questions, , 1. Assertion (A) Gibberellins induce elongation of, genetic dwarfism in maize., , 1. Identify the correct statement., (a) PGR has diverse physiological effects on plants, (b) PGR may act synergistically or antagonistically, (c) Two PGRs can have same effect, (d) All of the above, , 2. Widely different organisms such as plant and fungi, contain how many types of gibberellins?, (a) More than 50, (b) More than 75, (c) More than 100, (d) More than 25, , 2. Assertion (A) Kinetin is found naturally in plants., Reason (R) Cytokinins do not break seed and bud, dormancy., , 3. Assertion (A) Ethylene synthesis increases in case of, wounds and thus help in wound healing., Reason (R) Ethylene causes tropic response in plants., , Short Answer Type Questions, , 3. Length of grapes stalks increases due to, (a) auxin, (c) gibberellins, , 4., , Reason (R) GA3 reduces α-amylase synthesis in, seeds., , (b) cytokinins, (d) ethylene, , I. Leaf abscission is ... A ... by auxin in younger leaves and, fruits., II. Apical dominance is ...B... by auxin., , Identify A and B from the options given below., (a) A–inhibited, B–promoted, (b) A–inhibited, B–inhibited, (c) A–promoted, B–promoted, (d) A–promoted, B–inhibited, , 1. What are plant growth hormones? How do they, differ from plant growth regulators?, , 2. How do IBA and 2, 4-D are used in agriculture?, 3. What conditions can induce the phenomenon of, bolting naturally and how can it be induced, artificially?, , 4. Fill in the blanks., (i) ................ is a simple gaseous hormone., (ii) ............... is shedding of leaves, fruits or flowers by a, plant., , 5. Which combination of hormones can be applied to, artificially induce flowering in pineapple plants, throughout the year to increase yield?, (a) Auxin and ethylene, (b) Gibberellin and cytokinin, (c) Gibberellin and abscisic acid, (d) Cytokinin and abscisic acid, , (iii) Plant growth is generally confined to ................, regions and in ................ tissues., (iv) Cytokinins are synthesised in areas where ................ is, occurring., , 5. Give one antagonistic function of each of the, following hormone pairs., , Assertion-Reasoning MCQs, Direction (Q. Nos. 1-3) Each of these questions contains two, statements, Assertion (A) and Reason (R). Each of these, questions also has four alternative choices, any one of, which is the correct answer. You have to select one of the, codes (a), (b), (c) and (d) given below., (a) Both A and R are true and R is the correct explanation of A, (b) Both A and R are true, but R is not the correct explanation, of A, (c) A is true, but R is false, (d) A is false, but R is true, , (i) Gibberellins, , — Abscisic acid, , (ii) Cytokinin, , — Ethylene, , (iii) Abscisic acid — Auxin, , Long Answer Type Questions, , 1. (i) Name the cytokinin like substance isolated from, corn kernels and coconut milk., , (ii) How gibberellins are different from auxins?, , 2. (i) What will you do to prevent leaf and fruit drop in, plants? Support your answer with reason., (ii) Write a note on ethephon., , Answers, Multiple Choice Questions, 1. (d), , 2. (c), , 3. (c), , 4. (a), , Assertion-Reasoning MCQs, 1. (c), , 2. (d), , 3. (c), , 5. (a), , For Detailed Solutions, Scan the code

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75, , CBSE Term II Biology XI, , CHAPTER 05, , Breathing and, Exchange of Gases, In this Chapter..., , l, , l, , l, , l, , l, , l, , l, , Exchange of Gases, , l, , Respiratory Organs, , l, , Transport of Gases, , l, , Human Respiratory System, , l, , Regulation of Respiration, , l, , Mechanism of Breathing, , l, , Disorders of Respiratory System, , Respiration is an oxidative process involving the oxidation, of food substances such as carbohydrates, fats and proteins, within the tissues to form CO2 , water and consequent, release of energy., The respiratory system provides the route by which the, oxygen present in our environment gains entry into the, body and the carbon dioxide is excreted. This whole, process of exchange of gases is called breathing., , Respiratory Organs, l, , l, , Different animal groups have evolved different, mechanisms of breathing for the exchange of gases., Lower animals like sponges, cnidarians, platyhelminths and, free-living roundworms exhange O2 by simple diffusion, through body surface., Earthworms respire through moist cuticle and insects have, a network of tubes (tracheal tubes) to transport atmospheric, air within the body., Special vascularised structures called gills (branchial, respiration) are used by most of the aquatic arthropods and, molluscs., The highly vascularised bags called lungs (pulmonary, respiration) are used by the terrestrial forms for the, exchange of gases, e.g. reptiles, birds and mammals., Amphibians (frog) respire through their skin (cutaneous, respiration) as well as lungs., , Human Respiratory System, Human respiratory system may be divided into two major, components, i.e. conduction of gases and respiration or, exchange of gases., , Conduction of Gases, It is the passage for the air (transports the atmospheric air to, the lung alveoli and return from lungs to the exterior). This, portion clears air by removing foreign particles, humidifies it, and also brings it to body temperature. In this part, gaseous, exchange does not take place. It is also called dead air space., It starts with the external nostrils upto the terminal, bronchioles., The various parts are as follows, (i) External Nares (Nostrils) There is a pair of slits at the, lower end of the nose, which opens into the nasal, chamber through the nasal passage., (ii) Nasal Chambers Pair of passage located at the back of, nostrils just above the mouth cavity. Nasal septum is a, median partition that separates the two chambers., Each chamber has three regions, i.e. vestibular,, respiratory and olfactory. The chambers has special, pseudostratified ciliated epithelium by which air is, filtered (by hairs) and moistened (by mucus)., (iii) Internal Nares These are the posterior openings of the, nasal chambers that lead into the nasopharynx.

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76, (iv) Nasopharynx It is the upper part of pharynx, into, which internal nares open., (v) Larynx It is the upper part of trachea. It allows the, air to pass into lungs. Nasopharynx opens through, glottis of the larynx into trachea. Glottis is a slit-like, aperture that remains open except during swallowing., The glottis bears a leaf-like cartilaginous flap, the, epiglottis at its anterior region. It closes the glottis to, check the entry of food during swallowing. Larynx, helps in sound production and hence, called the, sound box., Note Larynx is often called the Adam’s apple and is more prominent in, men than in women., , CBSE Term II Biology XI, , l, , l, , pulmonary cavity. This arrangement is necessary for, breathing as the pulmonary volume cannot be altered, directly., Each lung is enclosed by two membranes called the pleura, (layers of peritoneum of the thorax). The inner membrane,, called the visceral pleuron, which is firmly bound to the, surface of lungs. The outer membrane, called the parietal, pleuron is held to the thoracic wall and diaphragm by, connective tissue., Pleural cavity is a very narrow space that exists between the, two pleura. It contains the pleural fluid secreted by the, pleura, for reducing friction on the lung surface., Epiglottis, , (vi) Trachea It is a thin-walled tube, about 11 cm long, and 2.5 cm wide. It extends up to the mid-thoracic, cavity. It passes the air to the alveoli., , Respiratory/Exchange of Gases, The alveoli and their ducts form this part of the respiratory, system. It is the site of actual diffusion of O2 and CO2, between blood and atmospheric air. The branching network, of bronchi, bronchioles and alveoli comprises the lungs,, which provide the surface for exchange of gases in humans., Lungs, l, , l, , l, , Humans have two lungs one at right and other on left, side in chest region. These are triangular bags that, constitute the respiratory organ and are site for gaseous, exchange ( O2 / CO2 )., They lie in the thoracic cavity on the sides of the heart., It is an anatomically airtight chamber. The thoracic cavity, is enclosed dorsally by thoracic vertebrae, laterally by, the ribs, ventrally by the sternum and closed below by a, dome-shaped diaphragm., The arrangement of lungs is such that any change in the, volume of thoracic cavity will be manifested in the, , Bronchus, , Cut end, of rib, , heart, , (vii) Primary and Secondary Bronchi At the level of 5th, thoracic vertebra, the trachea divides into two tubes,, right and left primary bronchi., Each bronchi further divides into secondary bronchi., The secondary bronchi subdivides into smaller tertiary, bronchi, which is further divided into still smaller, bronchioles. The small terminal bronchioles give off a, number of thin, irregular walled, one cell thick,, vascular bag-like structure called lung alveoli., Cartilaginous rings support the walls of the trachea, and the bronchi to prevent their collapse. Each, terminal bronchiole gives rise to a number of thin, irregular walled and vascularised bag-like structure, called alveoli. The branching network of bronchi,, bronchioles and alveoli form the lungs., , Larynx, Trachea, Parietal pleura, , Right lung, Diaphragm, , Visceral pleura, Cardiac notch, Pleural membranes, Alveoli, Pleural fluid, Bronchiole, , Diagrammatic view of human respiratory system, (sectional view on the left side), , External Features of Lungs, (i) The left lung has two lobes, i.e. superior lobe and inferior, lobe separated by oblique fissure. It has a cardiac notch, a, concave cavity where the heart lies. It is longer and, narrower than right lung., (ii) The right lung is bigger and has three lobes, i.e. superior, lobe, middle lobe and inferior lobe separated by, horizontal fissure and oblique fissure., , Respiration Processes : Breathing, and Gaseous Exchange, The main mechanism of respiration is categorised into, following three steps, (i) Breathing (pulmonary ventilation) is the inflow of, atmospheric air and release (outflow) of CO2 rich, alveolar air., (ii) Exchange of gases (O2 and CO2 ) across alveolar, membrane as well as in tissues., (iii) Transport of gases by the blood., , Breathing, Breathing is an extracellular, energy consuming and physical, process. It involves movement of thorax, expansion (inflation), and deflation of lungs and flow of air into and from the lungs by, creating a pressure gradient between the lungs and the, atmosphere.

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77, , CBSE Term II Biology XI, , The movement of diaphragm and a specialised set of muscles, (i.e. external and internal intercostals between the ribs) help, in generation of such difference of pressure gradients, between lungs and atmosphere. Breathing mainly involves, two steps, , Contraction of diaphragm and external intercostal muscles, Air entering lungs, , Ribs and sternum, raised, , Volume of thorax, increased, , 1. Inspiration, It is an active process by which fresh air enters the lungs. It, can occur if the pressure within the lungs (intrapulmonary, pressure) is less than the atmospheric pressure, i.e., negative pressure in lungs with respect to atmospheric, pressure., Following muscles play an important role, (a) Diaphragm It is lowered by the contraction of its, muscle fibres and becomes flat. This causes an increase, in the volume of thoracic chamber in the, antero-posterior axis., (b) External Intercostal Muscles They occur between the, ribs (internal intercostal muscles are related to, expiration). The external intercostal muscles contract, and pull the ribs and the sternum upward and outward, thus, increasing the volume of thoracic chamber in, dorsoventral axis., Thus, the overall increase in the volume of thoracic cavity, causes an increase in pulmonary volume. As a result, there, is a decrease in the intrapulmonary pressure. The greater, atmospheric pressure outside the body now causes air to, flow rapidly into external nares, which sequentially leads to, alveoli., From the alveoli, O2 passes into blood of the capillaries and, CO2 diffuses out from blood to alveoli’s lumen., , Diaphragm, contracted, (a), Relaxation of diaphragm and external intercostal muscles, Air expelled from lungs, , l, , Ribs and sternum, returned to original, position (lowered), , l, , l, , l, , It is a passive process by which CO2 is expelled out from, the lungs. It takes place when the intrapulmonary pressure, is higher than the atmospheric pressure., The movements of muscles involved in the breathing, mechanism are as follows, (a) Diaphragm The muscle fibres of the diaphragm relax, making it convex, decreasing volume of the thoracic, cavity., (b) Internal Intercostal Muscles These muscles contract, thus, pulling the ribs downward and inward, decreasing, the thoracic volume., The overall volume of the thoracic cavity thus, decreases, thereby reducing the pulmonary volume. As a result, the, intrapulmonary pressure increases slightly above the, atmospheric pressure. This in turn causes the expulsion of, the air from the lungs. The process of expiration is simpler, than inspiration., , Volume of thorax, decreased, Lungs return to, original position, Diaphragm, relaxed, and arched, upwards, , (b), , Mechanisms of breathing showing, (a) Inspiration, (b) expiration, , l, , 2. Expiration, , Lungs expanded, , Rib cage, , l, , Respiratory Volumes and Capacities, l, , l, , The quantity of air, the lungs can receive, hold or expel, under different conditions are called respiratory, (pulmonary) volumes. Combination of two or more, pulmonary volumes are called respiratory (pulmonary), capacities., Different types of respiratory volumes and respiratory, capacities are tabulated below, Respiratory Volumes, , Tidal volume, , Volume of air inspired, or expired during a, normal respiration, , 500 mL, , Inspiratory, Reserve, Volume (IRV), , Additional volume of, air, a person can inspire, by a forcible inspiration, , 2500-3000 mL, , Expiratory, Reserve, Volume (ERV), , Additional volume of, air, a person can expire, by a forcible expiration, , 1000-1100 mL, , Residual, Volume (RV), , Remaining volume of, air in lungs after a, forcible expiration, , 1100-1200 mL, , Respiratory Capacities, Inspiratory, Capacity (IC), , Total volume of air, a, person can inspire after, normal expiration, , TV+IRV, = 3500 mL

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78, , CBSE Term II Biology XI, , Tidal volume, , Volume of air inspired, or expired during a, normal respiration, , 500 mL, , Expiratory, Capacity (EC), , Total volume of air, a, person can expire after, normal inspiration, , TV + ERV, = 1600 mL, , Functional, Residual, Capacity, (FRC), , Volume of air that will, remain in lungs after, normal expiration, , ERV + RV, = 2300 mL, , Vital, Capacity, (VC), , Maximum volume of air,, a person can breathe, after forced expiration, , ERV + TV +, IRV, = 4600 mL, , Total Lung, Capacity, (TLC), , Total volume of air, accommodated in the, lungs at the end of a, forced inspiration, , VC + RV or RV, + ERV + TV +, IRV, = 5800 mL, , can diffuse through the membrane per unit difference in, partial pressure is much higher as compared to oxygen., To pulmonary vein, Air, Alveolar wall, (one-celled thick), , l, , l, , l, , This exchange between lung alveoli and pulmonary, capillaries is called external respiration., The alveolar wall is very thin with a rich network of blood, capillaries. It is also called as respiratory membrane, (alveolar-capillary membrane)., (a) Alveolar epithelium, (b) Epithelial basement membrane, (c) Their interstitial space, (d) Capillary basement membrane, (e) Capillary endothelium, All these form a membrane of about 0.2 mm thickness., This membrane has a limit of gaseous exchange between, alveoli and pulmonary blood. It is called diffusing, capacity. It is the volume of gas that diffuses through, membrane per minute for a pressure difference of, 1 mm Hg., At a particular pressure difference, the diffusion of CO2 is, 20-25 times faster than oxygen. Thus, the amount of that, , Red blood cells, O2 enters blood, , Blood, capillary, , CO2 enters alveolus, , A diagram of a section of an alveolus with the pulmonary, capillary, l, , Partial pressures (in mm Hg) of oxygen and carbon dioxide, at different parts involved in diffusion in comparison to, those in atmosphere are as follows, , Respiratory AtmospGas, heric Air, , l, , Blood, Blood, AlveTissues, (Deoxyge, (Oxygenated), oli, nated), , O2, , 159, , 104, , 40, , 95, , 40, , CO2, , 0.3, , 40, , 45, , 40, , 45, , As seen in the above table, pO2 in the alveoli (104 mmHg), is higher than that in the deoxygenated blood in the, capillaries of pulmonary arteries (95 mmHg). So, there is, diffusion of O2 from alveoli to the blood capillary. Also,, pCO2 is higher in deoxygenated blood (45 mmHg) than in, alveoli, therefore CO2 diffuses from blood to the alveoli., , 1. Exchange of Gases between, Alveoli and Blood, l, , Alveolar cavity, , From, pulmonary, artery, , Exchange of Gases, The primary sites for exchange of gases are the alveoli and, tissues. It occurs by simple diffusion mainly based on, pressure/concentration gradient., The factors that affect rate of diffusion are, (i) Thinness of the membrane., (ii) Surface area of the membrane., (iii) Permeability of the membrane., (iv) Solubility of the gases., (v) Partial pressure gradient (difference) of gases on the, two sides of the diffusing surfaces of lung alveoli., , Basement substance, , Inspired air Expired air, Alveolar air, , Blood entering, pO2=104mmHg, alveolar capillaries pCO =40mmHg, 2, CO2 O2, Pulmonary, artery, , Systemic veins, (carrying, deoxygenated, blood), pO2 =40 mmHg, pCO2=45 mmHg, , Alveolus, Blood entering, alveolar capillaries, , CO2 O2, Pulmonary vein, , CO2 O2, , Systemic arteries, (carrying oxygenated blood), pO2 =95 mmHg, pCO2=40 mmHg, , CO2 O2, Body tissues, , Diagrammatic representation of exchange of gases at the alveolus, and the body tissues with blood and transport of oxygen and carbon, dioxide

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79, , CBSE Term II Biology XI, , l, , l, , This exchange between tissue blood capillaries and, tissue cells is called internal respiration. pO2 in, oxygenated blood (95 mmHg) > pO2 in body cells, (40 mmHg) and pCO2 in oxygenated blood, (40 mmHg) < pCO2 in body cells (45 mmHg)., Due to this partial pressure differences, oxygen, diffuses from the capillary blood to the body cells and, CO2 diffuses from the body cells to the capillary blood, via tissue fluid. Now, the blood becomes, deoxygenated, which is further carried to the heart by, veins and finally it goes to lungs for purification., , Transport of Gases, Blood carries oxygen from the lungs to tissue cells for, oxidation and carbon dioxide from the tissue cells to the, respiratory surface for elimination., Transport of oxygen and carbon dioxide in detail is, discussed below, , Transport of Oxygen, l, , l, , It is done in the following manner, (i) As Dissolved Gas About 3% of oxygen in the blood, is carried in a dissolved state through the plasma., (ii) As Oxyhaemoglobin About 97% of O2 is carried by, RBCs in the blood., Haemoglobin is a red coloured iron containing, pigment present in RBCs to which O2 can bind in a, reversible manner to form oxyhaemoglobin. Four, molecules of oxygen bind one molecule of, haemoglobin., Hb, Haemoglobin, , l, , + O2, , In lungs, , HbO2, Oxygen In tissues Oxyhaemoglobin, , f, , Factors affecting the binding of oxygen with, haemoglobin are, (i) Partial pressure of oxygen, (ii) Partial pressure of carbon dioxide, (iii) Hydrogen ion concentration, (iv) Temperature, , Oxygen Dissociation Curve or, Oxyhaemoglobin Dissociation Curve, It is the curve obtained on plotting percentage saturation, of Hb with O2 against pO2 ., , The curve thus, obtained is sigmoid shaped or S-shaped, under, normal conditions., (i) This curve is useful in studying the effect of factors like, pCO2 , H + concentration and temperature, etc., on binding, of O2 with Hb., (ii) The lower part of the curve indicates dissociation of oxygen, from haemoglobin, while the upper part of the curve, indicates the acceptance of O2 by Hb., , Percentage saturation of, haemoglobin with oxygen, , 2. Exchange of Gases between Blood, and Tissue Cells, , 100, , Shift to left at low, pCO2 and low, temperature, , 80, , Shift to right at, high pCO 2 and, high temperature, , 60, 50, 40, 20, , 0, , P50, , 20 27 40, 60, 80, 100, Partial pressure of oxygen (mm Hg), Oxygen dissociation curve, , (iii) The oxygen haemoglobin dissociation curve is shifted either, to left or right by various factors., Shift to left indicates association of O2 by Hb. It occurs in, the alveoli where there is low pCO2 , high pO2 , lesser H +, concentration and low temperature., Note In the foetal blood, there is a shift to left because foetal haemoglobin, has more affinity for oxygen than the adult Hb., , (iv) Shift to right indicates dissociation of O2 from Hb. It, occurs in the tissues where there is low pO2 , high pCO2 ,, low pH (high H + concentration and higher temperature)., (v) This clearly indicates that O2 gets bound to Hb on the lung, surface and gets dissociated at the tissue level., (vi) Every 100 mL of oxygenated blood can deliver around, 5 mL of O2 to the tissues under normal physiological, conditions. People feel difficulty in breathing at hills, because air pressure falls there at hills. So, less oxygen is, diffused to lung blood vessels., , Transport of Carbon Dioxide, CO2 in gaseous form diffuses out of the cells into capillaries,, where it is transported in following ways, (i) Transport in Dissolved Form About 7% CO2 is carried in, dissolved form through the plasma because of its high, solubility.

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80, , CBSE Term II Biology XI, , (ii) Transport as Bicarbonate The largest fraction (about, 70%) is carried in plasma as bicarbonate ions (HCO −3 ). At, the tissues site, where pCO2 is high due to catabolism,, CO2 diffuses into the blood (RBCs and plasma) and forms, HCO −3 and H + ., Carbonic, , CO2 + H2 O, Carbon, dioxide, , HCO −3, anhydrase Bicarbonate, ion, , r, , +, , H+, Hydrogen, ion, , This reaction is faster in RBCs because they contain an, enzyme carbonic anhydrase. Hydrogen ion released, during the reaction bind to Hb, triggering the Bohr’s, effect., At the alveolar site, where pCO2 is low, the reaction, proceeds in opposite direction forming CO2 and H2 O. Thus,, CO2 trapped as bicarbonate at tissue level and transported to, alveoli is released as CO2 ., Hamburger’s phenomenon, This is the phenomenon in which an exit of bicarbonate ions, considerably changes ionic balance between the plasma and, erythrocytes. This ionic balance is restored by the diffusion of, chloride ions from the plasma into the erythrocytes., , (iii) Transport as Carbaminohaemoglobin Nearly 20-25%, CO2 is carried by haemoglobin as, carbaminohaemoglobin. CO2 entering the blood, combines with the NH2 group of the reduced Hb., , rHbCO, , 2, , The respiratory rhythm can be maintained and moderated by, human beings to suit the demands of the body tissues. It is, under dual control, i.e. nervous and chemical. This is, explained below as, , i. Neural Control, , -, , H2 CO 3, anhydrase Carbonic, acid, Carbonic, , HbO2 + CO2, , Regulation of Respiration, , + H + + O2, , (Carbaminohaemoglobin), , The reaction releases oxygen from oxyhaemoglobin. Factors, affecting the binding of CO2 and Hb are, (i) Partial pressure of CO2 ., (ii) Partial pressure of O2 (major factor)., In tissues, pCO2 is high and pO2 is low, more binding, of CO2 occurs while, in the alveoli, pCO2 is low and, pO2 is high, dissociation of CO2 from HbCO2 takes, place, i.e. CO2 which is bound to Hb from the tissues, is delivered at the alveoli., Every 100 mL of deoxygenated blood delivers, approximately 4 mL of CO2 to the alveoli., Haldane effect states that binding of oxygen with Hb, tends to displace CO2 from the blood. It is, quantitatively more important in promoting CO2, transport than the Bohr effect in promoting O2, transport. Thus, Haldane effect and Bohr effect, complement each other., , The respiratory rhythm centre is composed of a group of, neurons located in the medulla oblongata and pons Varolii., Pons Respiratory Centres, l, , l, , l, , Neural signal from pneumotaxic centres reduce the, duration of inspiration, altering the respiratory rate., A chemosensitive area is located adjacent to rhythm centre, that is highly sensitive to CO2 and hydrogen ions. They, increase activity of this centre, which in turn signals the, respiratory centre to make necessary changes in order to, eliminate these substances., Oxygen does not have a significantly direct effect on the, respiratory centre of the brain in controlling respiration., , ii. Chemical Control, l, , l, , Large number of chemoreceptors are located in the carotid, bodies, which lie bilaterally in the bifurcations of the, common carotid arteries. Their afferent nerve fibres pass, through glossopharyngeal cranial nerve and thus, to dorsal, respiratory area of the medulla oblongata., Receptors of aortic arch and carotid artery recognise, change in CO2 and H + concentration and send necessary, signals to the rhythm centre for remedial actions., , Disorders of Respiratory System, Common respiratory disorders are tabulated below, Disorders, Asthma, , Characteristics, l, l, , l, , Emphysema, , l, , l, l, , Occupational, respiratory, disorder, , l, , l, l, , Difficulty in breathing caused due to allergens., Wheezing due to the inflammation of bronchi, and bronchioles., Can be prevented by avoiding and treated by, using inhalers., Decreased respiratory surface due to damaged, alveolar walls., Mainly caused due to cigarette smoking., Avoiding cigarettes can be preventive, measures., Mainly caused due to long exposure to, grinding or stone breaking., Inflammation leading to fibrosis of lungs., Protective masks can reduce the risk.

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81, , CBSE Term II Biology XI, , Chapter, Practice, PART 1, Objective Questions, l, , Multiple Choice Questions, 1. Over the entire body surface, O 2 exchange with CO 2, by simple diffusion occurs in, (a) sponges, (b) coelenterates, (c) flatworms, (d) All of these, (d) Breathing mechanism varies among the different groups, of animals depending on their habitats and level of, organisation. Lower invertebrates like sponges,, coelenterates, flatworms, etc., exchange air through simple, diffusion over their entire body surface., Thus, option (d) is correct., , 2. Which of the following statements is correct about, respiratory organs of different animals?, (a) The exchange of O2 and CO2 via simple diffusion across, body surface occurs in aquatic arthropods, (b) A complex system of air tubes called trachea is present in, earthworm for respiration, (c) Fishes have lungs for respiration, (d) Cutaneous respiration occurs in amphibians, (d) Statement in option (d) is correct., , (a) Statement in option (a) is incorrect and can be, corrected as, Each terminal bronchiole gives rise to a network of, alveoli., Rest other statements are correct., , 5. Which of the following changes occurs in, diaphragm and intercostal muscles when, expiration of air takes place?, (a) External intercostal muscles relax and diaphragm, contracts, (b) External intercostal muscles contract and, diaphragm relaxes, (c) External intercostal muscles and diaphragm relax, (d) External intercostal muscles and diaphragm, contract, (c) During expiration, muscle fibres of the diaphragm, and external intercostal muscles get relaxed., , 6. Match the items given in Column I with those in, Column II and select the correct option given, below., , 3. Conducting part of the respiratory system comprises, (a) external nostrils upto the terminal bronchioles, (b) internal nostrils upto trachea, (c) epiglottis upto trachea, (d) larynx upto bronchi, (a) The conducting portion of the respiratory system consists, of nasopharynx, larynx, trachea, bronchi, bronchioles and, terminal bronchioles, i.e. all structures from external nostrils, upto terminal bronchioles., , 4. Which of the following statements is incorrect, regarding respiratory system?, (a) Each terminal bronchiole gives rise to a network of, bronchi, (b) The alveoli are highly vascularised, (c) The lungs are covered by a double-layered membrane, (d) The pleural fluid reduces friction on the lung surface, , Column I, (Lung Volume), , Column II, (Value), , A., , Tidal volume, , 1., , 2500-3000 mL, , B., , Inspiratory reserve, volume, , 2., , 1100-1200 mL, , C., , Expiratory reserve, volume, , 3., , 500 mL, , D., , Residual volume, , 4., , 1000-1100 mL, , Codes, A B C D, (a) 1 4 2 3, (b) 3 1 4 2, (c) 3 2 1 4, (d) 4 3 2 1, (b) A–3, B–1, C–4, D–2

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82, , CBSE Term II Biology XI, , 7. In the given diagram of mechanism of breathing,, , what do A , B and C depict?, A, , B, , Volume of thorax decreased, , C, , (a) A–Air goes inside to lungs, B–Ribs and sternum, returned to original position, C– Diaphragm, contracted, (b) A–Air expelled from lungs, B–Ribs and sternum, returned to original position, C–Diaphragm relaxed and, arched upward, (c) A–Air expelled from lungs, B–Ribs and sternum go, upward, C–Diaphragm relaxed and arched upward, (d) A–Air goes inside to lungs, B–Ribs and sternum go, upward, C–Diaphragm relaxed and arched upward, (b) When air is expelled from the lungs (label A), the, internal intercostal muscles contract which pulls the ribs, and sternum downward and inward, i.e. original position, (label B). Also, the muscle fibres of the diaphragm relax, which decreases the thoracic volume and makes the, diaphragm arched upward (label C)., Thus, option (c) is correct., , 8. Consider the following statements., I. The partial pressure of oxygen in deoxygenated, blood is 40 mmHg., II. The partial pressure of oxygen in oxygenated blood, is 95 mmHg., III. The partial pressure of oxygen in alveolar air is, 104 mmHg., IV. The partial pressure of CO2 in the atmospheric air, is 40 mmHg., , Choose the option containing incorrect statement(s), only., (a) I and III, (b) Only IV, (c) Only II, (d) III and IV, (b) Statement IV is incorrect and can be corrected as, The partial pressure of CO2 in deoxygenated blood is, 40 mmHg while in atmospheric air, pCO2 is 0.3 mmHg., Rest other statements are correct., , 9. What is Bohr’s effect?, (a) A rise in levels of pCO 2 or fall in pH decreases the, oxygen affinity of haemoglobin, (b) Decrease in levels of pCO 2 or fall in pH decreases, the oxygen affinity of haemoglobin, (c) A rise in levels of pCO 2 or increase in pH decreases, the oxygen affinity of haemoglobin, (d) Shifting of the oxygen-haemoglobin curve to left, (a) Bohr's effect is described as a rise in pCO 2 (or fall in, pH) which decreases the oxygen affinity of haemoglobin, thus, raising the P50 value and shifts the curve to the, right., , 10. Partial pressure of O 2 and CO 2 in atmospheric air, as compared to that in alveolar air is, pO 2, , pCO 2, , (a) Higher, Lower, (b) Higher, Higher, (c) Lower, Lower, (d) Lower, Higher, (a) The pO2 is higher in the atmosphere as compared to, alveoli and pCO2 is lower in the atmosphere as, compared to alveoli., , 11. Consider the following statements., I. The percentage of haemoglobin that is bound, with haemoglobin is called per cent saturation of, haemoglobin., II. Every 100 mL of oxygenated blood can deliver, 60 mL O 2 to the tissues under normal conditions., III. P 50 value is the value of O 2 at which Hb is 50%, saturated with oxygen., IV. Unlike haemoglobin, myoglobin has three, polypeptide chains., , Choose the option containing incorrect statements., (a) I and III, (b) II and IV, (c) III and IV, (d) I and II, (b) Statements II and IV are incorrect and can be, corrected as, 100 mL arterial blood carries about 19-20 mL of, oxygen but it delivers 4-6 mL of oxygen at tissue level, in normal conditions., Unlike Hb, myoglobin contains only one polypeptide, chain., Rest other statements are correct., l, , l

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83, , CBSE Term II Biology XI, , 12. When you hold your breathe, which of the following, gas changes in blood would first lead to the urge to, breathe?, (a) Falling CO 2 concentration, (b) Rising O 2 concentration, (c) Falling O 2 concentration, (d) Rising CO 2 concentration, (d) Rising CO2 concentration will lead to urge to breathe,, this is because CO2 is toxic to human body and needs to, be excreted., , 13. Which of the following statements is incorrect about, the given graph?, , Assertion-Reasoning MCQs, Direction (Q. Nos. 1-5) Each of these questions contains, two statements, Assertion (A) and Reason (R). Each of, these questions also has four alternative choices, any one, of which is the correct answer. You have to select one of, the codes (a), (b), (c) and (d) given below., (a) Both A and R are true and R is the correct, explanation of A, (b) Both A and R are true, but R is not the correct, explanation of A, (c) A is true, but R is false, (d) A is false, but R is true, , 1. Assertion (A) Trachea and bronchioles are, , 100, , A, , l, , supported by cartilaginous ring., , 80, , Reason (R) Trachea can collapse during expiration., , 60, , (c) A is true, but R is false because, Trachea and initial bronchioles are supported by, incomplete cartilaginous rings. These support the trachea, and prevent it from being collapsed during breathing., , 40, 20, , 2. Assertion (A) Expiration is a passive process., 0, 20, , 40, , 60, B, , 80, , 100, , (a) The curve is called oxygen dissociation curve, (b) The part A represents percentage saturation of, haemoglobin with oxygen, (c) The part B represents partial pressure of carbon, dioxide, (d) This curve is highly useful in studying the effect of, factors like pCO2 , H+ concentration, etc., (c) Statement in option (c) is incorrect about the given, graph. It can be corrected as, The part B represents partial pressure of oxygen., , 14. Pneumotaxic centre of the brain, i.e. pons region can, (a) moderate the function of respiratory system, (b) decrease the heart rate, (c) increase the heart rate, (d) increase the flow of blood, (a) Respiratory centre present in the pons region of the, brain is called pneumotaxic centre. It can moderate the, functions of respiratory rhythm centre. Neural signal, from this centre can reduce the duration of inspiration and, thereby, alter the respiratory rate., , 15. Name the pulmonary disease in which alveolar, , surface area involved in gas exchange is drastically, reduced due to the damage in the alveolar walls., (a) Pleurisy, (b) Emphysema, (c) Pneumonia, (d) Asthma, (b) Emphysema or inflation of alveolar sacs involves, collapse of alveolar septa as a result of which the area for, gaseous exchange is reduced and there is difficulty in, breathing., , Reason (R) It occurs when the intrapulmonary, pressure is higher than the atmospheric presssure., (b) Both A and R are true, but R is not the correct, explanation of A., Expiration is a passive process since air leaves the lungs, without using energy., It occurs when intrapulmonary pressure is higher than, the atmospheric pressure., , 3. Assertion (A) High carbon monoxide (CO) levels, , can kill a person., Reason (R) CO has greater affinity for, haemoglobin., (a) Both A and R are true and R is the correct explanation, of A., Carbon monoxide combines with haemoglobin far readily, as compared to oxygen, since it has 200 times greater, affinity for Hb. As a result, carboxyhaemoglobin is, formed which causes reduced transport of O2 in body. As, a result, nausea, suffocation and even death occurs., , 4. Assertion (A) pO 2 is the highest in alveoli., , Reason (R) Partial pressure of a gas is the pressure, contributed by individual gas in a mixture., (b) Both A and R are true, but R is not the correct, explanation of A., The pO2 is highest in the alveoli, i.e. 104 mm Hg, because inspiration of oxygen from the atmosphere is by, the lungs. Also pO2 of the blood capillaries around the, alveoli is minimum, thus oxygen diffuse into the blood, capillaries., Partial pressure of a gas is the pressure contributed by, individual gas in a mixture.

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84, , CBSE Term II Biology XI, , 5. Assertion (A) The higher amount of CO 2 can, , diffuse through diffusion membrane per unit, difference in partial pressure as compared to O 2 ., Reason (R) Solubility of CO 2 is 20-25 times higher, than that of O 2 ., (a) Both A and R are true and R is the correct explanation, of A., As the solubility rate of CO2 is 20-25 times higher than, that of O2 the amount of CO2 to diffuse through the, diffusion membrane per unit difference in partial, pressure is much higher when compared to O2., l, , Case Based MCQ, Direction Read the following passage and answer, the questions that follows., The human respiratory system consists of a pair of, lungs and a series of air passages which lead to, lungs. The entire respiratory tract consists of nose,, pharynx, larynx, trachea, bronchi and bronchioles., When air passes through the nose, it is warmed,, moistened and filtered., Hair present in the nose filter out particles in the, incoming air. The air is moistened by the mucus, present in the nose and gets warmed by the blood, that flows through the capillaries., Behind the nose, lies the pharynx with two, passages, one for food and the other for air. The, passage continues from pharynx to larynx and the, opening that leads to larynx is called glottis, it is, covered by epiglottis which prevents food from, entering the passage to lungs. The total surface area, through which gaseous exchange takes place can be, about a hundred times that of the body., (i) Which portion of the human respiratory system is, called the sound box?, (a) Larynx, (c) Nasopharynx, , (b) Trachea, (d) Glottis, , (a) Larynx is a cartilaginous box that aids in sound, production and is referred to as sound box., , (ii) In man, the total number of alveoli is, (a) 300 million, (b) 30,000, (c) 50,000, (d) 7000, (a) There are about 300 million alveoli in both lungs., , (iii) Trachea divides into right and left primary bronchi, of which thoracic vertebra?, (a) 5, (b) 4, (c) 9, (d) 6, (a) Trachea extends upto the midthoracic cavity and, divides at the level of 5th thoracic vertebra into right and, left bronchi which end upto become bronchioles by, repeated divisions., , (iv) Exchange part of the respiratory system comprises, (a) lungs and pleural membrane, (b) alveoli and their ducts, (c) bronchus and their protective covering, (d) diaphragm and alveoli, (b) The respiratory part consists of alveolar sacs and, alveolar ducts., , (v) Identify the correct statement with regard to, human respiratory system., (a) Sternum is present in the dorsal side of the thoracic, chamber, (b) Alveoli are lined by ciliated columnar epithelium, (c) Expiration occurs when there is a positive pressure in, the lungs, (d) Larynx is found in between the epiglottis and trachea, at the anterior side, at the level of 2nd to 4th cervical, vertebrae, (c) Statement in option (c) is correct., Expiration occurs when there is positive pressure in the, lungs whereas inspiration occurs when lungs have, negative pressure.

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85, , CBSE Term II Biology XI, , PART 2, Subjective Questions, l, , Short Answer (SA) Type Questions, 1. Give the name of the organs of respiration in the, , following organisms., (i) Flatworm, (iii) Frog, , (NCERT Exemplar), , system., Diagrammatic view of the human respiratory system is, Epiglottis, , (ii) Birds, (iv) Cockroach, , (i) Body surface, (ii) Lungs, (iii) Skin, buccopharyngeal lining and lungs, (iv) Trachea, , (i) Fishes and Pila, etc., (ii) Insects, centipedes and millipedes, etc., (iii) Certain bacteria, parasitic worms (e.g. Ascaris and, tapeworm), etc., , 3. Complete the following sentences., (i) Nasal chambers are separated from the oral cavity, by ........... ., (ii) A film of .......... lines the alveoli to lower the, surface tension., (iii) Sound is produced by vibration of .......... located, in the .......... ., (iv) Left lung has ..... lobes, while right lung has ........, lobes., (ii) lecithin, (iv) two, three, , 4. What is Adam’s apple? Is it more prominent in, , males or females?’, Larynx is often called as Adam’s apple. It is more, prominent in males than females., , 5. (i) What prevents the trachea and the bronchi from, collapsing?, (ii) Name the epithelium and the cells present in the, walls of trachea, bronchi and bronchioles., (i) Cartilaginous rings are incomplete from behind, which supports the walls of the trachea and the, bronchi to prevent them from collapsing., (ii) Pseudostratified ciliated columnar epithelial tissue, lines the walls of trachea, bronchi and bronchioles, and it is rich in mucus secreting cells., , Larynx, Trachea, Parietal pleura, Bronchus, , Cut end, of rib, , Visceral pleura, Cardiac notch, heart, , 2. Give two examples of each of the following, (i) Animals having internal gills., (ii) Animal groups showing tracheal respiration., (iii) Anaerobes., , (i) palate, (iii) vocal cords, larynx, , 6. Draw a labelled diagram of the human respiratory, , Right lung, Diaphragm, , Pleural membranes, Alveoli, Pleural fluid, Bronchiole, , The human respiratory system, , 7. A person dies in an accident in which his chest, , cavity was punctured, but no lung damage was, there. Point out the cause of death., The movement of air into and out of the lungs is carried, out by creating a pressure gradient between the lungs, and the atmosphere. The pressure within the lungs is less, than the atmospheric pressure so, there is a negative, pressure in the lungs with respect to atmospheric, pressure., The puncture in the chest affects this pressure gradient, maintained by the lungs and thus, may cause cessation of, breathing., , 8. Give the condition of the following muscles during, , expiration., (i) Diaphragm muscles, (ii) Internal intercostal muscles, (i) The muscles of the diaphragm are in a relaxed, position, making it convex., (ii) The internal intercostal muscles are contracting, thus, pulling the ribs downward and inward., , 9. Write the role of diaphragm and intercostal muscles, , in the inspiratory process., The diaphragm and intercostal muscles (external and, internal) present between the ribs help in generation of a, pressure gradient between the lungs and the atmosphere., During inspiration, diaphragm is lowered by contraction, of its muscle fibres and becomes flat. The external, intercostal muscles contract pulling the ribs and sternum, upward and outward.

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86, , CBSE Term II Biology XI, , This increases the volume of thoracic cavity and thus,, decrease the intrapulmonary pressure. The greater, atmospheric pressure outside the body now causes the air, to flow rapidly into external nares, which sequentially, leads to alveoli. Thus, causing inspiration., , 10. In normal breathing, which is the active process, , inspiration or expiration? Explain., In normal breathing, inspiration is an active process as it, is brought about by the contraction of diaphragm and, external intercostal muscles, while expiration is a passive, process as it simply involves relaxation of inspiratory, muscles., , 11. Fill in the blanks., (i) During normal quiet breathing, on an average,, approximately .......... mL of air is inspired or, expired in each breathe, termed as ......... ., (ii) Actually, only about .......... mL of air enters the, lung alveoli for the exchange of gases. The, remaining fills the respiratory passage and is, termed ........ ., (iii) Diaphragm contracts to helps in ...... while the, contraction of abdominal muscles help in ........ ., (iv) Alveolar pO2 is ......... than the venous pO2 in, lungs, while arterial pO2 is ........ than the alveolar, pO2 ., (i), (ii), (iii), (iv), , 14. Complete the missing terms., (i) Inspiratory Capacity (IC) = ...... + ......, (ii) ........... = TV + ERV, (iii) Functional Residual Capacity (FRC) = ....... + ........, (i) Tidal Volume (TV) + Inspiratory Reserve Volume, (IRV)., (ii) Expiratory Capacity (EC)., (iii) Residual Volume (RV) + Expiratory Reserve Volume, (ERV)., , 15. Distinguish between, (i) IRV and ERV, (ii) Vital capacity and Total lung capacity, (i) Distinguishes between IRV and ERV are as follows, IRV, (Inspiratory Reserve, Volume), , ERV, (Expiratory Reserve, Volume), , It is the additional amount, of air that can be inspired, forcibly after a normal, inspiration., , It is the additional amount, of air that can be expired, forcibly after a normal, expiration., , It is about 2500-3000 mL of, air., , It is about 1000-1100 mL, of air., , (ii) Differences between vital capacity and total lung, capacity are as follows, , 500, tidal volume., 350, dead space air, inspiration, forced expiration, higher, lower., , Vital Capacity, , 12. Arrange the following terms based on their volumes, , in an ascending order., (i) Tidal Volume (TV), (ii) Residual Volume (RV), (iii) Inspiratory Reserve Volume (IRV), (iv) Expiratory Capacity (EC), (NCERT Exemplar), Tidal volume → Residual volume →, (500 mL), (1100-1200 mL), Expiratory capacity → IRV, (1500-1600 mL) (2500-3000 mL), , Total Lung Capacity, , It is the maximum volume of It is the total volume of, air a person can breathe in, air present in the lungs, after a forced expiration or, after a forced inspiration., the maximum volume of air a, person can breathe out after a, forced inspiration., It includes TV + IRV +, ERV., , It includes RV + ERV +, TV + IRV., , 16. State the route of foul air from the lungs to outside., , Also state whether TV increases or decreases, during excitement and activity., , 13. Define vital capacity. What is its significance?, (NCERT), , Vital capacity is the maximum amount of air a person can, breathe in after a forced expiration or breathe out after a, forced inspiration. It represents the maximum amount of, air one can renew in the respiratory system during a, single respiration. Thus, the greater the VC, more is the, energy available to the body. Vital capacity shows the, optimum efficiency of lungs in a person. It promotes the, act of supplying fresh air and getting rid of full air,, thereby increasing the gaseous exchange between the, tissues and the environment., , The foul air follows the route given below, Alveoli → Alveolar ducts → Bronchioles → Bronchi →, Trachea → Larynx → Glottis → Pharynx → Internal nares, → Nasal chambers → External nares → Atmosphere., The tidal volume increases 4-10 times during excitement, and activity., , 17. For completion of respiration process, write the, , given steps in sequential manner., (i) Diffusion of gases (O2 and CO2 ) across alveolar, membrane., (ii) Transport of gases by blood., (iii) Utilisation of O2 by the cells for catabolic, reactions and resultant release of CO2 .

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87, , CBSE Term II Biology XI, , (iv) Pulmonary ventilation by which atmospheric air is, drawn in and CO2 rich alveolar air is released out., (v) Diffusion of O2 and CO2 between blood and, tissues., (NCERT Exemplar), Steps in the process of respiration, (i) Diffusion of gases (O2 and CO2) across alveolar, membrane., (ii) Transport of gases by blood to the farthest tissues in, body., (iii) Utilisation of O2 by the cell for catabolic reactions, and resultant release of CO2 and energy., (iv) Pulmonary ventilation by which atmospheric air is, drawn in and CO2 rich alveolar air is released out., (v) Diffusion of O2 and CO2 between blood and tissues., , 18. Why is breathing of women regarded as thoracic,, , while that of male as abdominal? Also state who, among the two has higher vital capacity., In males, the lateral movement of thorax constitutes 25%, of breathing, while the abdominal movement accounts for, 75% breathing. Thus, it is regarded as abdominal, breathing., In women, particularly in pregnant women, the entire, breathing is through lateral movement of thorax. Thus,, breathing in women is regarded as thoracic., The VC is higher in men than in women and in the young, ones than in the old persons., , 19. Diffusion of gases occurs in the alveolar region only, , and not in the other part of respiratory system., Why?, (NCERT), For efficient exchange of gases, respiratory surface must, have certain characteristics such as, (i) it must be thin, moist and permeable to respiratory gases., (ii) it must be large., (iii) it must be highly vascular., Only alveolar region has these characteristics. Thus,, diffusion of gases occurs in this region only., , 20. State the factors that affect the rate of diffusion., Rate of diffusion is affected by the concentration, gradient, membrane permeability, temperature and, pressure. It will take place as long as the difference, between the concentrations of substances across a barrier, are maintained. Membrane permeability also affects the, rate of diffusion. It increases with an increase in, membrane permeability. Changes in temperatue and, pressure also affect the rate of diffusion., , 21. How does haemoglobin help in the transport of, , oxygen from lung to tissues?, Haemoglobin combines with O2 in a reversible manner to, form oxyhaemoglobin., This oxygenated blood circulates in the body. When, it, reaches the tissues having low pO2, the oxygen is, released into the tissues., , 22. State the factors affecting the oxygen-haemoglobin, , binding., Factors that affect the oxygen-haemoglobin binding are, (i) Partial pressure of oxygen, (ii) Partial pressure of carbon dioxide, (iii) Hydrogen ion concentration, (iv) Temperature, , 23. What is the effect of pCO 2 on oxygen transport?, (NCERT), , Increase in pCO2 tension in blood brings rightward shift, of the oxygen-dissociation curve of haemoglobin thereby, decreasing the affinity of Hb for O2. This effect is called, Bohr’s effect., It plays a crucial role in enhancing oxygenation of the, blood in the lungs and in release of O2 in the tissues., , 24. What will be the pO 2 and pCO 2 in the atmospheric, , air compared to those in the alveolar air?, (i) pO2 lesser and pCO2 higher, (ii) pO2 higher and pCO2 lesser, (iii) pO2 higher and pCO2 higher, (iv) pO2 lesser and pCO2 lesser, (i) In the alveolar tissues, where low p O2, high pC O2,, high H + concentration, these conditions are, favourable for dissociation of oxygen from the, oxyhaemoglobin., (ii) When there is high p O2, low pCO2, less H +, concentration and lesser temperature, the factors are, all favourable for formation of oxyhaemoglobin., (iii) When p O2 is high in the alveoli and pCO2 is high in, the tissues then the oxygen diffuses into the blood, and combines with oxygen forming oxyhaemoglobin, and CO2 diffuses out., (iv) When p O2 is low in the alveoli and pCO2 is low in, the tissues then these conditions are favourable for, dissociation of oxygen from the oxyhaemoglobin., , 25. What does the oxygen haemoglobin dissociation, , curve indicate?, The lower part of the curve indicates dissociation of, oxygen from haemoglobin, while the upper part of the, curve indicates acceptance of oxygen by Hb., , 26. What happens to the oxygen dissociation curve in, (i) Alveoli, (ii) Tissues, (i) In the alveoli, the oxygen dissociation curve shifts to, left. It occurs because alveoli has low pCO2, high, pO2, lesser H + concentration and low temperature., (ii) In the tissues, the oxygen dissociation curve shifts to, right. It occurs where there is low pO2, high pCO2,, low pH, high H + concentration and higher, temperature.

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88, , CBSE Term II Biology XI, , 27. How is CO 2 transported in human body., , 33. Why is it not advisable to sleep in closed rooms, , warmed with burning of coals continuously?, , CO2 is transported in the human body in the following, ways, (i) In dissolved form about 7%., (ii) As bicarbonate ions about 70%., (iii) As carbaminohaemoglobin about 20-25%., , A person sleeping in such room gets carbon monoxide, poisoning. CO combines with Hb more readily than, oxygen forming carboxyhaemoglobin. This reduces the, amount of free Hb available for carrying O2. Thus, the, tissue is starved of O2. This is the reason why it is not, advisable to sleep in closed rooms warmed with coals., , 28. What is Hamburger’s phenomenon?, The movement of bicarbonate ions out from the, erythrocytes into the plasma, changes the ionic balance, between plasma and erythrocytes. In order to restore the, ionic balance, the chloride ions diffusion from plasma to, the erythrocytes. This phenomenon is called chloride, shift or Hamburger’s phenomenon., , 34. How marine mammals are able to make long, , underwater dives? Explain., Marine mammals (e.g. seals and whales) can make long, underwater dives as they have, (i) more blood per kg of body weight., (ii) can store more oxygen in blood and muscles., (iii) have a large spleen with blood., (iv) can reduce O2 consumption rate when underwater., , 29. What is the role of carbonic anhydrase in humans?, Nearly 70% of CO2 enters the RBCs and reacts with, water to form carbonic acid in the presence of enzyme,, carbonic anhydrase. This dissociates to form bicarbonate, ions, which are circulated by plasma., , 35. What happens to the respiratory process in a man, , going up a hill?, , At hills, the pressure of air falls and the person cannot get, enough oxygen in the lungs for diffusion in blood. Due to, deficiency of oxygen, the person feels breathlessness, headache, dizziness, nausea, mental fatigue and a bluish, colour on the skin, nails and lips., , 30. Write about Haldane effect. How does Haldane, , effect and Bohr’s effect complement each other?, Haldane effect states that binding of oxygen with, haemoglobin tends to displace CO2 from the blood., It is quantitatively more important in promoting, CO2 transport than the Bohr’s effect in O2 transport., Thus, Haldane effect and Bohr’s effect complement each, other., , 36. Explain chemical control of respiratory rhythm., Large number of chemoreceptors are located in the, carotid bodies (lie bilaterally in the bifurcations of the, common carotid arteries). Their afferent nerve fibres pass, through glossopharyngeal cranial nerve and thus to dorsal, respiratory area of the medulla oblongata, sizeable, number of chemoreceptors are also located in the aortic, bodies (which lie along the arch of aorta)., Their afferent nerve fibres pass through the vagus cranial, nerve and thus, to dorsal respiratory group of neurons., , 31. Differentiate between oxyhaemoglobin and, , carbaminohaemoglobin., Differences between oxyhaemoglobin and, carbaminohaemoglobin are as follows, Oxyhaemoglobin, , Carbaminohaemoglobin, , It is formed by the, combination of oxygen with, the Fe2+ part of, haemoglobin., , It is formed by the, combination of CO2 with, the amino group of, haemoglobin., , Its formation occurs on the, alveolar surface., , Its formation occurs in the, tissues., , 37. Which of the regulatory centre of respiration can, , reduce the inspiratory duration when it is, stimulated?, Respiratory process is regulated by certain specialised, centres present in hindbrain. Amongst them, pneumotaxis, centre is located in the dorsal part of pons Varolii of the, brain, can reduce the duration of inspiration and thus,, alter the respiratory rate., , 32. What makes carbon monoxide more harmful to, , animals than carbon dioxide?, Haemoglobin consists of a protein globin and pigment, haem. The four portions of iron in haem combine with, molecule of oxygen. It is an easy reversible reaction to, form oxyhaemoglobin., Hb + O2 r HbO2, Whereas, the complex formed by the reaction of carbon, monoxide and haemoglobin is incredibly strong, Hb, + CO →, HbCO, (Haemoglobin), , (Carboxyhaemoglobin), , As a result of this strong bonding between the, haemoglobin and carbon monoxide, the haemoglobin, looses its affinity to bind with oxygen thus, may lead to, choking or even death., , (NCERT), , l, , Long Answer (LA) Type Questions, 1. Describe the structure of lungs with suitable, , diagrams., Humans have two lungs one at right and other on left side, in chest region covered by a double-layered pleura with, pleural fluid between them to reduce friction on the lung, surface. These are triangular bags that constitute the, respiratory organ and are site for gaseous exchange, ( O2 / CO2 )., They are situated in the thoracic cavity which is an, anatomically airtight chamber. The thoracic cavity is

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89, , CBSE Term II Biology XI, , enclosed dorsally by thoracic vertebrae, laterally by the, ribs, ventrally by the sternum and closed below by a, dome-shaped diaphragm. The arrangement of lungs is such, that, any change in the volume of thoracic cavity will be, manifested in the pulmonary cavity. This arrangement is, necessary for breathing as the pulmonary volume cannot be, altered directly. The inner membrane of the pleura called, the visceral pleuron, which is firmly bound to the surface, of lungs. The outer membrane, called the parietal pleuron, is held to the thoracic wall and diaphragm by connective, tissue., , From the alveoli, O2 passes into blood of the, capillaries and CO2 diffuses out from blood to, alveoli’s lumen., Air entering lungs, , Ribs and, sternum, raised, , Volume of, thorax, increased, , Epiglottis, Larynx, Trachea, Parietal pleura, Bronchus, heart, , Cut end, of rib, Right lung, , Diaphragm, , Visceral pleura, Cardiac notch, Pleural membranes, Alveoli, Pleural fluid, Bronchiole, , Diagrammatic view of human respiratory system, , (sectional view on the left side), , External Features of Lungs, (i) The left lung has two lobes, i.e. superior lobe and, inferior lobe separated by oblique fissure. It has a, cardiac notch, a concave cavity where the heart lies. It, is longer and narrower than right lung., (ii) The right lung is bigger and has three lobes, i.e., superior lobe, middle lobe and inferior lobe separated, by horizontal fissure and oblique fissure., , 2. Explain the process of inspiration under normal, , conditions., It is an active process by which fresh air enters the lungs. It, can occur if the pressure within the lungs (intrapulmonary, pressure) is less than the atmospheric pressure, i.e. negative, pressure in lungs with respect to atmospheric pressure., Following muscles play an important role, (a) Diaphragm It is lowered by the contraction of its, muscle fibres and becomes flat. This causes an increase, in the volume of thoracic chamber in the, antero-posterior axis., (b) External Intercostal Muscles They occur between, the ribs (internal intercostal muscles are related to, expiration). The external intercostal muscles contract, and pull the ribs and the sternum upward and outward, thus, increasing the volume of thoracic chamber in, dorsoventral axis., Thus, the overall increase in the volume of thoracic, cavity causes an increase in pulmonary volume. As a, result, there is a decrease in the intrapulmonary, pressure. The greater atmospheric pressure outside the, body now causes air to flow rapidly into external nares,, which sequentially leads to alveoli., , Lungs expanded, , Rib cage, Diaphragm, contracted, , Mechanism of breathing showing inspiration, , 3. Explain the mechanism of expiration in humans., , Also, give diagram of this process of breathing., Expiration is a passive process by which CO2 is, expelled out from the lungs. It takes place when the, intrapulmonary pressure is higher than the atmospheric, pressure., The movements of muscles involved in the breathing, mechanism are as follows, (i) Diaphragm The muscle fibres of the diaphragm, relax making it convex, decreasing volume of the, thoracic cavity., (ii) Internal Intercostal Muscles These muscles, contract thus, pulling the ribs downward and, inward, decreasing the thoracic volume., The overall volume of the thoracic cavity thus,, decreases thereby reducing the pulmonary, volume., As a result, the intrapulmonary pressure increases, slightly above the atmospheric pressure. This in, turn causes the expulsion of the air from the lungs., The process of expiration is simpler than, inspiration., Air expelled from lungs, Volume of, thorax, decreased, , Ribs and sternum, returned to original, position, (lowered), , Lungs return, to original, position, Diaphragm, relaxed, and arched, upwards, , Mechanism of breathing showing expiration

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90, , CBSE Term II Biology XI, , 4. Explain the different respiratory volumes and, , capacities., The different volumes and capacities are as follows, (i) Tidal Volume (TV) It is the volume of air inspired or, expired during normal breathing in relaxed or, resting position. It is about 500 mL. A healthy man, can inspire or expire approximately 6000-8000 mL of, air per minute., (ii) Inspiratory Reserve Volume (IRV) It is the, additional amount of air that can be inspired forcibly, after a normal inspiration. It is about 2500-3000 mL, of air., (iii) Expiratory Reserve Volume (ERV) It is the, additional volume of air that can be expired forcibly, after a normal expiration. It is about 1000-1100 mL., (iv) Residual Volume (RV) It is the volume of air, remaining in the lungs even after a forcible, expiration. It is about 1100-1200 mL. It cannot be, measured by spirometry., Various pulmonary capacities are derived from the above, mentioned volumes. These are as follows, (i) Inspiratory Capacity (IC) It is the total volume of, air a person can inspire after a normal expiration. It, is about 2500-3000 mL. It includes, IC = TV + IRV, (ii) Expiratory Capacity (EC) It is the total volume of, air a person can expire after a normal inspiration. It, includes, EC = TV + ERV, (iii) Functional Residual Capacity (FRC) It is the, volume of air that will remain in the lungs after a, normal expiration. It includes, FRC = RV + ERV, (iv) Vital Capacity (VC) It is the maximum volume of air, a person can breathe in after a forced expiration or, the maximum volume of air a person can breathe out, after a forced inspiration., This includes, TV + IRV + ERV ., (v) Total Lung Capacity It is the total volume of air, present in the lungs after a forced (maximum), inspiration. It includes, RV + ERV + TV + IRV or (VC+RV), , (i) Exchange of gases between alveoli and blood, (external respiration)., (ii) Exchange of gases between blood and tissue cells, (internal respiration)., The exchange of gas between tissue blood capillaries and, tissue cells is called internal respiration. pO2 in, oxygenated blood is more than that in body cells and, pCO2 in oxygenated blood is less than that in body cells., Due to the partial pressure differences created, oxygen, diffuses from capillary blood to body cells and CO2, diffuses from body cells to the capillary blood. The, deoxygenated blood formed is carried to the heart by, veins and finally to lungs for purification., The diagram below represents gaseous exchange at the, alveolus and body tissues, Inspired air Expired air, Alveolar air, , Blood entering, pO2=104mmHg, alveolar capillaries pCO =40mmHg, 2, CO2 O2, Pulmonary, artery, , Systemic veins, (carrying, deoxygenated, blood), pO2 =40 mmHg, pCO2=45 mmHg, , Alveolus, Blood entering, alveolar capillaries, , CO2 O2, Pulmonary vein, , Systemic arteries, (carrying oxygenated blood), pO2 =95 mmHg, pCO2=40 mmHg, , CO2 O2, CO2 O2, , Body tissues, Diagrammatic representation of exchange of gases at the alveolus, and the body tissues with blood and transport of oxygen and carbon, dioxide, , 6. What is tidal volume? Find out the tidal volume for, , a healthy human in an hour time?, Also, label the parts A, B, C and D in the given, figure of alveolus., , D, , 5. Give diagrammatic representation of exchange of, , gases at the alveolus and the body tissues with, transport of O 2 and CO 2 . Also, explain how does, exchange of gases occur between blood and tissue, cells., Primary sites for gaseous exchange are the alveoli and, tissues. Gaseous exchange occurs by simple diffusion, based on concentration gradient. It occurs in two ways, , C, A, B, , Tidal volume is the volume of air inspired or expired, during normal breathing in relaxed or resting position. Its, volume is about 500 mL.

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91, , CBSE Term II Biology XI, , Amount of Tidal Volume (TV) in an hour, = Respiratory rate × TV × 60 min, = (12 − 16 breaths per minute) × 500 mL × 60, = 16 × 500 × 60 = 480000 mL, TV = 360 − 480 L, , Therefore, the hourly tidal volume for healthy human is, approximately 3. 6 × 10 5 mL to 4. 8 × 10 −5 mL., In figure parts labelled as, A — Alveolar cavity,, B — Alveolar wall,, C — Red blood cells,, D — Basement substance., , 7. What are the major transport mechanisms for, , CO 2 ? Explain., , (NCERT), , CO2 diffuses out of the cells into capillaries. Major, transport mechanisms for CO2 are, (i) Transport in Dissolved Form About 7% CO2 is, carried in a dissolved state through plasma due to, high solubility., (ii) Transport as Bicarbonate The largest fraction (about, 70%) is carried in plasma as bicarbonate ions (HCO−3 )., At the tissues site, where pCO2 is high due to, catabolism, CO2 diffuses into the blood (RBCs and, plasma) and forms HCO–3 and H + ., Carbonic, , CO2 + H 2O, (Carbon, dioxide), , r, , +, , H+, (Hydrogen, ion), , This reaction is faster in RBCs because they contain, an enzyme carbonic anhydrase. Hydrogen ion, released during the reaction bind to Hb, triggering, the Bohr effect., At the alveolar site, where pCO2 is low, the reaction, proceeds in opposite direction forming CO2 and, H 2O. Thus, CO2 trapped as bicarbonate at tissue, level and transported to alveoli is released as CO2., (iii) Transport as Carbaminohaemoglobin Nearly, 20-25% CO2 is carried by haemoglobin as, carbamino-haemoglobin. CO2 entering the blood, combines with the NH 2 group of the reduced Hb., HbO2 + CO2, HbCO2, + H + + O2, , r, , 9. Give cause, symptoms and preventions of the, , following disorders., (i) Asthma, (ii ) Emphysema, (iii) Occupational respiratory disorder, , -, , H 2CO3, anhydrase (Carbonic, acid), Carbonic, , HCO−3, anhydrase (Bicarbonate, ion), , It is under dual control, i.e. nervous and chemical. This is, explained below as, i. Neural Control, The respiratory rhythm centre is composed of a group of, neurons located in the medulla oblongata and pons, Varolii., Pons Respiratory Centres, Neural signal from pneumotaxic centres stimulated, reduce the duration of inspiration, altering the respiratory, rate., A chemosensitive area is located adjacent to rhythm, centre that is highly sensitive to CO2 and hydrogen ions., They increase activity of this centre, which in turn signals, the respiratory centre to make necessary changes in order, to eliminate these substances. Oxygen does not have a, significantly direct effect on the respiratory centre of the, brain in controlling respiration., ii. Chemical Control, Large number of chemoreceptors are located in the, carotid bodies, which lie bilaterally in the bifurcations of, the common carotid arteries. Their afferent nerve fibres, pass through glossopharyngeal cranial nerve and thus, to, dorsal respiratory area of the medulla oblongata., Receptors of aortic arch and carotid artery recognise, change in CO2 and H + concentration and send necessary, signals to the rhythm centre for remedial actions., , (Carbaminohaemoglobin), , 8. Explain the process of regulation of respiration., The respiratory rhythm can be maintained and moderated, by human beings to suit the demands of the body tissues., , The cause, symptoms and preventions of the disorders, are as follows, (i) Asthma (difficulty in breathing), Causes Allergens stimulate the release of histamine, from the mast cells causing inflammation of bronchi, and bronchioles., Symptoms Coughing, wheezing, excess amount of, mucus clog the bronchi and bronchioles., Preventions By avoiding exposure to allergens., (ii) Emphysema (inflation or distension of bronchioles, or alveolar sacs), Causes Cigarette smoking and inhalation of other, smoke or toxic substances over a period of time leads, to damage of alveolar walls., Symptoms Due to collapse of alveolar septa, surface, area for gas exchange is reduced, lungs inflated,, exhalation becomes difficult., Preventions Cigarette smoking and exposure to air, pollutants must be avoided.

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92, , CBSE Term II Biology XI, , (iii) Occupational Respiratory Disorders, (it is due to occupation of individual especially those in, grinding or stone breaking industry), Causes Occur due to chronic exposure of harmful, substances as silica, aesbestos, etc., (silicosis,, asbestosis). The defence mechanism of body fails to, cope with the situation., Symptoms Proliferation of fibrous connective tissue, (fibrosis) of upper part of lung causing inflammation., Preventions Minimise use of harmful dust. Use of, protective gears and clothing at work place. Regular, health check up of workers., l, , Case Based Questions, 1. Observe the diagram given below and answer the, questions that follows., To pulmonary vein, Air, Alveolar wall, (one-celled thick), From, pulmonary, artery, Blood, capillary, , A, Alveolar cavity, , Red blood cells, O2 enters blood, CO2 enters alveolus, , (i) What is being represented in the above diagram?, The above diagram represents a section of an alveolus with, pulmonary capillary, showing gaseous exchange., , (ii) Which vein contains the oxygenated blood in, humans?, Pulmonary vein is the only vein in the body that carries, oxygenated blood, from the lungs to the left auricle and, thereafter, it gets distributed to all parts of the body., , (iii) How is oxygen carried from alveoli into the blood in, pulmonary capillaries?, Movement of oxygen from alveoli into the blood in, pulmonary capillaries occurs by the process of simple, diffusion., , (iv) Which factors affect the rate of diffusion?, Concentration/.pressure gradient, solubility of gases and the, thickness of the membrane(s) involved in diffusion are some, important factors which affect the rate of diffusion., , (v) Identify A and write its feature and/or function., A is basement substance forming alveolar capillary, membrane that allows gaseous exchange between blood, and alveolar air., , 2. Direction Read the following passage and answer, the questions that follows., Respiratory diseases are highly complex, being, driven by host-environment interactions and, manifested by structural, functional and, inflammatory abnormalities which vary as per, time and conditions. It is possible to study the, collective behaviour of their symptoms in order to, find appropriate measures to deal with them., Asthma is one such disorder characterised by, recurrent attacks of breathlessness and wheezing, that varies from person to person in terms of, severity and frequency symptoms of asthma, include inability to breathe, coughing fits,, wheezing fits. It is a condition with no known, cures, but an effective management., Occupational respiratory disease is any lung, condition that one gets at work. It occurs due to, repeated exposure to certain toxins., Symptoms of ORD can vary. They depend on, your work setting, type of disease and state of, health., (i) Name the chronic respiratory disorder caused, mainly by cigarette smoking., Emphysema is a destructure disease of the lungs in, which alveoli get destroyed. The primary cause of, emphysema is smoking as the toxins present in the, cigarette damage the alveoli., , (ii) What step can be taken as a preventure measure, to cure emphysema?, Emphysema is mainly caused due to cigarette smoking, hence, avoiding cigarettes can be a preventive measure, to cure emphysema., , (iii) How can asthma be effectively managed? ., Asthma can be effectively managed with the help of, inhalers which open the swollen airways that block, breathing. Also, medications are helpful in managing, asthmatic conditions.

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93, , CBSE Term II Biology XI, , (iv) Give example of an occupational respiration disorder?, Occupational respiratory disorders arise due to repeated or, prolong exposure to certain toxins at work places, e.g. silicosis., , (v) How can occupational respiratory disorders be, prevented?, Occupational respiratory disorders can be prevented by, avoiding areas with increased levels of dust and smoke,, wearing protective masks and consuming antihistamine tablets, daily., , 3. Observe the diagram given below and answer the, questions that follows., Air entering lungs, , Ribs and, sternum, , Volume of, thorax, , Lungs, , Rib cage, Diaphragm, , (i) What happens to the diaphragm during the, process shown above?, During inspiration (depicted above), the diaphragm, contracts, putting backwards by the partial, flattening., , (ii) In which respiratory volume, air inhaled and, exhaled without any force?, The volume of air breathed in and out without any, force in each breath is called Tidal Volume. It is, about 500 mL or 0.5 L., , (iii) What is the causes of decreased, intrapulmonary pressure during inspiration?, Inspiration is initiated by the contraction of, diaphragm. It is achieved by the contraction of the, external intercostal muscles which up lift the ribs, and the sternum. The overall increase in the, thoracic volume causes a similar increase in the, pulmonary volume. This decreases the, intrapulmonary pressure forcing the air from outside, to move into the lungs (i.e. inspiration)., , (iv) How is negative pressure breathing helpful for, mammals?, If allows the mammals to eat and breathe at the, same time.

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Chapter Test, Multiple Choice Questions, , Assertion-Reasoning MCQs, , 1. Correct sequence of the air passage in humans is, (a), (b), (c), (d), , Nose → Larynx → Pharynx → Bronchioles → Alveoli, Nose → Pharynx → Larynx → Bronchioles → Bronchi, Nose → Pharynx → Larynx → Bronchioles → Trachea, External nostril → Nasal passage → Internal nostril → Pharynx →, Larynx → Trachea → Bronchi → Bronchiole → Alveoli, , 2. Lungs do not collapse between breaths and some air always, remains in the lungs which can never be expelled because, (a) there is negative pressure in the lungs, (b) there is negative intrapleural pressure pulling at the lung walls, (c) there is positive intrapleural pressure, (d) pressure in the lungs is higher than the atmospheric pressure, , 3. Identify A , B and C in the given diagram and choose the, , Direction (Q. Nos. 1-3) Each of these questions, contains two statements, Assertion (A) and Reason, (R). Each of these questions also has four alternative, choices, any one of which is the correct answer. You, have to select one of the codes (a), (b), (c) and (d), given below., (a) Both A and R are true and R is the correct, explanation of A, (b) Both A and R are true, but R is not the correct, explanation of A, (c) A is true, but R is false, (d) A is false, but R is true, , 1. Assertion (A) Most fishes when out of water, die, of suffocation., , correct option accordingly., , Reason (R) Atmospheric air contains less oxygen, content than oxygen dissolved in water., , Air, , 2. Assertion (A) CO2 transport occurs very fast, Alveolar wall, (one-celled thick), , C, , through RBCs., Reason (R) Enzyme carbonic anhydrase is absent, in the blood plasma., , A, , 3. Assertion (A) Blood oxygen does not have, significant effect on the respiratory centre of, brain., B, , Blood, capillary, , (a), (b), (c ), (d), , A–Alveolar cavity, B–WBC, C–Capillary wall, A–Alveolar cavity, B–RBC, C–Systemic wall, A–Alveolar cavity, B–RBC, C–Basement membrane, A–Alveolar cavity, B–WBC, C–Systemic wall, , 4. Blood does not become acidic although it carries CO2, because, (a), (b), (c), (d), , CO 2 is continuously diffused through tissues, CO 2 combines with H 2O to form H 2CO3, in CO 2 transport, buffer plays an important role, CO 2 is absorbed by WBC, , 5. Which one of the following options correctly represents the, lung conditions in asthma and emphysema, respectively?, (a), (b), (c), (d), , Increased respiratory surface; Inflammation of bronchioles, Increased number of bronchioles; Increased respiratory surface, Inflammation of bronchioles; Decreased respiratory surface, Decreased respiratory surface; Inflammation of bronchioles, , Reason (R) Increased pCO2 and H+ levels, detected by chemoreceptors activate the, respiratory centres to mediate the necessary, adjustments., , Short Answer Type Questions, , 1. Write note on larynx., 2. What is meant by inspiration and expiration?, 3. Name the factors that affect the rate of diffusion, of gases in the lungs., , 4. What happens to oxyhaemoglobin, when the, blood reaches the tissues?, , 5. Draw a labelled diagram of a section of an, alveolus with a pulmonary capillary., , Long Answer Type Questions, , 1. Explain human respiratory system., 2. How are gases (O2 and CO2 ) transported in, blood?, , Answers, Multiple Choice Questions, 1. (d), , 2. (b), , 3. (c), , 4. (c), , Assertion-Reasoning MCQs, 1. (c), , 2. (c), , 3. (a), , 5. (c), , For Detailed Solutions, Scan the code

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95, , CBSE Term II Biology XI, , CHAPTER 06, , Body Fluids, and Circulation, In this Chapter..., , l, , l, , l, , l, , Human Circulatory System, , l, , Blood, , l, , Double Circulation, , l, , Lymph, , l, , Regulation of Cardiac Activity, , l, , Circulatory Pathways, , l, , Disorders of Circulatory system, , During metabolism, cell produces some useful and some, waste products. Substances that are useful, need to be, transported to other cells, while harmful or waste, substances are to be removed from the body., Thus, circulatory system is formed with the carrier, a fluid, medium that circulates throughout the body and fulfils the, need of the body cells for the distribution of useful, products and elimination of waste products., Simple organisms such as sponges and coelenterates have, simple body organisation. These are in direct contact with, atmosphere. Thus, they do not require any circulatory, system. They instead circulate water from their, surroundings into their body cavities. This facilitates the, cells to exchange gases and excretory substances with, immediate surroundings., In more complex organisms, special fluids are used to, transport these substances within the body. Blood and, lymph are the two types of fluids that act as a carrier in the, body., , Blood, l, , l, , It is a special connective tissue comprising of a fluid, matrix, plasma and formed elements. Plasma forms the, fluid medium in which the blood cells (corpuscles) float, and carry out different important functions., , I. Plasma, l, , l, , l, , l, , l, , It is a straw coloured, viscous, slightly alkaline aqueous, body fluid. It forms about 55% of the blood., It is composed of many organic and inorganic substances., It contains 90-92% water and 6-8% solutes in it., The solutes found in plasma are various ions (like Na + ,, Mg 2+ , Ca 2+ , HCO –3 , etc.), glucose, traces of other sugars,, plasma proteins, amino acids, hormones, cholesterol, other, lipids, urea, other wastes and other organic acids., Factors for clotting or coagulation of blood are also present, actively in the plasma. Plasma without the blood clotting, factors is called serum., Proteins found in plasma are important as they are, responsible for providing viscosity to the plasma. The, major proteins found in plasma are fibrinogen, globulins, and albumins., , Functions of Plasma, It performs various functions in the blood, these are as, follows, (i) Helps in transport and uniform distribution of heat all, over the body., (ii) Provides body immunity., (iii) Maintenance of blood pH.

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96, , CBSE Term II Biology XI, , (iv) Helps in prevention of blood loss., (v) Fibrinogen helps in blood clotting, globulin helps in, defence mechanism, albumin maintains osmotic, balance., , (b) Eosinophils They are characterised by their bilobed, nucleus. They are stained bright red in colour with, acidic dye (due to the presence of numerous coarse, granules in it) such as eosin., They are about 2-3% of total WBCs. They resist, infections and are also associated with all allergic, reactions. They also help in dissolving blood clot. They, help to destroy the toxic substances present in the, body., During allergic conditions, the number of eosinophils, increases in the body., (c) Basophils They contain fewer coarse granules than the, eosinophils and can be stained with basic dyes such as,, methylene blue. They are found least abundantly, (0.5-1.0%) among WBCs. They secrete histamine,, serotonin, heparin, etc., and are involved in, inflammatory reactions., , II. Formed Elements, The formed elements or blood corpuscles include, erythrocytes, leucocytes and platelets. These constitute about, 45% of the blood., , 1. Erythrocytes (Red Blood Corpuscles), l, , l, , l, , l, , l, , These are the most abundant of all cells found in the blood., They are red in colour due to the presence of a pigment, called haemoglobin, which acts as an oxygen carrier. The, formation of RBCs takes place in the red bone marrow in, adults., RBCs are biconcave, disc-shaped cells with the diameter of, about 7-8 micron. The shape of RBC is slightly variable. As, there are no cell organelles found in it, whole volume is, filled with haemoglobin. A healthy individual has about, 12-16 gm of haemoglobin in every 100 mL of blood., In men, the average number of RBC is about 5-5.5 million, per cubic millimeter (mm 3 ) of blood., In women, the average number is about 4-4.5 mm 3 of, blood., Total lifespan of RBC is 120 days. After which RBC, becomes non-functional and gets destroyed in spleen., So, spleen is graveyard of RBCs., , 2. Leucocytes (White Blood Cells), l, , l, , l, , These are known to be the most active and motile, constituent of blood as well as lymph. They do not possess, the red colour pigment (haemoglobin) in them, so they are, colourless in nature., These are nucleated and are generally short lived cells., The number of WBCs are relatively lesser in number,, about 6000-8000 mm 3 of blood. They move in an, amoeboid fashion. These can squeeze through capillary, wall and move to the site of action. This phenomenon is, called diapedesis., Leucocytes or white blood corpuscles are categorised into, two main categories such as, , ii. Agranulocytes, They lack granules in their cytoplasm and have rounded or, oval nucleus. Agranulocytes are also further subdivided into, two main types, (a) Lymphocytes These are smaller in size and have, rounded nucleus. Lymphocytes are of further two, types, i.e. B-cells and T-cells. Both of these (i.e. B and, T-cells) are responsible for immune responses of the, body., (b) Monocytes These are largest of all types of WBCs, but, are fewer in number. Mature monocytes are known as, macrophages. They help to kill foreign particles. These, are phagocytic in nature., , RBC, , Neutrophil, , Eosinophil, , Basophil, , T-lymphocyte, , Monocyte, Diagrammatic representation of, formed elements in blood, , B-lymphocyte, , 3. Blood Platelets (Thrombocytes), l, , i. Granulocytes, They contain granules in the cytoplasm and have regularly, lobed nucleus. The granulocytes are further subdivided into, three main types, (a) Neutrophils These are the most abundant cells, (about 60-65%) of the total WBCs. They stain equally, well with acidic as well as basic dyes, because they are, neutral in nature. These are phagocytic cells that, destroy foreign organisms entering the body., , Platelets, , l, , l, , These are cell fragments produced from megakaryocytes, (i.e. the special cells found in the red bone marrow)., These are oval-shaped, disc-like cells found only in, mammalian blood. These are devoid of nuclei., Platelets contain mitochondria, Golgi bodies and some, other structures such as granules, tubules, filaments of, actin and myosin, ADP, etc., Blood normally contains 150000-350000 platelets per cubic, meter (mm 3 ). A reduction in their number can lead to

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97, , CBSE Term II Biology XI, , l, , l, , clotting disorders which will lead to excessive blood loss, from the body if some one get injured., The lifespan of platelets is only about 7-12 days. The, formation of thrombocytes is called thrombopoiesis., Function of Blood Platelets Their main function in the, body is to release factors most of which are involved in, coagulation or clotting of blood., , Blood Groups, l, , Two methods of blood grouping include ABO system (first, reported by Karl Landsteiner) and Rh-system., , 1. ABO Grouping, Red blood cells of different people differ due to the, presence or absence of two surface antigens (A and B), which are responsible for different types of blood groups,, i.e. A, B, AB and O., AB blood group is universal acceptor and O blood group is, universal donor., Different blood groups and their donor compatibility are, listed below, l, , l, , Natural Anticoagulants, Inside an intact blood vessel, the blood does not coagulate, because of the presence of an active anticoagulants, i.e., heparin or antiprothrombins. These procoagulants are, present in the blood in their inactive forms., Haemophilia is a genetic disease, which is caused due to, deficiency of prothrombin, fibrinogen and vitamin-K. In this, condition, the blood does not clot. If there is any injury in, such person, death of that person occurs due to excessive, bleeding., Formation of a Clot, l, , l, , l, , Blood, groups, , Antigen on, RBCs, , Antibodies in, plasma, , Donor’s, group, , A, , A, , Anti-B, , A, O, , B, , B, , Anti-A, , B, O, , AB, , A, B, , Nil, , AB, A, B, O, , O, , Nil, , Anti-A, B, , O, , Clotting of blood is a complex process that involves various, enzymatically controlled steps for its completion., , l, , An injury or trauma causes stimulation of platelets cells to, release certain platelet factors. This in turn activates the, mechanism of coagulation or clotting of blood at the site of, injury., It occurs in following three steps, (i) Thromboplastin, helps in formation of an enzyme, prothrombinase (which inactivates heparin) that, converts the inactive plasma protein, i.e. prothrombin, into its active form thrombin., (ii) Thrombin thus, acts as a proteolytic enzyme to convert, fibrinogen molecule (produced from the liver in the, presence of vitamin-K) to form insoluble fibrin, monomer., Blood platelets, , Injured tissue, , Disintegrate, , Releases, , 2. Rh Grouping, l, , l, , l, , l, , In some individuals, Rh antigen is present similar to one, present in Rhesus monkeys. Such individuals are called Rh, positive (Rh + ), while person lacking Rh-factor are called, Rh negative (Rh − )., Rh-factor is needed to be checked before blood transfusion., A well known example of Rh-incompatibility is seen in, case of Rh − mother pregnant with its Rh + foetus., During pregnancy, Rh antibodies from Rh − mother pass to, Rh + foetus and destroy foetal RBC. This condition is, known as erythroblastosis foetalis. The foetus suffers from, severe anaemia and jaundice., First pregnancy is quite safe in this case however, in, subsequent pregnancies, anti-Rh antibodies are, administered to the mother immediately after the delivery of, first child., , Coagulation of Blood, l, , When an injury is caused, the wound normally does not, continue to bleed for a long time and the blood stops, flowing after some time. It is the natural property exhibited, by the blood to check the excessive loss of blood from an, injury or trauma., , Thromboplastin, Ca2+ proteins, , Platelet factor-3, (=platelet thromboplastin), , Ca2+ proteins, Prothrombinase, , Step I, , Inactivates heparin, and catalyses, , Step II, Step III, , Prothrombin, , Ca2+, , Fibrinogen, (Fibrin + Blood cells), , Thrombin, catalyses, Fibrin, Clot, , Role of thrombocytes in blood coagulation, , This reaction required thrombokinase an enzyme, complex, which is formed by a series of linked, enzymatic reactions (with cascade effects) which, involves a number of various factors present in the, plasma in their inactive state., Both the changes mentioned above require Ca 2+ ions, for their reaction., (iii) These fibrin monomers polymerise to long, sticky, fibres. The fibrin threads forms a fine network of, threads called fibrins, in which dead and damaged, formed elements of blood are trapped., This finally leads to the formation of a clot or coagulum,, which is a dark reddish brown scum formed over the, surface of injury.

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98, Functions of Blood, Blood performs the following important functions, (i) Helps in transportation of respiratory gases (i.e. O 2 ,, CO 2 , etc)., (ii) Helps in healing of wounds., (iii) Maintains body pH, water and ionic balance., (iv) Fight against infections by forming body immunity., (v) Also helps in transportation of hormones from, endocrine glands to target organs., (vi) Coagulation of blood., (vii) Helps in transportation of body wastes from different, body parts to kidneys., (viii) Maintains normal body temperature., , Lymph (Tissue Fluid), l, , l, , l, , It is another fluid connective tissue that floats inside, specialised vessels known as lymph vessels., It is a colourless fluid containing high concentration of, WBCs (specialised lymphocytes). The overall composition, of lymph is similar to blood with the exception of absence, of RBCs, platelets and some plasma proteins and in having, less calcium and phosphorous than their levels in the, blood. It also contains all the ions, present in the blood, plasma., It is an elaborate network of vessels, which collects the, interstitial fluid (tissue fluid), along with some protein, molecules drains it back into the major veins. The, lymphatic vessels are present in all tissues (except the, central nervous system and cornea)., , Functions of Lymph, Lymph performs the following important functions, (i) It acts as an important carrier of nutrients, hormones, etc., (ii) Absorption of fat also occurs through lymph in the, lacteals present in the intestinal villi., (iii) Also helps in the renewal of ECF., (iv) Maturation of lymphocytes, i.e. B-cells and T-cells, occur with the help of lymph nodes, releasing them into, the lymph., , Human Circulatory System, Blood vascular system of human consists of a muscular, chambered heart, a network of closed branching blood, vessels and blood, (i.e. the fluid which is circulated)., , Heart, It is a mesodermally derived organ, situated in the thoracic, cavity in between the two lungs. It appears to be slightly, tilted towards the left side. It is a hollow, fibromuscular, organ, slightly conical in shape of about 12 cm length and, , CBSE Term II Biology XI, , 9 cm breadth. The upper broad part is called the base and the, lower narrow part known as the apex. It has a size of a, clenched fist., , Protective Covering, The heart is protected by a double-walled membranous sac or, a bag called pericardium. The fluid present between two, membrane is called pericardial fluid. This fluid helps in, keeping the surface of the heart moist and also protects it, from shock and mechanical injuries., Structure of human heart can be studied under two heads for, easy understanding, i.e. external and internal structure., , External Structure, Externally, the human heart is composed of four chambers,, i.e. two relatively small upper chambers called auricles (sing., atria) and two larger lower chambers called ventricles., The right atrium is slightly larger than the left atrium. Both, these atria are meant to receive blood from different body, parts., , Internal Structure, Internally, the chambers of heart, i.e. two auricles (atria) and, ventricles are separated by different septa and valves., , Auricles (Atria), These are the upper two thin-walled and smaller chambers., They serve to receive the blood, therefore are called, receiving chambers (right atrium and left atrium). Both the, right and the left atria are separated by a thin, muscular wall, known as interatrial septum., (a) Right Atrium This right chamber deals with only, impure (deoxygenated) blood. It receives impure blood, from various parts of the body, through two major, veins, i.e. superior and inferior vena cava., It also receives blood from the walls of the heart itself, (through a coronary sinus)., (b) Left Atrium This chamber is meant to deal with only, pure (oxygenated) blood. It receives blood (pure) from, lungs through two pulmonary veins (i.e. one from the, each lung)., Ventricles, These are lower two chambers of the heart, that pumps the, blood away from the heart. This functions as pumping, chambers. Both the right and the left ventricles are separated, by the interventricular septum., The atrium and the ventricle of the same side are also, separated by another septum, a thick fibrous tissue called, Atrioventricular septum (i.e. AV septum)., (a) Right Ventricle It receives impure blood from right, atrium and pumps blood into pulmonary artery, which, further takes this blood to lungs for purification., (b) Left Ventricle It receives pure (oxygenated) blood, from left atrium and pumps its pure blood to aorta

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99, , CBSE Term II Biology XI, , (largest artery in the pathway), which in turn takes this, blood to whole body and organs., , Left atrium, , The signals which arise from SA node become weak when, they reach ventricles because ventricles are far away from SA, node. Thus, to strengthen these signals, another mass of, tissue is seen in the lower left corner of the right atrium close, to the atrioventricular septum (i.e. at the junction of, ventricles and atrium) known as AV node. This is also known, as pacesetter., , Bundle of His, , 3. Bundle of His, , Left ventricle, , A bundle of nodal fibres, i.e. Atrioventricular bundle (AV, bundle) continues from the AV node, which passes through, the atrioventricular septa to emerge on the top of the, interventricular septum immediately dividing into a right and, left bundle., This bundle gives rise to a network of minute fibres, (which are myocardial in origin) throughout the ventricular, musculature of the respective side known as Purkinje fibres., These fibres along with the right and left bundles are called, bundle of his. The Purkinje fibres conduct impulses to all, portions of ventricular walls of the heart., , Aorta, Vena cava, , Pulmonary artery, , Sinoatrial node, Right atrium, Atrioventricular, node, Chordae tendinae, , Interventricular septum, , Right ventricle, , 2. The Atrioventricular Node or AV Node (AVN), , Apex, , Section of a human heart, , Cardiac Valves, Apart from septum, heart is also separated by the various, valves. These valves act as a door-like structure in the heart, that serves to maintain the unidirectional flow of blood., Different valves present in the heart are given below, (i) Tricuspid Valve It is formed by three muscular flaps, or cusps to guard the opening between the right atrium, and the right ventricle., (ii) Bicuspid Valve (Mitral valve) It is the type of valve that, guards the opening between the left atrium and the left, ventricle., (iii) Semilunar Valve The opening of the right and the left, ventricles into the pulmonary artery and the aorta,, respectively are provided with the semilunar valves., Functions of Cardiac Valves, The valves in the heart allow the flow of blood only in one, direction, i.e. from the atria to ventricles and from the, ventricles to the pulmonary artery or aorta and prevent any, backward flow of blood into four chambers., , Conducting System of Heart, The heart is made up of cardiac muscles. The ventricular, walls are thicker than that of the atrial walls. The rhythm of, heart is maintained by a highly specialised cardiac, musculature called the nodal tissue distributed evenly in the, heart muscles., 1. The Sinoatrial Node or SA Node (SAN), SA node is a small flattened patch of specialised tissue, present in the right upper corner of the right atrium., The impulse generated by this node spreads in all directions, of the heart (i.e. go to both auricles and causes their, relaxation and contraction)., , Working of Nodal Tissue, l, , l, , The nodal musculature possesses the ability of generating, action potentials without any external stimuli, i.e. it is, autoexcitable. However, the nodal system generates, different number of action potential at different parts in a, minute. The SAN can generate the maximum number of, action potentials, i.e. 70-75 min −1 ., It is also responsible for the initiation and maintenance of, the rhythmic contractile activity of the heart. Therefore,, the SAN (i.e. SA Node) is also called pacemaker. Our heart, normally beats 70-75 times in a minute (i.e. average, 72 beats/min)., , Blood Vessels, As man has a closed circulatory system, the blood strictly, flows in a fixed route through arteries and veins maintains a, continuous flow throughout the body inside the closed tubes, or blood vessels., These tubes or vessels are of mainly two types, , Arteries, These blood vessels carry blood from the heart to different, body parts. All arteries carry pure or oxygenated blood, with, the exception of pulmonary artery that carries the impure or, deoxygenated blood (i.e. from heart to the lungs for, purification). As the walls of arteries are thick and, non-collapsible, the pressure inside them is very high.

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100, Features of Arteries, (i) Valves are absent in arteries., (ii) Arteries are divided into fine branches, known as, arterioles, which are further divided to form finer, branches, called capillaries., , CBSE Term II Biology XI, , Ventricular Systole, l, , l, , Veins, These are another type of blood vessels that bring blood, from different body parts to the heart, i.e. carry blood, towards the heart. All veins are meant to carry impure blood, except the pulmonary vein that carries pure blood, i.e. from, lungs to the heart. Veins are provided with valves to prevent, backward flow of blood., , l, , Cardiac Cycle, l, , l, , l, , l, , l, , The heart pumps the blood to all parts of the body. The, changes that take place in heart during one heartbeat,, together constitute cardiac cycle., The heartbeats at an average rate of about 72 times/min., Thus, the total duration of a cardiac cycle is 0.8 s. During, a heartbeat, the contraction and relaxation of atria and, ventricles take place., The phase of contraction is known as systole, while the, relaxation phase is called the diastole. Thus, a single, heartbeat consists of a systole and diastole of both the atria, and the ventricles., To begin with the cardiac cycle, all four chambers of heart, are in a relaxed state, i.e. they are in joint diastole, during, which, the blood flows from the superior and the inferior, vena cava into the atria and from there to the respective, ventricles through auriculoventricular valves., The complete cardiac cycle is comprised of following, events that take place in a sequential manner, , l, , l, , l, , l, , Atrial Systole, l, , l, , l, , A wave of contraction occurs from anterior to posterior, side stimulated by the SA node. The blood flows from the, pulmonary veins and vena cava into the left and right, ventricles, respectively as the tricuspid and bicuspid, valves are open., During this time the blood does not return to the great, veins (as blood is already present in them). The semilunar, valves are closed. The atrial systole increases the flow of, blood into the ventricles by about 30% (as 70% filling of, ventricles occurs passively during relaxation of ventricles,, before the atrial contraction)., At the end of the atrial systole, there start relaxation of, the atria (atrial diastole) and contraction of the ventricles, (ventricular systole) simultaneously. The atrial systole, occurs for 0.1s, while the atrial diastole on the other hand, is of about 0.7s., , This step involves the simultaneous relaxation of atria, (atrial diastole) and contraction of ventricles (ventricular, systole)., As the contraction of the ventricles begins, the pressure of, blood rises in them almost immediately (above the pressure, in the atria). This rapidly closes the atrioventricular valves,, in order to prevent the back flow of blood from ventricles to, atria., The conduction of action potential to the ventricular side, occurs by the AV node and AV bundle from where the, bundle of His transmits it through the entire ventricular, musculature. The contraction of ventricles thereby,, increases the ventricular pressure causing the closure of the, tricuspid and bicuspid valves due to attempted backflow of, blood into the atria., Finally, due to this, the increase in the pressure occurs in, the great arteries (i.e. pulmonary and aortic arches), so, semilunar valves guarding the pulmonary artery (right side), and the aorta (left side) are forced open and blood enters, through great arteries into ventricles., When ventricles relax (ventricular diastole), the ventricular, pressure falls which causes the closure of semilunar valves, preventing the backflow of blood into the ventricles., A further decline in the ventricular pressure, opens the, tricuspid and bicuspid valves by the pressure in the atria, exerted by the blood, which was being emptied into them by, the veins. This allows the blood to move freely to the, ventricles once again., The ventricles and atria are now again in a relaxed state, (joint diastole) as earlier. Soon, the SAN generates a new, action potential and the events described above sequencially, repeated to continue the process (next cardiac cycle)., , Heart Rate and Cardiac Output, l, , l, , l, , l, , We have just studied that, our heartbeats for about 72 times, per minute (on an average). This concludes that in a single, minute, many cardiac cycles are performed. Thus, deducing, that duration of a each cardiac cycle is 0.8 s., During each cardiac cycle (i.e. in one beat) each ventricle, pumps out about 70 mL of blood. This is known as stroke, volume., The volume of blood pumped out by each ventricle in one, minute is called cardiac output., We know that, in one minute heartbeats for 72 times. Thus,, cardiac output will be 5040 mL or approximately 5L in a, normal individual., Thus, Cardiac output = Stroke volume × Numbers of beats, /min.

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101, , CBSE Term II Biology XI, , Heart Sounds, , ii. QRS-Wave or Complex, , During each cardiac cycle, two prominent sounds are, produced which can be easily heard by a stethoscope (an, instrument used for the amplification of sound). This allows to, hear sounds and pulse of an individual. The basic reason for, the production of these sounds is the closure of various, valves. The sounds cardiac produced during each heartbeat, are as follows, , The Q, R and S wave together forms the QRS complex. This, represents the depolarisation of the ventricles, which, initiates the ventricular contraction., It marks the spread of impulse from AV node to ventricles,, through bundle of His and Purkinje fibres. The contraction, starts shortly after Q and marks the beginning of the systole., , i. LuBB, It is the first sound, being produced when inter, auriculoventricular valves (tricuspid and bicuspid valve) are, closed. This marks the end of the atrial systole and beginning, of ventricular systole., ii. DuPP, It is the second sound being produced when semilunar, valves (of aorta and pulmonary artery) get closed. This marks, the end of ventricular systole., , Electrocardiograph (ECG), l, , l, , l, , l, , It is a graphical representation of the electrical activity of, the heart during a single cardiac cycle. The, electrocardiogram is obtained by a machine known as, electrocardiograph. The study or the process of recording, of electrocardiogram is called electrocardiography., The impulse generated by the SA node causes contraction, and relaxation of heart chambers. To obtain an ECG, a, patient is connected to the machine with three electrical, leads (i.e. one to each wrist and one to the left ankle),, monitoring the activity of heart continuously and heart’s, functioning is evaluated by attaching multiple leads to the, chest region., An ECG consists of five peak, identified with the letter P to, T that corresponds to a specific electrical conductivity of, the heart., These corresponds to a specific electrical activity of the, heart as follows, , i. P-Wave, l, , It is the first and the foremost wave of low amplitude. It, represents the electrical excitation or depolarisation of, the atria which leads to contraction of both the atria., R, , P, , Q, , S, , T, , Diagrammatic representation of a standard ECG, , iii. T-Wave, It is a broad and smoothly rounded deflection, which, represents the return of the ventricles from excited to normal, state (repolarisation)., The end of T-wave marks the end of systole. It has been, observed that, by counting the number of QRS complexes,, that occur in a given time period, one can easily determine, the rate of heartbeat of an individual., However, the deviation in the ECG of any person from the, normal shape ECG, indicates a possible abnormality or a, disease., , Double Circulation, The mammalian heart is four-chambered, undergoing the, process of complete separate double circulation. This means, that blood passes twice through the heart to supply the blood, for once to the body. This transmission is neccessary, as it, helps in oxygenation of blood., The following processes constitute the double circulation, (i) Pulmonary Circulation In this system, blood completes, its circulation from right ventricle to the left atria, through the lungs. Here, the deoxygenated blood, pumped by the right ventricle enters the pulmonary, artery while, the left ventricle pumps blood into the, aorta., The deoxygenated blood is passed on to the lungs from, where, the oxygenated blood is carried out by the, pulmonary veins into the left atrium of heart., (ii) Systemic Circulation In this system, the pure blood is, supplied to all parts of the body. During transport, the, oxygenated (pure) blood entering the aorta is carried by, a network of arteries, arterioles and capillaries to the, tissues from where the deoxygenated (impure) blood is, collected by a system of venules, veins and vena cava,, thus, emptying it into the right atrium., This system provides essential nutrients, O 2 and other, essential substances to all the tissues of body and, eventually takes away CO 2 and other harmful, substances away from tissues for their elimination from, body., A unique vascular connection exists between the, digestive tract and liver called hepatic portal system.

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102, , CBSE Term II Biology XI, , The hepatic portal vein carries blood from intestine to, the liver before it is delivered to the systemic, circulation. A special coronary system of blood vessels, is present in our body exclusively for the circulation of, blood to and from the cardiac musculature., Lungs, , RA, , LA, , RV, , LV, , Dorsal aorta, , Heart, Smooth, muscles, , Lumen, Vein, , Lumen, Body parts, , Artery, , Capillary, , Smooth, muscles, , Schematic plan of bood circulation in human, , Regulation of Cardiac Activity, The normal activities of the heart are intrinsically regulated,, i.e. autoregulated by the specialised muscles, (nodal tissue)., Thus, the heart is known as myogenic heart., The neurogenic heartbeat is initiated by a nerve impulse, e.g., annelids and most arthropods. The rate of its formation and, conduction is regulated by the following, , 1. Neural Regulation, l, , l, , l, , Many diseases may affect the blood vessels and the normal, functioning of the heart., Some of the common disorders are as follows, , 1. High Blood Pressure (Hypertension), Pulmonary vein, , Pulmonary artery, Vena cava, (great vein), , Disorders of Circulatory System, , In medulla oblongata, a special neural centre is present,, which can moderate, the cardiac function through the, Autonomic Nervous System (ANS)., The neural signals through the sympathetic nerves (part of, ANS) increase the rate of heartbeat by stimulating SA node,, it also increases the strength of ventricular contraction and, thereby, the cardiac output., Whereas, the neural signal through parasympathetic, nerves (another component of ANS) can decrease the rate, of heartbeat by inhibiting the SA node, speed of conduction, of action potential, thereby decreasing the cardiac output., , 2. Hormonal Regulation, Adrenaline and nor-adrenaline hormones secreted by the, medulla of adrenal gland has significant role in regulating, heartbeat and thus increasing the cardiac output., The nor-adrenaline accelerates the heartbeat, while adrenaline, does this function at the time of emergency., , The pressure exerted by the flow of blood on the elastic walls, of the arteries is known as blood pressure. Hypertension is, the term used for blood pressure higher than the normal., The normal blood pressure in humans is measured as, 120/80 mmHg (millimetres of mercury pressure), in which, 120 mmHg is the systolic pressure (pumping pressure),, while, the 80 mmHg is the diastolic pressure (or resting, pressure)., Persistent increase in blood pressure above 140 mm Hg, (systolic) and 90 mm Hg (diastolic) is termed as hypertension., Condition of Hypertension, It may lead to many heart diseases and also affects vital, organs of the body, like the brain and kidney., , 2. Coronary Artery Disease (CAD), It is the hardening of arteries and arterioles due to the, thickening of the fibres tissue and the consequent loss of, elasticity. It is often referred to as atherosclerosis. This, mainly affects the vessels, which are mainly responsible for, supplying blood to the heart muscle. It seems to occur due to, deposition of calcium, fat cholesterol and fibrous tissues,, making the lumen of arteries narrower., , 3. Angina (Angina Pectoris), This tends to occur when enough oxygen does not reach the, heart muscles. It occurs both in men and women of any age, but seems to be more common among the middle-aged and, elderly individual. A symptom of acute chest pain occurs in, individual suffering from angina, which mainly occurs due to, the conditions that affect the bloodflow., , 4. Heart Failure, It is the condition of the heart when it fails to pump blood, effectively to meet the needs of the body. The heart failure is, sometimes called the congestive heart failure, as its main, symptom is congestion of lungs., , 5. Tachycardia and Bradycardia, Tachycardia is a term applied to a rapid heart or pulse rate, (over 100/min). Bradycardia is the term indicating a slow, heart or pluse rate (under 50/min).

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103, , CBSE Term II Biology XI, , Chapter, Practice, PART 1, Objective Questions, l, , Multiple Choice Questions, , 4. SA node is called the pacemaker of heart because, , 1. The percentage of water and protein in a straw, coloured viscous fluid, i.e. plasma is, (a) 92% and 8%, (b) 50% each, (c) 60% and 40%, (d) 32% and 68%, Ans. (a) Plasma is a faint yellow (straw coloured), slightly, alkaline viscous fluid. It consists of about 92% water, 1%, inorganic salts and 6-8% proteins. It constitutes about, 55% of the blood., , 2. Identify the following types of blood cells and mark, the correct option., , (a) it can change the contractile activity generated by, AV node, (b) it delays the transmission of impulse between the atria, and ventricles, (c) it gets stimulated when it receives neural signals, (d) it initiates and maintains the rhythmic contractile, activity of heart, Ans. (d) The contraction of the atria is initiated and activated, by Sino-Atrial node (SA node)., It is called pacemaker of the heart because it is, responsible for initiating and maintaining the rhythmic, contractile activity of heart., , 5. Identify A-F in the given diagram of human heart, and choose the correct option., , A, , B, , C, , A, , A, (a), (b), (c), (d), , Monocyte, Monocyte, Basophil, Basophil, , B, Eosinophil, Basophil, Blood platelets, Blood platelets, , C, Neutrophil, Neutrophil, Monocyte, Eosinophil, , Ans. (c), , E, B, , C, , D, F, , 3. If husband is Rh + and wife is Rh − then, (a) no problem with first child, (b) second child would have anaemia (erythroblastosis, foetalis), (c) second child would be normal, (d) Both (a) and (b), Ans. (d) The 1st child of Rh + husband and Rh − wife will be, normal, i.e. not having erythroblastosis foetalis due to the, absence of Rh antibodies in mother’s blood., The first child will be delivered safely, but now mother’s, blood identifies Rh + blood as antigen and prepares, antibodies against it to eliminate subsequent entry of this, antigen. Thus, second child would have erythroblastosis, foetalis., , (a) A–Vena cava, B–Right atrium, C–Left atrium, D–Right, ventricle, E–Left ventricle, F–Interventricular septum, (b) A–Vena cava, B–Right atrium, C–Right ventricle,, D–Left ventricle, E–Left atrium, F–Interventricular, septum, (c) A–Vena cava, B–Right atrium, C–Right ventricle,, D–Left atrium, E–Left ventricle, F–Interventricular, septum, (d) A–Vena cava, B–Left atrium, C–Right ventricle,, D–Left ventricle, E–Right atrium, F–Interventricular, septum, Ans. (b) A–Vena cava, B–Right atrium, C–Right ventricle,, D–Left ventricle, E–Left atrium, F–Interventricular septum

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104, , CBSE Term II Biology XI, , 6. The correct route through which pulse making, impulse travels in the heart is, (a) SA node → Purkinje fibres → Bundle of His →, AV node → Heart muscles, (b) SA node → AV node → Bundle of His → Purkinje, fibres → Heart muscles, (c) AV node → Bundle of His → SA node → Purkinje, fibres → Heart muscles, (d) AV node → SA node → Purkinje fibres → Bundle of, His → Heart muscles, Ans. (b), , Ans. (b) Statements II, III and IV are correct. Statement I is, , incorrect and can be corrected as, The closure of semilunar valves produces a highly, pitched and sharper Dupp sound. Closure of, atrio-ventricular valves produces, slow pitch Lubb sound., , 10. Given below is the diagrammatic representation of, standard Electrocardiogram (ECG). Identify the, figure which is the correct one., Q, , 7. Bicuspid and tricuspid valves open to allow, (a) blood from the pulmonary artery and vena cava to flow, into the left and right ventricles, respectively, (b) blood from the pulmonary vein and vena cava to flow, into left and right ventricles, respectively, (c) blood from the pulmonary vein and vena cava to flow, into left and right atrium, respectively, (d) oxygen from the pulmonary vein and vena cava to flow, into left and right atrium, respectively, Ans. (b) During joint diastole, all the four chambers of heart, are in a relaxed state. This causes the tricuspid and, bicuspid valves to open and blood from the pulmonary, veins and vena cava to flow into the left and the right, ventricles, respectively through the left and right atria., The semilunar valves are closed at this stage., , S, , P, , R, , (a), , T, S, , P, , (b), , Q, R, , T, , R, , T, P, , Q, , S, , (c), R, , 8. Cardiac output is, (a) volume of the blood pumped out by each ventricle per, minute, (b) volume of the blood contained in the entire heart, (c) volume of the oxygenated blood pumped by heart, (d) volume of the deoxygenated blood pumped by heart, Ans. (a) Cardiac output is volume of the blood pumped out by, the ventricles per unit minute. It is calculated as, Cardiac output = Stroke volume × Heart rate/Heartbeat., , 9. Which of the following statements are correct?, I. Closure of atrioventricular valves produces ‘Dupp’, sound., II. A cardiac cycle consists of a systole and a diastole, of both atria and ventricles., III. The average number of the times, a normal, heartbeats in one minute is 72., IV. Change in the blood volume in all the chambers of, the heart occurs during the cardiac cycle., , The option with correct statements is, (a), (b), (c), (d), , I, II and III, II, III and IV, I, II and IV, I, III and IV, , T, P, , Q, , S, , (d), , Ans. (d) ECG is a graphical representation of the electrical, , activity of the heart during a cardiac cycle. Option (d), correctly represents standard Electrocardiogram (ECG)., , 11. Match the following columns., Column I, (ECG Wave), A. P-wave, , Column II, (Features), 1. Depolarisation of ventricles, , B. QRS complex, , 2. Repolarisation of ventricles, , C. T-wave, , 3. Coronary ischemia, , D. Reduction in size of, T-wave, , 4. Depolarisation of atria, , Codes, A B C D, (a) 4 1 3 2, (b) 2 3 1 4, (c) 2 1 3 4, (d) 4 1 2 3, Ans. (d) A–4, B–1, C–2, D–3

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105, , CBSE Term II Biology XI, , 12. Pulmonary circulation is, , l, , (a), , Left, auricle, , Oxygenated, blood, , Lungs, , Deoxygenated, blood, , (b), , Left, auricle, , Deoxygenated, blood, , Lungs, , Oxygenated, blood, , Right, ventricle, Right, ventricle, , Left, Right Deoxygenated Lungs Oxygenated, blood, blood, auricle, ventricle, Oxygenated, Deoxygenated Left, (d) Right, Lungs, blood, blood, ventricle, auricle, Ans. (c), (c), , 13. Neural centre in medulla oblongata can moderate, the cardiac function through, (a) ANS (Autonomic Nervous System), (b) sympathetic nervous system, (c) parasympathetic nervous system, (d) somatic nervous system, Ans. (a) Neural centre in medulla oblongata can moderate the, cardiac function through ANS (Autonomic Nervous, System)., , 14. Atherosclerosis is caused by deposition of, (a) calcium, (b) fat and cholesterol, (c) fibrous tissue, (d) All of these, Ans. (d) Coronary artery disease, often referred to as, atherosclerosis, affects the vessels that supply blood to, the heart muscle. It is caused by deposition of calcium,, fat, cholesterol and fibrous tissues, which makes the, lumen of arteries narrower., Thus, option (d) is correct., , 15. Match the following columns., Column I, (Cardiac Disorders), , Column II, (Features), , A., , Heart failure, , 1. Heart muscle is suddenly damaged, by an inadequate blood supply, , B., , Cardiac arrest, , 2. Chest pain due to inadequate O2, reaching the heart muscles, , C., , Heart attack, , 3. Heart not pumping blood, effectively enough to meet the, needs of the body, , D., , Angina pectoris 4. Heart stops beating, , Codes, A B C D, (a) 3 4 1 2, (b) 4 3 1 2, (c) 3 4 2 1, (d) 4 3 2 1, Ans. (a) A–3, B–4, C–1, D–2, , Assertion-Reasoning MCQs, Direction (Q. Nos. 1-5) Each of these questions contains, two statements, Assertion (A) and Reason (R). Each of, these questions also has four alternative choices, any one, of which is the correct answer. You have to select one of, the codes (a), (b), (c) and (d) given below., (a) Both A and R are true and R is the correct, explanation of A, (b) Both A and R are true, but R is not the correct, explanation of A, (c) A is true, but R is false, (d) A is false, but R is true, , 1. Assertion (A) Reduction in number of platelets can, lead to excessive loss of blood from the body in case, of injury., Reason (R) Platelets help in the coagulation of, blood., Ans. (a) Both A and R are true and R is the correct explanation, , of A., , 2. Assertion (A) Thrombin is essential for blood, clotting., Reason (R) Ca 2+ plays an important role in blood, clotting., Ans. (b) Both A and R are true, but R is not the correct, , explanation of A., , 3. Assertion (A) The heart rate of a six months old, baby is much higher than that of a normal adult, person., Reason (R) Smaller the organism, higher is the rate, of metabolism per gram weight., Ans. (a) Both A and R are true and R is the correct explanation, , of A., , 4. Assertion (A) Bundle of His is a part of, autoexcitable tissue., Reason (R) This region comprises of cardiac tissue, that can generate impulse on its own at a frequency, less than SA node., Ans. (a) Both A and R are true and R is the correct explanation, , of A., , 5. Assertion (A) The end of T-wave marks the end of, ventricular systole., Reason (R) T-wave represents the return of, ventricles from excited to normal state which is, repolarisation., Ans. (a) Both A and R are true and R is the correct explanation, , of A.

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106, l, , CBSE Term II Biology XI, , Case Based MCQ, 1. Direction Read the following passage and answer, the questions that follows., Human heart is a muscular organ which serves as a, pump to circulate the blood in whole body tissues., It has four chambers and several valves help which, to regulate the normal blood flow within body. The, valves that separate the atria from the ventricle are, either tricuspid or bicuspid. Valves of ventricular, outlets are semilunar valves. These valves are, anchored to heart muscles through, tendon-resembling fibrous cords of connective, tissue. Heart pumps blood through three divisions, of circulatory system, viz. the coronary, pulmonary, and systemic. The blood vessels in these systems, are separated to ensure complete separation of, oxygenated and deoxygenated blood., (i) Bicuspid valves are found between, , (a) right ventricle and right auricle, (b) right ventricle and left auricle, (c) left ventricle and left auricle, (d) right ventricle and left auricle, Ans. (c) Bicuspid valves are found between left auricle and left, ventricle., , (ii) Opening of right ventricle into pulmonary artery is, guarded by, (a) bicuspid valve, (b) tricuspid valve, (c) semilunar valve, (d) mitral valve, Ans. (c) Opening of right ventricle into pulmonary artery is, guarded by semilunar valves., , (iii) Left atrium receives blood from lungs through, (a) pulmonary vein, (b) aorta, (c) pulmonary artery, (d) vena cava, Ans. (a) Pulmonary veins pour blood from the lungs to left, atrium. It is the only vein that carry oxygenated blood., , (iv) The coronary circulations supply blood to, (a) skeletal muscles, (b) cardiac muscles, (c) smooth muscles, (d) All of these, Ans. (b) Coronary vessels supply blood to heart (cardiac), muscles., , (v) Interatrial septum is, (a) thin and muscular wall between two atria, (b) thick wall between two atria, (c) fibrous opening of atria, (d) muscular flap near the opening of atria, Ans. (a) Human heart is four-chambered, with a thin muscular, wall called the interatrial septum separating the right and, the left atria., , PART 2, Subjective Questions, l, , Short Answer (SA) Type Questions, 1. Why do we consider blood as a connective tissue?, (NCERT), , Ans. Blood is a mobile connective tissue derived from, , mesoderm. It consists of fibre-free fluid matrix, plasma, and other cells. It is called so, as it regularly circulates in, the body and takes part in transport of materials., , 2. What is the importance of plasma proteins?, (NCERT), Ans. Fibrinogen, globulins and albumins are the major plasma, , proteins. Fibrinogens (present in insoluble form) are, needed for clotting or coagulation of blood. Globulins, primarily are involved in defence mechanisms of the body, and the albumins help in osmotic balance., , 3. State the functions of the following in blood, (i) Fibrinogen, (iii) Neutrophils, , (ii) Globulin, (iv) Lymphocytes, (NCERT Exemplar), , Ans. Functions of the following are, , (i) Fibrinogens are needed for clotting or coagulation of, blood at the site of injury to stop bleeding., , (ii) Globulins are primarly involved in immunity, i.e., defence mechanisms of the body (to fight infections)., (iii) Neutrophils and monocytes are phagocytic cells, which destroy foreign organisms entering the body, and then blood stream., (iv) Lymphocytes provide immunity to the body., , 4. Name the components of the formed elements in, the blood and mention one major function of each, of them., (NCERT), Ans. The components of formed elements in the blood are, , (i) Erythrocytes (RBCs) These are the most abundant, of all the cells found in the body. RBCs contain, respiratory pigment, i.e. haemoglobin which acts as, an oxygen carrier., (ii) Leucocytes (WBCs) These are known to be the most, active and motile constituent. They are colourless., They defend the body against infections and, diseases., (iii) Blood Platelets (Thrombocytes) These are cell, fragments produced from megakaryocytes. These are, mostly involved in coagulation or clotting of blood.

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107, , CBSE Term II Biology XI, , through the closed system and return to the heart. This, fastens the supply and removal of materials to and from, the tissues by the blood., , 5. One of the ABO blood groups is sometimes called, the universal donor. Which group do you think it is, and why?, Ans. Individuals with blood group O are called universal, , donors. These individuals do not have either A or B, antigens on the surface of their RBCs, but their blood, serum contains antibodies against both A and B antigens., Therefore, group individuals can only receive blood from, a group O individuals, but they can donate blood to, individuals of any ABO blood group (i.e. A, B, O or AB)., , 6. An Rh – woman is carrying an Rh + foetus for the, second time. Describe the consequences of, Rh – incompatibility in this case?, Or What physiological circumstances lead to, erythroblastosis foetalis?, (NCERT Exemplar), Ans. Rh-antigen is present on the surface of erythrocytes in, , about 80-85% of the human beings. The individuals, who, possess this antigen are called Rh + (Rh positive) and, those, who do not have it are called Rh − (Rh negative)., A person when exposed to Rh + blood, develops anti Rh, antibodies., A pregnant woman who is Rh − , if bears an Rh + foetus,, will develop anti-Rh antibodies during the first delivery,, when the foetal blood comes in contact with her blood. If, she carries a second foetus, that is Rh + , the anti-Rh, antibodies in her blood enter the foetal circulation and, cause damage to the foetal RBCs. This, could become, fatal. This condition is called erythroblastosis foetalis., , 7. Write the Differences between, (i) Open and closed system of circulation, (ii) P-wave and T-wave, , (NCERT), Ans. (i) Difference between open and closed circulatory, , system is, Open Circulatory System Closed Circulatory System, The blood is pumped by the, heart into the blood vessels, that open into blood spaces, (sinuses)., Here, blood is in direct, contact with the tissues., , The blood is pumped by the, heart into closed blood, vessels., Here, blood is not in the, direct contact with the, tissues., , (ii) Difference between P-wave and T-wave is, P-wave, , T-wave, , This wave represents the, electrical excitation, (or depolarisation) of the, atria, which lead to the, contraction of both the, atria., , This wave represents the, return of the ventricles from, excited to normal state, (repolarisation). The end of, the T-wave marks the end of, systole., , 8. Why is closed circulatory system more efficient, than the open system?, (HOTS), Ans. The closed circulatory system considerably enhances the, speed, precision and efficiency of circulation. The blood, flows far more rapidly, it takes less time to circulate, , 9. A fish’s heart pumps only deoxygenated blood,, why?, (HOTS), Ans. A fish’s heart pumps only deoxygenated blood as it is a, two-chambered with an atrium and a ventricle. The heart, pumps out deoxygenated blood which is oxygenated by, the gills and supplied to other body parts, from where, deoxygenated blood is returned to the heart., , 10. Answer the following, (i) Name the major site where RBCs are formed., (ii) Which part of heart is responsible for initiating, and maintaining its rhythmic activity?, (iii) What is specific in the heart of crocodiles among, reptilians?, (NCERT Exemplar), Ans., , (i) Major site where RBCs are formed is bone marrow., (ii) Sinoatrial node (SA node) is responsible for initiating, and maintaining rhythymic activity of the heart., (iii) Reptiles have three-chambered heart except, crocodile, which has four-chambered heart., , 11. Differentiate between right ventricle and left, ventricle., Ans. Differences between right ventricle and left ventricle are, , as follows, Right Ventricle, , Left Ventricle, , It is smaller than the left, ventricle., , It is comparatively larger, than right ventricle., , Receives and pushes, deoxygenated blood., , Receives and pumps, oxygenated blood., , It receives blood from the right It receives blood from the, atrium and send it to the lungs left atrium and send it to, via pulmonary artery., various body parts via aorta., It belongs to the pulmonary, circulation., , It belongs to the systemic, circulation., , 12. Differentiate between arteries and veins., Ans. Differences between arteries and veins are as follows, , Arteries, , Veins, , They carry blood from the, They bring back blood, heart to the different parts of from different parts of the, the body., body to the heart., The wall of arteries are thick The wall of the veins are, and muscular., thin and non-muscular., They are usually deep seated. They are situated, superficially under skin., Except the pulmonary, Except pulmonary veins, arteries, all the arteries carry all the veins carry, oxygenated blood., deoxygenated blood., Arteries have no valves., , Veins have valves to, prevent backflow of the, blood.

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108, , CBSE Term II Biology XI, , 13. What is the significance of atrioventricular node, and atrioventricular bundle in the functioning of, heart?, (NCERT), Ans. Atrioventricular node or AV node is the mass of tissues, , seen in the lower left corner of the right atrium close to, the atrioventricular septum., They strengthen the signals which arise from the SA, nodes as these signals become weak because ventricles, are far away from SA nodes. While the atrioventricular, bundle (AV bundles) which originates from the AV nodes, conveys the cardiac impulse further towards the walls of, ventricles., , 14. What happens to the mitral valve and the related, blood flow during ventricular systole?, Ans. At the start of the ventricular systole, the mitral valve, , closes to prevent the flow of blood back into the atrium., As systole continues, blood from the right ventricle enters, the pulmonary artery and blood from the left ventricle, enters the aorta., , 15. Sinoatrial node is called the pacemaker of our, heart. Why?, Ans. The SA node consists of a cluster of cells that are situated, , in the upper parts of the wall of the right atrium., Sinoatrial node of heart is responsible for initiating and, maintaining the rhythmic activity, therefore it is known as, pacemaker of the heart., , 16. Differentiate between SA node and AV node., Ans. Differences between SA node and AV node are as follows, , SA Node, , AV Node, , It is located at the upper, lateral wall of right auricle., , It is situated at the base of, right auricle, near, auriculoventricular junction., It generates impulses to, Normally it does not, initiate heart beating., generate impulse, but, strengthen them., SA node is also called, AV node is also called, pacemaker., pacesetter., It supplies signals directly to It supplies signals to, auricles., ventricles., It is not associated with, It is associated with bundle, bundle of His and Purkinje of His and Purkinje fibres., fibres., , 17. What are the two heart sounds heard through, stethoscope? How is each of these produced?, Or What are two heart sounds? When and how are, these sounds produced?, Or Explain heart sounds., (NCERT), Ans. We can hear with a stethoscope, the two main heart, , sounds (i.e. Lubb and Dupp), which repeat rhythmically., These sounds result from the closure of the heart valves., The first sound (Lubb), which is of longer duration, , (0.16-0.90 s) and a louder one is created by the closure of, the atrioventricular valves immediately after the start of, the ventricular systole. The second sound is of shorter, duration (0.10 s) and is created by the closure of the, semilunar valve at the end of the ventricular systole., , 18. Mention phases of blood pressure, when are they, seen?, Ans. Phases of blood pressure are, , (i) Systolic Blood Pressure It is seen during the, contraction of left ventricle., (ii) Diastolic Blood Pressure It is seen during the, relaxation of left ventricle., , 19. If a patient’s ECG reveals an abnormally long delay, between the P-wave and the QRS deflection, what, does this suggest?, Ans. If a patient’s ECG reveals an abnormally long delay, , between P-wave and the QRS deflection, it suggests that, there is a delay of conduction from the atria to the, ventricles. Hence, the stimulation from SA nodes are, conducting stimuli to the ventricles very slowly., , 20. What is meant by P-Q interval and S-T interval in, electrocardiography?, Ans. In electrocardiography, P-Q interval (also called PR, , interval) is the time taken by the impulse to travel, through atria, AV node and the rest of the conducting, tissues. The normal P-R interval lasts for about 0.16 s. The, S-T interval is the representation of time between the end, of the spread of impulse through ventricles and its, repolarisation., , 21. Write a short note on Electrocardiogram (ECG)., Ans. Electrocardiogram (ECG) is a graphical representation of, , the electrical activity of the heart during a single cardiac, cycle., The impulse generated by the SA node causes contraction, and relaxation of heart chambers. To obtain an ECG, a, patient is connected to the machine with three electrical, leads (i.e. one to each wrist and one to the left ankle),, monitoring the activity of heart continuously and heart’s, functioning is evaluated by attaching multiple leads to the, chest region., An ECG consists of five peak, i.e. P-wave (electrical, excitation or depolarisation of atria), QRS-wave, (depolarisation of ventricles), T-wave (repolarisation)., R, , P, , Q, , S, , T, , However, deviation in the ECG of any person from the, normal shape of ECG indicates a possible abnormality or, a disease.

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109, , CBSE Term II Biology XI, , It passes towards the left and right ventricles and thus, no, oxygenated and deoxygenated blood is mixed. The, ventricles pump oxygenated and deoxygenated blood, without mixing. Thus, two separate circulatory pathways, are found and this type of blood circulation is called as, double circulation, which includes systemic and, pulmonary circulation., , 22. Explain double circulation with the help schematic, diagram., Ans. Flowchart of double circulation, Pulmonary, veins, Right, atrium, , Capillaries of, lungs, , Branches of, pulmonary artery, , Superior and, inferior vena cava, , Heart, Left, atrium, , Right, Left, ventricle ventricle, , Pulmonary, artery, , Tissue, capillaries, , 25. What is the significance of hepatic portal system in, the circulatory system?, (NCERT Exemplar), Ans. A unique vascular connection exists between the, digestive tract and liver called hepatic portal system. The, hepatic portal vein carries blood from intestine to the, liver before it is delivered to the systemic circulation., This ensures that the liver, which has the metabolic, versatility to interconvert various organic molecules has, first access to nutrients after the food is digested., , Branches of, dorsal aorta, , Aorta, , 23. Differentiate between pulmonary and systemic, circulation., , 26. Write a note on regulation of cardiac activity., Ans. The normal activities of the heart are intrinsically, , Ans. Differences between pulmonary circulation and systemic, , regulated, i.e. autoregulated by the specialised muscles,, (nodal tissue). Thus, the heart is known as myogenic, heart., The rate of its formation and conduction is regulated by, the following, 1. Neural Regulation In medulla oblongata, a special, neural centre is present, which can moderate the, cardiac function through the Autonomic Nervous, System (ANS). The neural signals through the, sympathetic nerves (part of ANS) increase the rate, of heartbeat by stimulating SA node, it also increases, the strength of ventricular contraction and thereby,, the cardiac output. Whereas, the neural signal, through parasympathetic nerves (another, component of ANS) can decrease the rate of, heartbeat by inhibiting the SA node, speed of, conduction of action potential, thereby decreasing, the cardiac output., 2. Hormonal Regulation Adrenaline and, nor-adrenaline hormones secreted by the medulla of, adrenal gland has significant role in regulating, heartbeat and thus increasing the cardiac output., The nor-adrenaline accelerates the heartbeat, while, adrenaline does this function at the time of, emergency., , circulation are as follows, Pulmonary Circulation, , Systemic Circulation, , It is smaller circuit, which, carries blood to the lungs, and back to the heart., , It is a larger circuit, which, supplies blood to the various, parts of the body and back to, the heart., It supplies oxygenated blood to, all parts of the body., , It carries deoxygenated, blood to the lungs for, oxygenation., The blood is pumped by, The blood is pumped by left, right ventricle and received ventricle and received by the, by left atrium., right atrium., , 24. Explain the advantage of the complete partition of, ventricle among birds and mammals and hence, leading to double circulation., Ans. The birds and mammals have evolutionary advancement, , as far as structure of heart is concerned. They need more, oxygen to live in terrestrial habitat., In these animals, the blood received by left and right, auricles is oxygenated and deoxygenated, respectively., Pulmonary trunk aorta, , 27. Given below are the abnormal conditions related to, , RA, , blood circulation. Name the disorders., (i) Acute chest pain due to failure of oxygen supply to, heart muscles., (ii) Increased systolic pressure., (NCERT Exemplar), , Atrioventricular, septum, RV, , LV, , Ans., Heart of Bird/Mammal, , (i) Angina, (ii) High blood pressure

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110, l, , CBSE Term II Biology XI, , Long Answer (LA) Type Questions, 1. What is the differences between blood and lymph?, , Ans. Differences between blood and lymph are as follows, , Blood, , Lymph, , It is red in colour due to the, It is colourless as red blood, presence of haemoglobin in red cells are absent., cells., It consists of plasma, RBCs,, WBCs and platelets., , It consists of plasma and very, low number of WBC., , Glucose concentration is low., , Glucose concentration is, higher than blood., , Clotting of blood is a fast, process., , Clotting of lymph is, comparatively slow., , It transports materials from one It transports materials from, organ to other., tissue cells into the blood., Flow of blood is fast., , Lymph flows very slowly., , Its plasma has more proteins,, calcium and phosphorus., , Its plasma has less protein,, calcium and phosphorus., , It moves away from the heart, and towards the heart., , It moves in one direction, i.e., from tissues to subclavians., , 2. Write the composition of blood. Explain the, functions of blood cells., Ans. Blood is a special connective tissue comprising of a fluid, , matrix, plasma and formed elements., Plasma, It is a straw coloured, viscous, slightly alkaline aqueous, body fluid. It forms about 55% of the blood., It is composed of many organic and inorganic, substances. It contains 90-92% water and 6-8% solutes, in it., Factors for clotting or coagulation of blood are also, present actively in the plasma. Plasma without the, blood clotting factors is called serum., Formed elements, The formed elements or blood corpuscles include, erythrocytes, leucocytes and platelets. These constitute, about 45% of the blood., 1. Erythrocytes (Red Blood Corpuscles), These are the most abundant of all cells found in the, blood. They are red in colour due to the presence of a, pigment called haemoglobin, which acts as an oxygen, carrier. The formation of RBCs takes place in the, red bone marrow in adults., RBCs have an average lifespan of 120 days after which, they are destroyed in the spleen (graveyard of RBCs)., 2. Leucocytes (White Blood Corpuscles), These are known to be the most active and motile, constituent of blood as well as lymph. They do not, possess the red colour pigment (haemoglobin) in them, so, they are colourless in nature., These are nucleated and are generally short-lived cells., n, , n, , Leucocytes or white blood corpuscles are categorised into, two main categories such as, i. Granulocytes They contain granules in the, cytoplasm and have regularly lobed nucleus. The, granulocytes are further subdivided into three main, types, (a) Neutrophils These are the most abundant cells, (about 60-65%) of the total WBCs. These are, phagocytic cells that destroy foreign organisms, entering the body., (b) Eosinophils They are characterised by their, bilobed nucleus. They are about 2-3% of total, WBCs. They resist infections and are also, associated with all allergic reactions. They also, help in dissolving blood clot. They help to, destroy the toxic substances present in the body., (c) Basophils They contain fewer coarse granules, than the eosinophils. They are found least, abundantly (0.5-1.0%) among WBCs. They, secrete histamine, serotonin, heparin, etc., and, are involved in inflammatory reactions., ii. Agranulocytes They lack granules in their cytoplasm, and have rounded or oval nucleus. Agranulocytes are, also further subdivided into two main types, (a) Lymphocytes These are smaller in size and have, rounded nucleus. Lymphocytes are of further, two types, i.e. B-cells and T-cells. Both of these, (i.e. B and T-cells) are responsible for immune, responses of the body., (b) Monocytes These are largest of all types of, WBCs, but are fewer in number. Mature, monocytes are known as macrophages. They, help to kill foreign particles. These are, phogocytic in nature., , n, , 3. Explain different types of blood groups and donor, compatibility making a table., , (NCERT Exemplar), , Ans. Two groupings, i.e. the ABO and Rh are widely used all, , over the world. ABO grouping is based on the presence, or absence of two surface antigens (chemicals that can, induce immune response) on the RBCs, i.e. A and B., Similarly, the plasma of different individuals contain two, natural antibodies (proteins produced in response to, antigens)., Blood Groups and Donor Compatibility, Blood Group, A, , Antigen on, RBCs, , Antibody in Donor’s, Plasma, Group, , A, , Anti-B, , A, O, , B, , B, , Anti-A, , B, O, , AB, , A, B, , Nil, , AB, A, B, O, , O, , Nil, , Anti- A, B, , O, , From the mentioned table it is evident that group ‘O’, blood can be donated to persons with any other blood, group and hence ‘O’ group individuals are called

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111, , CBSE Term II Biology XI, , ‘universal donors’. Persons with ‘AB’ group can accept, blood from persons with AB as well as the other groups of, blood. Therefore, such persons are called ‘universal, recipients’., , 4. Thrombocytes are essential for coagulation of, blood. Comment., (NCERT Exemplar), Or Describe the process of blood clotting in detail., Ans. Thrombocytes are small fragments of megakaryocytes, , found in red bone marrow these are essential for, coagulation or clotting of blood which involves following, steps, (i) Thromboplastin helps in the formation of an, enzyme prothrombinase (which inactivates heparin), that converts the inactive plasma protein, i.e., prothrombin into its active form thrombin., (ii) Thrombin thus, acts as a proteolytic enzyme to, convert fibrinogen molecule (produced from the, liver in the presence of vitamin-K) to form insoluble, fibrin monomer. This reaction required, thrombokinase an enzyme complex, which is formed, by a series of linked enzymatic reactions (with, cascade effects) which involves a number of various, factors present in the plasma in their inactive state., Both the changes mentioned above require Ca 2+, ions for their reaction., Blood platelets, , Injured tissue, Releases, , Disintegrate, , Thromboplastin, , Platelet factor-3, (platelet thromboplastin), , Ca2+ proteins, , Ca2+ proteins, Prothrombinase, , Step I, , Inactivates heparin, and catalyses, , Step II, , Prothrombin, , Step III, , Fibrinogen, , Ca2+, , (Fibrin + Blood cells), , Thrombin, catalyses, Fibrin, Clot, , Role of thrombocytes in blood coagulation, , (iii) These fibrin monomers polymerise to long, sticky, fibres. The fibrin threads form a fine network of, threads called fibrins, in which dead and damaged, formed elements of blood are trapped., This finally leads to the formation of a clot or, coagulum, which is a dark reddish-brown scum, formed over the surface of injury., , 5. Describe the evolutionary change in the pattern of, heart among the vertebrates., (NCERT), Ans. The heart among the vertebrates shows different patterns, of evolution. Different groups of animals have evolved, different methods for this transport. All vertebrates, possess a muscular chambered heart., (i) Fishes have a two-chambered heart with an atrium, and a ventricle. The heart pumps out deoxygenated, , blood which is oxygenated by the gills and supplied, to the body parts from where deoxygenated blood is, returned to the heart., (ii) Amphibians and the reptiles (except crocodiles) have, a three-chambered heart with two atria and a single, ventricle. The left atrium receives oxygenated blood, from the gills/lungs/skin and the right atrium gets, the deoxygenated blood from other body parts., However, they get mixed up in the single ventricle, which pumps out mixed blood., (iii) Crocodiles, birds and mammals possess a, four-chambered heart with two atria and two, ventricles. Oxygenated and deoxygenated blood, received by the left and right atria, respectively, passes on to the ventricles of the same sides. The, ventricles pump it out without any mixing up, i.e., two separate circulatory pathways are present in, these organisms, hence these animals have double, circulation., , 6. Describe briefly the external structure of human, heart with neat and labelled diagram., Ans. Heart is a mesodermally derived organ, situated in the, , thoracic cavity in between the two lungs. It appears to be, slightly tilted towards the left side. It is a hollow,, fibromuscular organ, slightly conical in shape of about, 12 cm length and 9 cm breadth. The upper broad part is, called the base and the lower narrow part is known as the, apex. It has a size of a clenched fist., Right subclavian artery, Right common carotid artery, Superior vena cava, Ascending aorta, Right pulmonary artery, Right pulmonary, veins, , Brachiocephalic artery, Left common carotid artery, Left subclavian artery, Arch of aorta, Descending aorta, Ligamentum arteriosum, Pulmonary artery (left), Pulmonary veins (left), , Right atrium, , Pulmonary trunk, Left atrium, , Coronary artery, (in coronary sulcus), Right ventricle, , Anterior, interventricular, sulcus, , Inferior vena cava, , Left ventricle, , Descending aorta, , External structure of human heart, , The heart is protected by a double-walled membranous, sac or a bag called pericardium. The fluid present, between two membrane is called pericardial fluid. This, fluid helps in keeping the surface of the heart moist and, also protects it from shock and mechanical injuries.

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112, , CBSE Term II Biology XI, , Externally, the human heart is composed of four, chambers, i.e. two relatively small upper chambers called, auricles (sing. atria) and two larger lower chambers called, ventricles., The right atrium is slightly larger than the left atrium., Both these atria are meant to receive blood from different, body parts., , 7. Describe briefly the internal structure of human, heart with neat and labelled diagram., Or Draw a diagram to show the internal structure of, human heart. Label six parts in all including three, valves., , (ii) Bicuspid Valve (Mitral valve) It is the type of valve, that guards the opening between the left atrium and, the left ventricle., (iii) Semilunar Valve The opening of the right and the, left ventricles into the pulmonary artery and the, aorta, respectively are provided with the semilunar, valves., , 8. (i) What is cardiac output and how it is calculated., (ii) Why is the left ventricular wall thicker than the, right ventricular wall in the human heart?, (iii) Explain cardiac cycle in brief., Ans., , Ans. The internal chamber of heart consist of two auricles, , (atria) and ventricles which are separated by different, septa and valves., (i) Auricles are the upper thin walled and small, chambers which receive the blood hence, called, receiving chambers (right and left atrium). Right, atrium receive impure or deoxygenated blood from, vaious parts of body through superior and inferior, vena cava while left atrium recieve pure or, oxygenated blood from lungs through pulmonary, veins., (ii) Ventricles are the lower two chambers of heart, which pump blood away from the heart hence called, pumping chamber. Right ventricle receives impure, or deoxygenated blood from right atrium and pump, it to pulmonary artery, which takes blood to lungs., Left ventricles receive oxygenated blood from left, atrium and pump it into aorta which takes blood to, whole body., Cardiac valves are membranous door-like structure in, the heart that serves to maintain the unidirectional flow, of blood., Arch of, aorta, , Superior vena cava, , Pulm, arter onary, y, , Right pulmonary, artery, Right pulmonary, veins, Pulmonary, semilunar valve, Right atrium, , Left pulmonary artery, , 9. Briefly describe the followings, Left pulmonary veins, Left atrium, Aortic semilunar valve, Left atrioventricular, valve (bicuspid valve), , Right, atrioventricular, valve, (tricuspid valve), , Left ventricle, Chordae tendineae, , Right ventricle, Inferior, vena cava, , (i) The volume of blood pumped out by each ventricle, in one minute is called cardiac output., Cardiac output can be calculated as, = Stroke volume × Numbers of beats /min., Where, stroke volume is the volume of blood, pumped out by each ventricle during each cardiac, cycle, i.e. 70 mL., In one minute heartbeats for 72 times then cardiac, output will be, ⇒ 70 × 72 ⇒ 5040 mL or 5L approximately., (ii) This is because the left ventricle is required to pump, oxygenated blood all over the body, while the right, ventricle needs to pump deoxygenated blood to the, nearby lungs only., (iii) A cardiac cycle is defined as the sequence of, alternating contraction and relaxations of the atria, and ventricles in order to pump blood through out, the body. The phase of contraction is known as, systole, while the relaxation phase is called the, diastole. Thus, a single heartbeat consists of a systole, and diastole of both the atria and the ventricles., To begin with the cardiac cycle, all four chambers of, heart are in a relaxed state, i.e. they are in joint, diastole, during which, the blood flows from the, superior and the inferior vena cava into the atria, and from there to the respective ventricles through, auriculoventricular valves., , Aorta Papillary muscle, , Interventricular, septum, , Internal structure of human heart, , Different valves present in the heart are given below, (i) Tricuspid Valve It is formed by three muscular, flaps or cusps to guard the opening between the, right atrium and the right ventricle., , (i) Anaemia, (iii) Atherosclerosis, (v) Heart failure, Ans., , (ii) Angina pectoris, (iv) Hypertension, (NCERT Exemplar), , (i) Anaemia is a condition in which the blood lack red, blood cells to carry sufficient amount of oxygen to, body. This reduced O2 level can lead to symptoms, such as fatigue, weakness, pale skin colour, low, haemoglobin tiredness, etc., (ii) Angina (Angina Pectoris) This tends to occur when, enough oxygen does not reach the heart muscles. It, occurs both in men and women of any age but seems, to be more common among the middle-aged and, elderly individual. A symptom of acute chest pain, occurs in individual suffering from angina, which, mainly occurs due to the conditions that affect the, blood flow.

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113, , CBSE Term II Biology XI, , (iii) Atherosclerosis refers to the irregular thickening of, arterial walls and narrowing of lumen due to, deposition of anthromas, i.e. cholesterol and lipid, material. Due to this the supply of blood delievered to, brain is decreased leading to stroke., (iv) Hypertension is the term used for blood pressure, higher than the normal. The normal blood pressure in, human is measured as 120 mm Hg (systolic pressure), by 80 mm Hg (diastolic pressure). Persistent increase, in blood pressure above 140 mm Hg/90 mm Hg is, termed as hypertension., (v) Heart failure is the condition of the heart when it fails, to pump blood effectively to meet the needs of the, body. The heart failure is sometimes called the, congestive heart failure, as its main symptom is, congestion of lungs., , 10. Write short note on the following, (i) Bradycardia and tachycardia, (ii) Coronary artery disease, Ans. (i) Bradycardia and Tachycardia Bradycardia is the, term indicating a slow heart or pulse rate (under, 50/min). Tachycardia is a term applied to a rapid heart, or pulse rate (over 100/min)., (ii) Coronary artery disease is the hardening of arteries, and arterioles due to the thickening of the fibres tissue, and the consequent loss of elasticity. It is often, referred to as atherosclerosis. This mainly affects the, vessels, which are mainly responsible for supplying, blood to the heart muscle. It seems to occur due to, deposition of calcium, fat cholesterol and fibrous, tissues, making the lumen of arteries narrower., l, , Case Based Questions, 1. Direction Read the following passage and answer the, questions that follows., In a biology lecture, teacher told students that, human heart is highly evolved and complex organ. It, pump blood around the body and prevent the mixing, of oxygenated and deoxygenated blood. It also act, like one way traffic system to ensure that blood, travels in one direction, due to the presence of valves, in it., (i) Name the septum which prevent the mixing of, oxygenated and deoxygenated blood in heart., , Ans. Inter atrial septum and inter ventricular septum separate, , the atria and ventricles, respectively. The right side of heart, contain deoxygenated blood whereas left side contain, oxygenated blood., , (ii) Name the blood vessels which (a) supply oxygenated, blood throughout the body,, (b) supply deoxygenated blood to lungs., Ans. (a) Aorta, (b) Pulmonary artery, , (iii) Name the artery which carry deoxygenated blood, and the vein which carry oxygenated blood., Ans. Pulmonary artery carry deoxygenated blood from right, , ventricles whereas pulmonary vein carry oxygenated, blood to left atrium from lungs., , (iv) Where does the tricuspid and bicuspid valves are, found in human heart?, Ans. Tricuspid valves guard the opening between right, , atrium and right ventricle. Bicuspid or mitral valve, guard the opening between left atrium and left, ventricle., , (v) How does the opening and closing of valves is, associated with the production of heart sound?, Ans. The first heart sound ‘lubb’ is associated with the, , closure of tricuspid and bicuspid valves. The second, heart sound ‘Dupp’ is associated with the closure of, semilunar valves (at the base of right and left ventricles)., , 2. Observe the given diagrametic representation of, formed elements of blood and answer the, following questions., , B, , A, , D, , E, , C, , F, , G, , H, , (i) Name the category of blood cells to which A and, H belong?, Ans. A is neutrophils and H is monocytes. Both neutrophils, , and monocytes belongs to the group of colourless,, nucleated cells called white blood cells. Neutrophils are, granulocytes and monocytes are agranulocytes., , (ii) How does A appears under the microscope?, Ans. Neutrophils appear as rounded cells containing, , multilobed nucleus and granulated cytoplasm., , (iii) Mention the shape and function of H., Ans. Monocytes are rounded cells containing kidney shaped, , nucleus and cytoplasm without granules. These cells are, phagocytic in function., , (iv) Among the given formed elements of blood which, of the following constitue 2-3% of blood volume., Ans. C- Eosinophils constitute 2-3% of blood volume. They, , appear as rounded cells containing bilobed nucleus and, granulated cytoplasm in a blood smear., , (v) What is the approximate number of erythrocytes,, leucocytes and thrombocytes in human blood?, Ans. Approximate number of erythrocytes is, , 5-5.5 millions mm −3 , leucocytes is 6000 – 8000 mm −3 ,, thrombocytes is 1,500,00 – 3,500, 00 mm −3 .

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Chapter Test, , Assertion-Reasoning MCQs, Direction (Q. Nos. 1-3) Each of these questions, contains two statements, Assertion (A) and Reason, (R). Each of these questions also has four alternative, choices, any one of which is the correct answer. You, have to select one of the codes (a), (b), (c) and (d), given below., , Multiple Choice Questions, , 1. Find the correct descending order of percentage, proportion of leucocytes in human blood, (a) Neutrophils → Basophils → Lymphocytes → Acidophils, (Eosinophils) → Monocytes, (b) Monocytes → Neutrophils → Lymphocytes → Acidophils →, Basophils, (c) Neutrophils → Lymphocytes → Monocytes → Acidophils →, Basophils, (d) Lymphocytes → Acidophils → Basophils → Neutrophils →, Monocytes, , 2. Artificial pacemaker is grafted at the place of, (a), (b), (c), (d), , superior to the four-chambered heart of crocodiles., Reason (R) In this system, the oxygenated and, deoxygenated blood are completely separated., closed during ventricular systole., Reason (R) These valves in heart allow blood to flow, in one direction and prevent backward flow., , 3. Which one of the following blood cells is involved in, antibody production?, , 3. Assertion (A) The body has the ability to alter the, stroke volume and the heart rate., Reason (R) The metabolic needs of the body are, met by these changes, but the duration of cardiac, cycle remains same., , (a) B-lymphocytes, (b) T-lymphocytes, (c) RBC, (d) Neutrophils, , 4. The opening and closing of semilunar valves depend upon, (a) increased and decreased pressure in ventricles, (b) atrial systole, (c) duration of nerve impulse to travel through atria and ventricles, (d) amount of blood presents in left ventricle, , Short Answer Type Questions, , 1. What is erythroblastosis foetalis or haemolytic, diseases of the newborn?, , 2. What is meant by single circulation? Give an, example., , 3. Describe incomplete double circulation with an, , 5. Systemic circulation is, Left, ventricle, Left, (b), ventricle, , 1. Assertion (A) The four-chambered heart of birds is, , 2. Assertion (A) Bicuspid and tricuspid valves get, , atrio-ventricular bundle, Purkinje fibre, sino-atrial node, atrio-ventricular node, , (a), , (a) Both A and R are true and R is the correct, explanation of A, (b) Both A and R are true, but R is not the correct, explanation of A, (c) A is true, but R is false, (d) A is false, but R is true, , example., , Deoxygenated, , Tissues, , blood, Oxygenated, , Tissues, , blood, , (c), , Left, ventricle, , Deoxygenated, , (d), , Left, ventricle, , Oxygenated, , blood, , Tissues, Tissues, , blood, , Oxygenated, blood, Deoxygenated, blood, Oxygenated, blood, Deoxygenated, blood, , Right, ventricle, Right, auricle, Right, auricle, Right, auricle, , 4. Describe the process of atrial systole., 5. Describe coronary circulation., Long Answer Type Questions, , 1. Describe briefly the conducting system of human, heart., , 2. Explain the process of double circulation in detail., , Answers, Multiple Choice Questions, 1. (c), , 2. (c), , 3. (a), , 4. (a), , Assertion-Reasoning MCQs, 1. (a), , 2. (a), , 3. (c), , 5. (d), , For Detailed Solutions, Scan the code

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115, , CBSE Term II Biology XI, , CHAPTER 07, , Excretory Products, and their Elimination, In this Chapter..., , l, , l, , l, , l, , l, , Excretory Organs, , l, , Role of Other Organs in Excretion, , l, , Human Excretory System, , l, , Disorders of Excretory System, , l, , Urine Formation, , l, , Artificial Kidney, , l, , Counter-Current Mechanism, , l, , Renal (Kidney) Transplantation, , l, , Regulation of Kidney Functions, , Excretion is defined as the process of eliminating waste products accumulated by metabolic activities or by excess, ingestion., The waste products constituting various types of nitrogenous compounds such as NH 3 , urea, uric acid, etc., are eliminated, by different organisms based on availability of water., Depending upon the types of excretory material, organisms are classified as ammonotelic, ureotelic and uricotelic., The various features and examples of the modes of excretion are tabulated below, Modes of Excretion Excreted Materials, , Examples, , Ammonotelism, , Ammonia is excreted by diffusion across body surface as, NH 3+ ions. Organisms require great amount of water as, ammonia is highly toxic. Kidneys are not involved in this., , Bony fishes, aquatic amphibians and aquatic, insects., , Ureotelism, , Urea is excreted through kidneys which is produced by the, conversion of ammonia in liver. Urea is less toxic than, ammonia and is less soluble in water. It can be retained in, body in small amount to maintain osmolarity., , Terrestrial animals, marine fishes., , Uricotelism, , Uric acid is excreted in the form of pellet or paste with, minimum loss of water. Uric acid crystals are non-toxic and, almost insoluble in water., , Reptiles, birds, land snails, insects.

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116, , CBSE Term II Biology XI, , Excretory Organs, Different animal groups have a variety of excretory structures (organs) to perform the process of excretion. In most of the, invertebrates, these structures are simple tubular form, whereas vertebrates have complex structured organs called kidneys., Some of these structures are mentioned below in the given table, Excretory Organs and Main Nitrogenous Wastes of Different Animal Groups, Animal Groups, , Excretory Organs, , Main Nitrogenous Wastes, , Protozoans (Amoeba), Poriferans (Sycon),, Coelenterates or Cnidaria (Hydra), , Plasma membrane, pellicle and general body surface, , Ammonia, , Ctenophora, , Anal pores, , Ammonia, , Platyhelminthes (flatworms), e.g. Planaria, Fasciola, Taenia, , Protonephridia with flame cells, , Ammonia, , Rotifers, , Flame cells, , Ammonia, , Nemathelminthes (Aschelminthes), e.g. roundworms, Ascaris, , Renette cells, , Ammonia and urea, , Annelida, , Metanephridia (in Nereis and leech), Metanephridia and, Chloragogen cells (in earthworm), , Ammonia and urea, , Arthropoda, , Malpighian tubules (in cockroaches), coxal gland, green glands Uric acid and ammonia, or antennary glands (in crustaceans), , Mollusca, , Renal gland or organ of Bojanus (in Pila and Unio) and Keber’s Ammonia in aquatic and uric, acid in larva forms, organ (in Unio), , Echinodermata, , Tubefeet (podia) and dermal branchiae (thin walls of gills), , Chordata, , Ammonia, urea and uric acid, Protonephridia (in Lancelets), neural gland (in Herdmania),, pharyngeal nephridia and Hatschek’s nephridium in, cephalochordates (Amphioxus). a pair of kidneys in vertebrates, , Ammonia, , Human Excretory System, , 1. Kidneys, , Human excretory system consists of a pair of kidneys, a pair, of ureters, a urinary bladder and urethra, these are described, below in detail, , These are reddish-brown, bean-shaped structures situated, between the levels of last thoracic and third lumbar vertebra., These are close to the dorsal inner wall of the abdominal, cavity., Each kidney of an adult human measures, 10-12 cm in length,, 5-7 cm in width, 2-3 cm in thickness with an average weight, of 120-170 gm (i.e. 150 gm in males and about 135 gm in, females)., Kidneys are mesodermal in origin. They develop from, mesodermal nephrostomes or mesomeres (ciliated structures,, functional in embryonic conditions)., , Adrenal gland, Inferior, vena cava, , Renal artery, , Pelvis, , Renal vein, , Medullary, pyramid, , Kidney, , Cortex, Dorsal aorta, Ureter, , Urinary bladder, Urethra, Human excretory system, , Position of Kidneys, The kidneys are located below the diaphragm on the left and, right sides. The right kidney is lower and smaller than the left, kidney because the liver takes up much space of the right, side., Structure of Kidneys, It can be studied well under two heads, i.e. external as well as, internal structure.

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117, , CBSE Term II Biology XI, , These are described below as, , from the blood and delivers small solutes to the renal, tubule for modification., , External Structure, l, , l, , l, , The outer surface of each kidney is convex. Inner concave, surface has a notch called hilum. The supply of blood occurs, through hilum, i.e. renal artery and renal vein, pass in and out, of the kidneys along with the ureter and the nerve supply of, kidney., If we look from outside to inside, three layers cover the, kidneys, i.e. renal fascia (outermost), the adipose layer and, then renal capsule (innermost layer)., These coverings protect the kidneys from external shocks and, injuries., , Efferent arteriole, Afferent, arteriole, , Glomerulus, , Proximal convoluted, tubule, , Malpighian body (renal corpuscle), , Internal Structure, l, , The LS of a mammalian kidney shows an outer cortex and, inner medulla., Renal column, , (a) Glomerulus It is a tuft of thin-walled capillaries, formed by the branching of afferent arteriole (a, fine branch of renal artery). The afferent arteriole, is short and wide that supplies blood to the, glomerulus, while the efferent arteriole is narrow, and long carrying blood away from the glomerulus., , Medullary pyramid, Calyx, , (b) Bowman’s Capsule (Glomerular capsule) It is a, double-walled, cup-like structure that surrounds, the glomerulus. The outer parietal wall of, glomerulus is composed of flattened (squamous), cells and the inner visceral wall is composed of a, special type of less flattened cells, called, podocytes., , Renal artery, Renal vein, , Cortex, , Renal pelvis, Renal capsule, , l, , l, , Each kidney is composed of numerous (nearly one million), complex tubular structure called nephrons. These are the, functional units of kidney., Each nephron consists of two parts, i.e. the Malpighian body or, renal corpuscle and the renal tubule., , i. Malpighian Body or Renal Corpuscle, Glomerulus along with Bowman’s capsule is called the, Malpighian body or renal corpuscle which filters out large solutes, , Henle's loop, , Microscopic Structure, , Afferent arteriole, , 123, , l, , Inside the kidney, the ureter is expanded as a funnel-shaped, cavity called pelvis. The free end of pelvis has number of, cup-like cavities are called major calyces (sing. calyx) and, minor calyces., Medulla projects into the calyces as conical processes, called, renal pyramids or medullary pyramids. The tip of pyramids, are called renal papillae. The cortex spreads in between, medullary pyramids as renal columns called columns of, Bertini., , Malpighian body, , Ureter, , LS of kidney, l, , Bowman’s capsule, , Glomerulus, ,, Bowman s, capsule, , Descending limb, of loop of Henle, , Efferent arteriole, , Neck, Proximal, Convoluted, Tubule (PCT), Distal, Convoluted, Tubule (DCT), , Ascending limb, of loop of Henle, Vasa recta, , Collecting duct, , Diagrammatic representation of a nephron, , ii. Renal Tubules, Attached to each Bowman’s capsule is a long, thin tubule, with three distinct regions.

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118, , CBSE Term II Biology XI, , These regions are described as follows, (a) Proximal Convoluted Tubule (PCT) Behind the, neck, it makes few coils and is restricted to the, cortical region of the kidney., (b) Henle’s Loop It is quite narrower and U-shaped or, hair pin-shaped having a descending limb that ends, into the medulla and an ascending limb that extends, back from the medulla into the cortex., Differences between Descending Limb, and Ascending Limb of Henle’s Loop, Descending Limb, , Ascending Limb, , It is very thin., , It is thick., , Direction of fluid flow is, downward., , Direction of fluid flow is, upward., , Permeable to water., , Impermeable to water., , (c) Distal Convoluted Tubule (DCT) is thicker and, highly coiled structure situated in the cortex like the, proximal tubule. Coils of both convoluted tubules are, intermingled., (d) Collecting Tubule The last part of nephron is called, collecting or straight tubule, which is lined by, cuboidal cells., Collecting tubules of many nephrons open into a, large collecting duct. Several adjacent collecting, tubules converge to open into a short and thick duct, of Bellini. All ducts of Bellini, then open into the, renal pelvis through medullary pyramids in the, calyces., Peritubular Capillary Network (PTCN) is formed when a, minute vessel of peritubular capillaries runs parallel to the, loop of Henle forming a U-shaped vasa recta., All these capillaries join to form renal venules, which join to, form a renal vein that opens into the inferior vena cava., , Functions of Kidney, Following functions are served by kidney, (i) Regulation of water and electrolyte balance., (ii) Regulation of arterial pressure., (iii) Excretion of metabolic waste and foreign chemicals., (iv) Secretion of hormones like renin., , 2. Ureters, The pelvis of each kidney is continued as a ureter and emerges, out at hilus. Ureter is a long and muscular tube. Ureters of, both sides extend posteriorly and open into the urinary, bladder., , 3. Urinary Bladder, It is a thin-walled, pear-shaped, white transparent sac present, in the pelvic cavity. It temporarily stores the urine., , 4. Urethra, It is a membranous tube, which conducts urine to the exterior., The urethral sphincters keep the urethra closed except during, voiding of urine., , Urine Formation, The formation of urine is the result of the processes like, glomerular filtration, reabsorption and secretion. These, processes occur in different parts of nephrons. Details of these, are as follows, , 1. Glomerular Filtration, l, , l, , Types of Nephrons, Based on the location in the kidney, nephrons are of, following two types, i. Cortical Nephrons, In majority of nephrons, the loop of Henle is too short and, extends only very little into the medulla, i.e. lie in the renal, cortex. Such nephrons are called cortical nephrons., ii. Juxtamedullary Nephrons, In some of the nephrons, the loop of Henle is very long and, runs deep into the medulla. These nephrons are called, juxtamedullary nephrons., Note The cortical nephron forms about 80% of the total nephron, count while rest 20% are the juxtamedullary nephron., , l, , The first step of urine formation is the filtration of blood. It, is carried out by the glomerulus. That is why this step is, called glomerular filtration., Kidneys filter about 1100-1200 mL of blood per minute,, which constitute roughly 1/5th of the blood pumped out by, each ventricle of the heart in a minute., The glomerular capillary blood pressure causes filtration of, blood through three layers, i.e., (i) the endothelium of glomerular blood vessels., (ii) the epithelium of Bowman’s capsule., , l, , l, , (iii) a basement membrane (present between the above, mentioned two layers)., The podocytes (epithelial cells of Bowman’s capsule) are, arranged in such a manner, so that some minute spaces, called filtration slits or slit pores occur between them., On account of the high pressure in the glomerular, capillaries, the substances are filtered through these pores

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119, , CBSE Term II Biology XI, , into the lumen of the Bowman’s capsule (but the RBC,, WBC and plasma proteins having high molecular weight, are unable to pass out)., That is why, this process of filtration through glomerular, capillaries in the Bowman’s capsule is known as, ultrafiltration and the filtrate is called glomerular filtrate., It is hypotonic to urine that is actually excreted., Basic function of nephron is to clear out the plasma from, unwanted substrates and also maintain the osmotic, concentration of the blood plasma. Thus, the fluid coming out, is known as urine, whose formation occurs inside the kidney., , l, , l, , 3. Tubular Secretion, It is also an important step in urine formation. Certain, chemicals in the blood that are not removed by filtration from, the glomerular capillaries are removed by this process of, tubular secretion. It helps in the maintenance of ionic and, acid-base balance of body fluids by removing chemicals like, foreign bodies, ions (K + , H + , NH+4 ) and molecules, (medicines), etc., that are toxic at elevated levels., Differences between Tubular Reabsorption and Tubular, Secretion, , Glomerular Filtration Rate, l, , The amount of the filtrate formed by the kidneys per minute is, called Glomerular Filtration Rate (GFR). In a healthy person,, it was found approximately 125 mL /min,, i.e. 180 L/day., , l, , GFR is regulated by one of the efficient mechanism carried out by, Juxtaglomerular Apparatus (JGA)., , l, , JGA is a special sensitive region formed by cellular modifications, in the distal convoluted tubule and the afferent arteriole at the, location of their contact., , l, , This apparatus includes, (i) granular juxtaglomerular cells in the afferent arteriole., (ii) macula Densa cells of DCT., (iii) agranular lacis cells situated in between the above two., , l, , A fall in GFR can activate the JG cells to release renin, which can, stimulate the glomerular blood flow and thereby, the GFR back to, normal., , 2. Selective Reabsorption, , l, , This is the second step in the formation of urine from, filtrate. The urine released is 1.5 L as compared to the, volume of the filtrate formed per day (180 L). It suggests, that as much as 99% of the material in the filtrate is, reabsorbed by the renal tubules. Thus, the process is called, reabsorption., Depending upon the types of molecules being reabsorbed,, movements into and out of epithelial cells in different, segments of nephron occur either by passive transport or, active transport., , These are described as follows, (i) Water and urea are reabsorbed by passive transport, (i.e. water is reabsorbed by osmosis and urea by simple, diffusion)., (ii) Glucose and amino acids are reabsorbed by active, transport., (iii) The reabsorption of Na + occurs both by passive and, active transport., , Tubular Secretion, , It involves the absorption of, water and useful solutes from, the glomerular filtrate into the, blood., , It refers to the passage of waste, materials from blood into the, filtrate or nephrons., , It occurs by back diffusion and, active transport., , It takes place only by active, transport., , It occurs mostly in PCT., , It occurs mostly in DCT., , It does not occur in animals, It is the only mode of excretion, that lack glomerulus (e.g., in animals that lack glomerulus., marine fish and desert animals)., , Functions of the Tubules, When the glomerular filtrate/primary urine passes through, renal tubule, water and different materials of filtrate reabsorb, at various places., These are given below in the following manner, i. Proximal Convoluted Tubule (PCT), l, , l, , Tubular Reabsorption, , l, , l, , The epithelial cells of the PCT have numerous microvilli, (simple cuboidal brush-border epithelium) which increase, the surface area available for reabsorption., The process of reabsorption mostly (65%) takes place, within PCT (i.e. nearly all of the essential nutrients, 70-80%, of electrolytes and water). PCT also helps in the absorption, of HCO −3 from the filtrate., Selective secretion of hydrogen ions, ammonia and, potassium ions takes place here to maintain the pH and, ionic balance of the body fluids. The filtrate is considered, isotonic to blood plasma., , ii. Henle’s Loop, Reabsorption in Henle’s loop is minimum, besides this, it plays, an important role in maintaining the high osmolarity of, medullary interstitial fluid. Two portions of Henle’s loop, play, different role in osmoregulation. These are as follows, (a) Descending Limb of Loop of Henle Water is reabsorbed, here due to increasing osmolarity of interstitial fluid, but

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120, , CBSE Term II Biology XI, , sodium and other electrolytes are not reabsorbed here., This concentrates the filtrate as it moves down., (b) Ascending Limb of Loop of Henle This segment is, impermeable to water, but permeable to K + , Cl – and, Na + and partially permeable to urea. Thus, in the thick, ascending limb of the loop of Henle, Na + , K + , Mg 2 +, and Cl – are reabsorbed. Therefore, as the concentrated, filtrate pass upward, it gets diluted due to the passing, out of electrolytes to the medullary fluid of kidney., iii. Distal Convoluted Tubule (DCT), Active reabsorption of sodium ions from the filtrate takes, place under the influence of aldosterone., Water is also reabsorbed here. With associated secretion of, potassium (K + ), hydrogen (H + ) ions, NH 3 , some Cl –, (chloride) ions and HCO –3 are also reabsorbed here. It is, necessary to maintain the pH and sodium-potassium balance, in blood. This makes the filtrate isotonic to blood plasma., Proximal convoluted tubule, NaCl Nutrients, , –, HCO3, , +, , K, , H 2O, , NH3, , +, , K, , HCO3, , +, , H, , l, , l, , H 2O, , Collecting duct, Thin segment of, ascending limb, , Kidney of higher vertebrates (such as mammals, birds and, man) has the ability of absorbing more and more water from, tubular filtrate to conserve water and make the urine more, concentrated., This can be achieved by a special mechanism known as, counter-current mechanism. The basic concept and, mechanism of this mechanism are as follows, , NaCl, Urea, , l, , The composition of body fluids is influenced more by the, output through the kidneys than by the intake via the gut., Therefore, the kidneys are important guardians of the, internal environment., By means of the regulated production of urine from the, blood the nephrons carryout the dual process of excretion, and osmoregulation., The two types of nephrons, differing both in their position, in the kidney and in the length of the loop of Henle, play, an important role in osmoregulation., Cortical nephrons function most importantly when the, water supply is normal to excessive. Juxtamedullary, nephrons work when water is in short supply., , Counter-Current Mechanism, , NaCl, , Medulla, , Osmoregulation, , l, , Thick segment of, ascending limb, , CT (Collecting Tubule) allows passage of small amounts of, urea into the medullary interstitial tissue to maintain the, osmolarity. It also plays an important role in the, maintenance of pH and ionic balance of the blood by the, selective secretion of H + and K + ions., Therefore, the filtrate is now becomes urine. Thus, urine is, isotonic to medullary fluid and hypertonic to blood., , Note Concentrations of important ions and other substances in the, blood are controlled by regulating levels of water in the blood., , –, , H2 O, , NaCl, , Cortex, , Descending, limb of loop of, Henle, , l, , Distal convoluted tubule, , +, , H, , l, , H2 O, , Basic Concept, Reabsorption and secretion of major substances at different parts, of the nephron (arrows indicate direction of movement of, , materials), , iv. Collecting Duct, l, , l, , This duct extends from the cortex of the kidney to the inner, parts of the medulla and is highly permeable to water., Thus, a considerable amount of water is reabsorbed here, under the influence of ADH to produce concentrated, filtrate., Sodium ions are also reabsorbed here as release of, aldosterone increases the permeability of wall of DCT for, sodium ions., , (i) Henle’s loop and vasa recta (capillary loop) play an, important role in this mechanism. The flow of filtrate, in the limbs of Henle’s loop is in opposite directions, and thus, forms a counter-current. The flow of blood, within the two limbs of vasa recta also occurs in the, counter-current pattern., (ii) The osmolarity (i.e. number of Osmols of solute per, litre) of renal cortical interstitium is the same, (300 mOsmolL) as in other tissues, but that of the, interstitium of renal medulla is hypertonic with a, gradient of hyperosmolarity from renal cortex to the, tips of medullary papillae., The hyperosmolarity of medullary interstitium near the, tips of the papillae is as high as 1200-1450 mOsmolL.

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121, , CBSE Term II Biology XI, , The Mechanism, l, , l, , l, , l, , l, , The gradient of increasing hyperosmolarity of medullary, interstitium is maintained by a counter-current mechanism and the, proximity between the Henle’s loop and vasa recta., This gradient is mainly caused by the to and fro movements of NaCl, and urea. The transport of these substances is facilitated by the, special arrangement of Henle’s loop and vasa recta., There are two aspects of this mechanism, (i) Counter-current multiplication (by the Henle’s loop)., (ii) Counter-current exchange (by the vasa recta)., NaCl is transported out by the ascending limb of Henle’s loop., These enter in the descending limb of vasa recta., , Regulation of Kidney, Functions, l, , Bowman’s capsule, , Afferent arteriole, , Glomerulus, H2O, NaCl, , Efferent arteriole, , 300, 300, , 300, , NaCl, 400, , NaCl, , NaCl, NaCl, , H2O, , 600, , 600, , 800, , 400, , NaCl, , H2O, , 900 mOsmolL–1, , H2O, , 400, , 600, , H2O, , H2O, , 800, 900, , 1000, , 1200 mOsmolL–1, , 800, 1000, , 1200, , Vasa recta, , l, , NaCl, 600, , NaCl, , Outer medulla, , NaCl, , NaCl, , 600 mOsmolL–1, , H2O, Urea, , 1000, 1200, , H2 O, , Nephron, , Urine, , Diagrammatic representation of a nephron and, vasa recta showing counter-current mechanism, l, , l, , l, , l, , 300, , 400, , Inner medulla, , 300 mOsmolL–1, , Cortex, , 200, , NaCl is returned to the medullary interstitium by the ascending, part of vasa recta. But contrarily, the water diffuses into the blood, of ascending limb of vasa recta and is carried away into the general, blood circulation., Permeability to urea is found only in the deeper parts of thin, ascending limb of Henle’s loop and collecting ducts., Urea diffuses out of the collecting ducts and enters into the thin, ascending limb. A certain amount of urea recycled and in this way it, is trapped in medullary interstitium by the collecting tubule., Thus, collecting tubule also plays a minor role in the process (as, shown in the figure above)., , The counter-current mechanism helps in the, maintenance of a concentration gradient in the, medullary interstitium., Presence of such gradient helps in an easy passage, of water from the collecting tubule resulting in the, formation of concentrated urine (filtrate), i.e., nearly four times concentrated than the initial, filtrate formed., , To maintain homeostasis, the regulation of water, and solute contents of the body fluids is performed, by the kidneys. The vertebrate kidney is very, flexible in its functioning. It excretes larger, quantities of dilute urine when water is abundant, in the body tissues and small amounts of, concentrated urine when there is shortage of, water., Hormones act as an important signalling, molecules in controlling the regulation of water, content in blood with the help of kidneys. The, functioning of the kidneys is efficiently monitored, and regulated by hormonal feedback mechanism, involving hypothalamus, JGA (Juxtaglomerular, Apparatus) and to a certain extent, the heart., Regulation of the functioning of kidneys can be, discussed under the following headings, , Regulation by the Hypothalamus, Excessive loss of fluid from the body activates, osmoreceptors present in blood vessels of, hypothalamus, thus stimulating it to release ADH or, vasopressin from the neurohypophysis. ADH release, increases water reabsorption from DCT. An increase, in body fluid volume switches off the osmoreceptors, and suppresses the ADH release to complete the, feedback. ADH also causes constrictory effects on, blood vessels of glomerulus thus, increasing pressure, for faster filtration., , Regulation by the Juxtaglomerular, Apparatus (JGA), As blood pressure/glomerular blood flow /GFR, decreases, the cells of the JGA release the enzyme, renin., Renin converts angiotensinogen in blood to, Angiotensin-I and Angiotensin-II (active form). This, mechanism is generally known as the, Renin-angiotensin mechanism.

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122, Angiotensin has following effects, (i) Raises blood pressure by constricting blood vessels (being, a powerful vasoconstrictor) and thereby, GFR., (ii) Activates the adrenal cortex to release aldosterone., (iii) Aldosterone causes reabsorption of Na + and water from, the distal parts of the tubule. This also leads to an, increase in blood pressure and GFR., , Regulation by the Heart, Atrial Natriuretic Factor (ANF) is produced by the atria of, heart when blood volume decreases. This causes vasodilation, (dilation of blood vessels) and thereby, decreases the blood, pressure., ANF also inhibits Na + and Cl − ions reabsorption in DCT and, increases concentration of urine., , Urine, An adult man normally passes about 1-1.5 L of urine per day., Composition Urine normally contains, water 95%, salts 2%,, urea 2.6%, uric acid 0.3%, traces of creatinine, creatine,, ammonia, etc., Colour Pale yellow, due to pigment urochrome produced by, the breakdown of haemoglobin., pH Ranges from 4.5-8.2, average pH 6.0 (i.e. slightly acidic)., Odour Unpleasant, if allowed to stand imparts strong smell, like, ammonia., Least concentration of urea is found in renal vein because urea, is excreted through urine formed in kidney. On an average,, 25-30 g of urea is excreted out per day. Highest concentration, of urine is found in hepatic vein because urea is synthesised in, liver., Analysis of urine helps in clinical diagnosis of many metabolic, disorders as well as malfunctioning of the kidney., For example, presence of glucose (glycosuria) and ketone, bodies (ketonuria) in urine are indicative of diabetes mellitus, and presence of protein, blood and pus in the urine is called, proteinuria, haematuria and pyuria, respectively., , Role of Other Organs in, Excretion, Other than the kidneys, there are some accessory excretory, organs also that help in the elimination of excretory wastes., These are described as follows, , 1. Lungs, Carbon dioxide and water are the waste products formed in, respiration. Lungs remove the CO 2 and some water as vapour, in the expired air. About 18 L of CO 2 per hour and 400 mL of, water per day are eliminated by human lungs., , CBSE Term II Biology XI, , 2. Liver, It changes the decomposed haemoglobin of the wornout, red blood corpuscles into bile pigments, i.e. bilirubin and, biliverdin. These pigments pass into the alimentary canal, with the bile for elimination in the faeces. The liver also, excretes cholesterol, steroid hormones, certain vitamins, and drugs via bile., Liver deaminates the excess and unwanted amino acids,, producing ammonia, which is quickly combined with CO 2, to form urea in urea cycle or Ornithine cycle, which is, further removed by the kidneys., , 3. Skin, The sweat glands and sebaceous glands in the skin can, eliminate certain substances through their secretions., (i) Sweat Glands The secretion of sweat glands (sweat), is an aqueous fluid containing NaCl, lactic acid,, small amounts of urea, amino acids and glucose., Control of sweat lost is an example of homeostasis, control, for regulating the body temperature (i.e. to, facilitate a cooling effect on the body surface)., (ii) Sebaceous Glands Sebum from sebaceous glands, eliminates sterols, fatty acids, waxes and, hydrocarbons. This secretion is mainly meant for, protective oily covering of the skin., , 4. Intestine, Epithelial cells of colon excrete excess salts of calcium,, magnesium and iron along with faeces., , 5. Salivary Glands, Heavy metals and drugs are excreted in the saliva., , Disorders of the Excretory, System, Malfunctioning of kidneys can lead to several disorders of, the excretory system., Some of these are as follows, (i) Uremia It is the presence of an excessive amount of, urea in the blood. Urea is highly harmful as it, poisons the cells at high concentration and may lead, to kidney failure., (ii) Kidney Failure (renal failure) Partial or total, inability of kidneys to carry on excretory and, salt-water regulatory functions is called renal or, kidney failure., (iii) Renal Calculi It is the formation of stone or, insoluble mass of crystallised salts (calcium,, magnesium, phosphates and oxalates, etc.), formed, within the kidney.

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123, , CBSE Term II Biology XI, , (iv) Glomerulonephritis It is the inflammation of glomeruli, of kidney., (v) Diabetes Insipidus (DI) It is a condition characterised, by excessive thirst and frequent micturition., The urine excreted is severely diluted. There are several, different types of DI, each with a different cause. The, most common type in human is central DI, caused by the, deficiency of Arginine Vasopressin (AVP), also known as, Anti Diuretic Hormone (ADH). The second common, type of DI is nephrogenic diabetes insipidus, which is, caused by an insensitivity of the kidney to ADH., , Artificial Kidney (Haemodialyser), Artificial kidney is a machine that is used to filter the blood (to, remove urea and other nitrogenous wastes) of a person, whose, kidneys are damaged., The process is called haemodialysis., The outline details of apparatus and the process are as follows, (i) It works on the principle of dialysis (i.e. diffusion of, small solute molecules through a semipermeable, membrane (cellophane)., (ii) Blood of the patient is pumped from one of the arteries, into the dialysing unit (haemodialyser) after cooling it to, 0°C and mixing with an anticoagulant (heparin)., (iii) Haemodialyser is a cellophane tube suspended in a, dialysing fluid (salt-water solution) of the same, , composition as that of plasma except the, nitrogenous wastes (urea)., (iv) Pores of the cellophane tube allow the passage of, molecules based on concentration gradient., Nitrogenous wastes like urea, uric acid, creatinine,, excess salts and excess H + ions easily get diffuse, from the blood into the surrounding solution. Thus,, the blood is cleared of nitrogenous waste products, without losing plasma proteins., (v) The blood thus purified, is warmed to body, temperature, checked to ensure that it is isotonic to, the patients blood. Now, the blood is mixed with an, anti-heparin to restore its normal clotting power, and then pumped back to the body of patient, through a vein, usually the radial vein., , Renal (Kidney) Transplantation, Grafting a kidney from a compatible donor to restore, kidney functions in a recipient suffering from kidney, failure is called renal or kidney transplantation. It is an, ultimate method in the correction of acute renal failures., A living donor can be used in a kidney transplant. It may, be an identical twin, a sibling or a close relative to, minimise the chances of rejection by the immune system, of the host. To prevent the rejection of transplanted, kidney, special drugs are also used, which suppress the, recipients immune system.

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124, , CBSE Term II Biology XI, , Chapter, Practice, PART 1, Objective Questions, l, , Multiple Choice Questions, 1. Which of the following structures help in the, removal of nitrogenous waste as well as concerned, with osmoregulation?, , (a) Protonephridia, (c) Malpighian tubules, Ans. (d) Option (d) is correct., , (b) Nephridia, (d) All of the above, , 2. Part of the kidney through which the ureter, blood, vessels and nerves enter into it is, (a) renal cortex, (b) renal medulla, (c) hilum, (d) urethra, Ans. (c) Hilum is a notch towards the centre of the inner, concave surface of the kidney through which the ureter,, blood vessels and nerves enter into the kidneys., , 3. Which of the following is a part of medullary, pyramid?, (a) Proximal convoluted tubule, (b) Distal convoluted tubule, (c) Malpighian corpuscle, (d) Loop of Henle, Ans. (d) Loop of Henle is a part of medullary pyramid. The, Malpighian corpuscle, PCT and DCT of the nephron are, situated in the cortical region of the kidney whereas the, loop of Henle dips into the medulla., , 4. What is the function of Bowman’s capsule and, glomerulus?, (a) Filtration of blood, (b) Reabsorption of ions from blood, (c) Reabsorption of hormones from blood, (d) Reabsorption of water from blood, Ans. (a) The function of Bowman’s capsule and glomerulus is to, perform filtration of blood through a mechanism known as, glomerular filtration or ultrafiltration. Reabsorption of, ions, hormones and water does not take place in it., , 5. Match the following parts of a nephron with their, function., Column I, (Parts of Nephron), , Column II, (Functions), , A. Descending limb of, , 1. Reabsorption of salts only, , B. Proximal convoluted, , 2. Reabsorption of water only, , C. Ascending limb of, , 3. Conditional reabsorption, , D. Distal convoluted, , 4. Reabsorption of ion, water, , Henle’s loop, tubule, , Henle’s loop, tubule, , of sodium ion and water, and organic nutrients, , Codes, A B C D, (a) 1 3 2 4, (b) 2 4 1 3, (c) 1 4 2 3, (d) 4 1 3 2, Ans. (b) A–2, B–4, C–1, D–3, , 6. Which part of excretory system store the urine?, (a) Kidney, (b) Ureters, (c) Urethra, (d) Urinary bladder, Ans. (d) Urinary bladder temporarily stores the urine., , 7. The portion of a nephron which is relatively, impermeable to water is, (a) collecting tubule, (b) ascending limb of Henle, (c) distal convoluted tubule, (d) descending limb of Henle, Ans. (b) The portion of a nephron which is impermeable to, water is the ascending limb of Henle. However, it allows, transfer of electrolytes actively or passively.

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125, , CBSE Term II Biology XI, , 8. Ultrafiltrate formed by the glomerulus contains all, , 13. Osmolarity in the cortex and inner medulla, respectively are, , the constituents of the blood plasma except, (a) protein, (b) minerals, (c) urea, (d) All of these, Ans. (a) Protein is not present in ultrafiltrate. Blood is filtered, so finely in glomerulus that almost all the constituents of, the plasma, except the proteins, pass into the lumen of, the Bowman’s capsule. This process is called, ultrafiltration and the filtrate is known as ultrafiltrate., , (a) 300 m Osmol L–1, 1200 m Osmol L–1, (b) 200 m Osmol L–1, 1300 m Osmol L–1, (c) 1200 m Osmol L–1, 300 m Osmol L–1, (d) None of the above, Ans. (a) An increasing osmolarity towards the inner medullary, interstitium is maintained, from 300 m Osmol L–1 in cortex, to 1200 m Osmol L–1 in the inner medulla of kidney., , 9. The human urine is usually acidic because, (a) the sodium transporter exchanges one hydrogen ion, for each sodium ion in peritubular capillaries, (b) excreted plasma proteins are acidic, (c) potassium and sodium exchange generates acidity, (d) hydrogen ions are actively secreted into the filtrate, Ans. (d) Active secretion of H + ions into the filtrate occurs in, the PCT, DCT and collecting duct of renal tubule. High, concentration of H + ions decreases the pH of filtrate and, thus, the urine becomes acidic., , 10. Choose the mismatched part of nephron with its, , 14. The principal nitrogenous excretory compound in, humans is synthesised, (a) in kidneys, but eliminated mostly through liver, (b) in kidneys as well as eliminated by kidneys, (c) in liver and also eliminated by the same through bile, (d) in the liver, but eliminated mostly through kidneys, Ans. (d) The principal nitrogenous excretory compound in, humans is urea. It is synthesised in the mitochondrial, matrix and cytosol of liver cells and eliminated through, kidneys., , 15. Match the following columns., , function., (a) Bowman’s capsule–Glomerular filtration, (b) PCT–Reabsorption of Na + and K +, (c) DCT–Reabsorption of glucose, (d) Loop of Henle–Urine concentration, Ans. (c) Option (c) contains the mismatched pair. It can be, corrected as, Distal Convoluted Tubule (DCT) performs conditional, reabsorption of Na + and water., Rest of the matches are correct., , 11. Which among the following releases renin in, response to low GFR?, (a) Hypothalamus, (b) Anterior lobe of pituitary, (c) Posterior lobe of pituitary, (d) JG cells, Ans. (d) A fall in GFR activates JG cells to release renin which, stimulates glomerular blood flow and brings GFR back to, normal., , 12. Angiotensin-II increases the glomerular blood, pressure and GFR as it is a/an, (a) osmoregulator, (b) vasoconstrictor, (c) vasodilator, (d) None of the above, Ans. (b) Angiotensin-II, being a powerful vasoconstrictor,, increases the glomerular blood pressure and thereby, GFR. Angiotensin-II also activates the adrenal cortex to, release aldosterone., , Column I, (Disorders), A. Glomerulonephritis, , 1., , Excess of protein level in, urine., , B. Ketonuria, , 2., , The presence of high ketone, bodies in urine., , C. Glycosuria, , 3., , Inflammation of glomeruli, , D. Proteinuria, , 4., , The presence of glucose in, urine., , Codes, A B C D, (a) 3 2 4 1, (c) 3 4 2 1, Ans. (a) A–3, B–2, C–4, D–1, l, , Column II, (Features), , A B C D, (b) 4 3 2 1, (d) 3 2 1 4, , Assertion-Reasoning MCQs, Direction (Q. Nos. 1-5) Each of these questions, contains two statements, Assertion (A) and Reason, (R). Each of these questions also has four alternative, choices, any one of which is the correct answer. You, have to select one of the codes (a), (b), (c) and (d), given below., (a) Both A and R are true and R is the correct explanation, of A, (b) Both A and R are true, but R is not the correct, explanation of A, (c) A is true, but R is false, (d) A is false, but R is true

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126, , CBSE Term II Biology XI, , system., Reason (R) It is helpful in collection of urine., Ans. (c) A is true, but R is false because, , 2. Assertion (A) Conditional reabsorption of Na + and, , Case Based MCQ, 1. Observe the given diagram of a nephron and, answer the questions that follows., C, , B, 123, , Hilum is a notch present on the concave surface of the, kidneys through which ureter, blood vessels and nerves, enter into the kidneys. It is not concerned with collection, of urine. Urine is stored in the urinary bladder., , l, , Malpighian body, , 1. Assertion (A) Hilum is a part of human excretory, , A, ,, Bowman s, capsule, , water takes place in Distal Convoluted Tubule, (DCT)., Reason (R) The DCT allows passive absorption of, Na + and active absorption of Cl − along with water., , D, , Ans. (c) A is true, but R is false because, , In DCT, conditional reabsorption of Na + and water, occurs. Here, Na + is reabsorbed actively, while Cl − ions, are reabsorbed passively along with H 2O., , 3. Assertion (A) RAAS gets activated in a person, suffering from diarrhoea., Reason (R) Both loss of water and electrolytes takes, place in such a patient., Ans. (a) Both A and R are true and R is the correct explanation, , of A., The person suffering from diarrhoea losses water and, electrolytes excessively from the body which results in, decreased blood pressure. This can be fatal for the, person. Thus, inorder to increase the blood pressure,, Renin-Angiotensin Aldosterone System (RAAS) gets, activated in the body., , 4. Assertion (A) Haemodialysis is used to clean the, excretory products generated from the blood., Reason (R) Dialysing fluid has same composition as, that of plasma except nitrogenous wastes., Ans. (b) Both A and R are true, but R is not the correct, , explanation of A., Haemodialysis is a process in which blood is purified, artificially if the kidneys fail to do their designated, function. The dialysing fluid used in haemodialysis has, same composition as that of plasma, but it does not, contain nitrogenous waste. Therefore, these wastes can, freely pass from blood into dialysing fluid, thus clearing, blood., , 5. Assertion (A) Dialytic fluid/solution is iso-osmotic, to blood plasma., Reason (R) The fluid used during dialysis, procedure contain glucose and ions., Ans. (d) A is false, but R is true because, , Fluid used in dialysis has similar composition to blood, plasma except for the presence of proteins and urea., Thus, it is not iso-osmotic., , (i) Identify the correct pair., (a) A–Blood flowing in it is poor in waste products, (b) B–Fine branches of renal vein, (c) C–Supply blood to glomerulus, (d) D–Highly coiled structure, Ans. (d) Option (d) is correctly paired. D represents Distal, Convoluted Tubule (DCT). It is thick and highly coiled, and is situated in the cortex like proximal tubule., Options (a), (b) and (c) are incorrectly matched pairs and, can be corrected as, A is glomerulus. It is a fine tuft of capillaries formed by, afferent arterioles., B is afferent arteriole. It brings arterial blood rich in, nitrogenous waste to renal corpuscle., C is efferent arteriole. It carries venous blood, poor in, nitrogenous waste away from the renal corpuscle., , (ii) Renal corpuscle constitutes, (a) glomerulus and Malpighian body, (b) glomerulus and Bowman’s capsule, (c) Bowman’s capsule and Malpighian body, (d) glomerulus only, Ans. (b) Renal corpuscle or Malpighian body constitutes, glomerulus and Bowman’s capsule together., , (iii) Which of the following structures are present in the, cortical region of the kidney?, I. PCT, II. DCT, III. Collecting duct, IV. Loop of Henle, Codes, (a) Only I, (c) I, II and III, , (b) I and II, (d) III and IV

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127, , CBSE Term II Biology XI, , Ans. (b) Proximal Convoluted Tubule (PCT) and Distal, , Convoluted Tubule (DCT) are situated in the cortical, region of the kidney whereas collecting duct and loop of, Henle dip into the medullary region., , (iv) What is the net glomerular filtration rate in an, average adult?, (a) 75 mL min −1, (b) 50 mL min −1, (c) 125 mL min −1, (d) 100 mL min −1, Ans. (c) In a healthy adult, the amount of filtrate formed by the, kidneys per minute, i.e. GFR is 125 mL min −1., , (v) Which of the following is incorrect with regard to, nephron?, (a) They are the structural and functional units of kidney, (b) Cortical nephrons have shorter loop of Henle whereas, juxtamedullary nephrons have longer loop of Henle, (c) A human kidney contains about two million nephrons, (d) DCT opens up into the collecting duct, Ans. (c) Statement in option (c) is incorrect and can be, corrected as, The number of nephrons in a human kidney is 1 million., Rest of the statements are correct., , PART 2, Subjective Questions, l, , Short Answer (SA) Type Questions, 1. Give the name of the three common nitrogenous, waste materials in vertebrates. Which of these is, most toxic and which one is least toxic?, , Ans. Nitrogenous waste materials in vertebrates occur as, , ammonia, urea and uric acid. Ammonia is most toxic,, while uric acid is least toxic., , 2. What is ureotelism? Describe the process of, formation of urea., Ans. The process of excreting urea is called ureotelism., , Animals, which do not live in high abundance of water, convert toxic ammonia produced in the body into urea by, the liver and then release it into the blood. This in turn is, filtered and excreted out by the kidneys., , 3. (i) Name the excretory organs found in, Aschelminthes and leeches., (ii) Name the arterioles through which blood enters, and leaves the glomerulus., (iii) Name the vessel of peritubular capillaries that, runs parallel to the loop of Henle., Ans., , (i) Renette cells and metanephridia are the excretory, organs found in Aschelminthes and leeches,, respectively., (ii) Through afferent arteriole and efferent arteriole, blood enters and leaves the glomerulus., (iii) Vasa recta runs parallel to the loop of Henle., , 4. Terrestrial animals are generally either ureotelic or, uricotelic, not ammonotelic, why?, (NCERT), Ans. Terrestrial adaptation requires the production of less toxic, nitrogenous wastes like urea and uric acid for the, conservation of water. Aquatic animals excrete ammonia, , which requires large amount of water to dissolve. The, huge quantity of water is easily available to such animals, from surroundings., However, for terrestrial animals, such a huge quantity of, water is not available, hence they modify NH 3 to, comparatively less toxic products like urea and uric acid, which require less amount of water for their excretion., , 5. Aquatic animals generally are ammonotelic in, nature, whereas terrestrial forms are not. Comment., Ans. Many bony fishes, aquatic amphibians and aquatic insects, , are ammonotelic in nature. Ammonia, as it is readily, soluble, is generally, excreted by diffusion across body, surfaces or through gill surfaces (in fish) as ammonium, ions., Terrestrial animals produce lesser toxic nitrogenous, wastes like urea and uric acid for conservation of water., Mammals, many terrestrial amphibians and marine fishes, mainly excrete urea and are called ureotelic animals., Ammonia produced by metabolism is converted into urea, in the liver of these animals and released into the blood, which is filtrated and excreted out by the kidneys. Some, amount of urea may be retained in the kidney matrix of, some of these animals to maintain a desired osmolarity., , 6. Name the two components of nephron that together, form Malpighian body or renal corpuscle., Ans. Glomerulus and Bowman’s capsule together constitute, , the Malpighian body., , 7. What are the two main types of nephrons?, Ans. Cortical nephrons and juxtamedullary nephrons are two, , main types of nephrons.

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128, , CBSE Term II Biology XI, , 8. Give the name of the excretory organ present in the, following animals., (i) Rotifers, (iii) Lancelets, Ans., , (i), (ii), (iii), (iv), , Rotifers, Cockroaches, Lancelets, Amphioxus, , 15. Indicate whether the following statements are true, or false., (i) ADH helps in water elimination, making the urine, hypotonic., (ii) Protein-free fluid is filtered from blood plasma, into the Bowman’s capsule., (iii) Henle's loop plays an important role in, concentrating the urine., (iv) Glucose is actively reabsorbed in the proximal, convoluted tubule., (NCERT Exemplar), , (ii) Cockroaches, (iv) Amphioxus, —, —, —, —, , Flame cells, Malpighian tubules, Protonephridia, Nephridium, , 9. What will happen if the stretch receptors of the, urinary bladder wall are totally removed? Explain., Ans. As urine collects in the urinary bladder, the muscular, , walls of the bladder distend to accommodate it. The, stretch receptors on the walls of the bladder send signals, to the CNS by stimulating the sensory nerve ending in, the bladder. It causes an urge to pass out urine. So, if the, stretch receptors are totally removed from the bladder,, urine will not be collected in the bladder and urination, will keep continuing., , 10. Where do ultrafiltration, reabsorption and secretion, occur in a nephron?, Ans., , (i) Ultrafiltration occurs in Bowman’s capsule., (ii) Reabsorption occurs in PCT, loop of Henle, DCT, and collecting ducts., (iii) Secretion occurs in PCT, loop of Henle and DCT., , 11. Where does the urine formation take place? Name, the processes involved in the formation of urine., Ans. The process of urine formation is called uropoiesis. Urine, , formation occurs in the kidneys., It involves three steps, (i) Glomerular filtration (ii) Selective reabsorption, (iii) Tubular secretion, , 12. Give the name of the two actively transported, substances in glomerular filtrate. (NCERT Exemplar), Ans. Glucose and amino acids are actively transported, substances in glomerular filtrate., , 13. What is meant by the term osmoregulation?, Ans. It is the phenomena of regulation of change in the, , concentration of body fluids according to the, concentration of external environment, i.e. most marine, invertebrates, some freshwater invertebrates, hagfish, (a vertebrate)., , 14. Give the name of the layers through which the, glomerular capillary blood pressure causes, filtration., Ans. The layers through which the glomerular capillary blood, , pressure causes filtration are, (i) The endothelium of glomerular blood vessels., (ii) The epithelium of Bowman’s capsule., (iii) A basement membrane (present between these two, above mentioned layers)., , Ans., , (i) False and can be corrected as, ADH helps in increasing the reabsorbtion of water,, making the urine hypotonic., (ii) True, (iii) True, (iv) True, , 16. How does ADH regulate body fluid volume?, Explain., Ans. Excessive loss of fluid from the body activates, , osmoreceptors, which stimulate the hypothalamus to, release ADH from the neurohypophysis. ADH facilitates, water reabsorption from posterior parts of tubule. This, decreases osmolarity of blood. An increase in body fluid, volume can switch off the osmoreceptors and suppress, the ADH release to complete the feedback. ADH also, causes constrictory effects on blood vessels., , 17. Describe the role of alcohol and caffeine in the, concentration of urine., Ans. Alcohol inhibits the release of ADH and caffeine, , interferes with ADH action and sodium reabsorption., Thus, both of these artificially dilute the urine. Such, compounds which dilute urine are called diuretic, substances., , 18. How is glomerular filtrate hypertonic and, hypotonic in descending and ascending limb of loop, of Henle, respectively. What is the effect of ADH, on collecting tubules?, Ans. Counter-current system is found in two limbs of loop of, , Henle. The ascending limb transports Na + and some urea, into surrounding medullary tissue. It is impermeable to, water. So, it makes urine diluted or hypotonic. The walls, of descending limbs are permeable to water and salt, so, Na+ and water from surrounding fluid are absorbed. So,, the content of urine becomes hypertonic., ADH (Antidiuretic Hormone) is secreted when the, osmotic pressure of blood increases due to excess loss of, water and body. The hormone renders the walls of distal, convoluted tubule, Collecting Tubule (CT) and collecting, duct of a nephron permeable to water and increases the, reabsorption of water into the surrounding tissues and, particular capillaries. The urine becomes hyperosmotic, and less in volume and water is conserved in the body.

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129, , CBSE Term II Biology XI, , 19. State the importance of counter-current systems in, renal functioning., Ans. Counter-current mechanism has been evolved in higher, , vertebrates (birds and mammals including man) to excrete, hypertonic urine (urine is more concentrated than blood), for conserving body water so necessary for land life., , l, , Long Answer (LA) Type Questions, 1. (i) Study the given structure carefully and label the, parts given as A, B, C, D and E., (ii) Give one major function of each of these., A, , 20. Discuss the regulation of kidney function by the, , C, , heart., B, , Ans. Atrial Natriuretic Factor (ANF) is secreted by the atria of, , heart. It causes vasodilation (dilation of blood vessels), and thereby, decrease the blood pressure. ANF works, antagonistically to RAAS., , 21. Give full form of ANF. Name the organ that secretes, it. Under what condition of the body is it released?, Or Write a brief note on atrial natriuretic factor., , D, , Ans. ANF is commonly known as Atrial Natriuretic Factor., , ANF is a hormone produced by the walls of the atria of, the heart in response to an increase in blood volume and, pressure. It increases sodium excretion and decreases, blood pressure., ANF inhibits release of renin from Juxta Glomerular, Apparatus (JGA) and thereby, inhibits NaCl reabsorption, by the collecting duct and reduces aldosterone release, from the adrenal gland., , 22. Explain the autoregulatory mechanism of GFR., (NCERT), Ans. The mechanism by which the kidneys regulate the, , glomerular filtration rate is autoregulatory. It is carried, out by the juxtaglomerular apparatus. The apparatus is a, microscopic structure located between the vascular pole, of renal corpuscle and the returning DCT., It plays a vital role in regulating renal blood flow and the, GFR. Whenever there is a decline in the glomerular, filtration rate, the JG cells get activated and release renin, which further stimulates the glomerular blood flow and, thereby bring the Glomerular Filtration Rate (GFR) back, to normal., , 23. What is the role played by renin-angiotensin in the, regulation of kidney function?, Ans. Role Played by Renin-angiotensin in the Regulation of, , Kidney Function Renin is released from JGA on, activation due to fall in the glomerular blood, pressure/flow. Renin converts angiotensinogen in blood to, angiotensin-I and further to angiotensin-II., Angiotensin-II, being a powerful vasoconstrictor,, increases the glomerular blood pressure and thereby, GFR. Angiotensin-II also activates the adrenal cortex to, release aldosterone. Aldosterone causes reabsorption of, Na + and water from the distal parts of the tubule. This, also leads to an increase in blood pressure and GFR. This, complex mechanism is generally known as the, renin-angiotensin mechanism., , E, , Ans., , (i) A – Afferent arteriole, B – Proximal convoluted tubule, C – Glomerulus, D – Loop of Henle, E – Collecting duct, (ii) Following are the functions of each of the above, mentioned part, A – Carry blood to glomerulus for ultrafiltration., B – Selective reabsorption of useful substances., C – Ultrafiltration of blood., D – Maintenance of the high osmolarity of medullary, interstitial fluid., E – Reabsorption of water to form hypertonic urine., , 2. Describe the process of urine formation in the, nephron through filtration, reabsorption and, secretion., Ans. The formation of urine is the result of the processes like, , glomerular filtration, reabsorption and secretion. These, processes occur in different parts of nephrons., 1. Glomerular Filtration The first step of urine, formation is the filtration of blood. It is carried out, by the glomerulus. That is why this step is called, glomerular filtration., The blood rushes into the glomerular capillaries with, a high pressure and gets filtered across the thin walls, of the capillary. Everything but not the blood cells, and the proteins get filtered and such a filtrate is, called ultrafiltrate that gets into the capsular space in, Bowman’s capsule., 2. Selective Reabsorption This is the second step in, the formation of urine from filtrate. Most of the, material in the filtrate is reabsorbed by the renal

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130, , CBSE Term II Biology XI, , tubules. Thus, the process is called reabsorption., Depending upon the types of molecules being, reabsorbed, movements into and out of epithelial, cells in different segments of nephron occur either, by passive transport (e.g. water and urea) or active, transport (e.g. glucose and amino acids) or Na + (both, by active and passive)., 3. Tubular Secretion It is also an important step in, urine formation. Certain chemicals in the blood that, are not removed by filtration from the glomerular, capillaries are removed by this process of tubular, secretion. It helps in the maintenance of ionic and, acid-base balance of body fluids by removing, chemicals like foreign bodies, ions (K + , H + , NH+4 ), and molecules (medicines), etc., that are toxic at, elevated levels., , 3. Describe the disorders of excretory system., Ans. Malfunctioning of kidneys can lead to several disorders of, , the excretory system., Some of these are as follows, (i) Uremia It is the presence of an excessive amount of, urea in the blood. Urea is highly harmful as it, poisons the cells at high concentration and may lead, to kidney failure., (ii) Kidney Failure (renal failure) Partial or total, inability of kidneys to carry on excretory and, salt-water regulatory functions is called renal or, kidney failure., (iii) Renal Calculi It is the formation of stone or, insoluble mass of crystallised salts (calcium,, magnesium, phosphates and oxalates, etc.), formed, within the kidney., (iv) Glomerulonephritis It is the inflammation of, glomeruli of kidney., (v) Diabetes Insipidus (DI) It is a condition, characterised by excessive thirst and frequent, micturition., , 4. Define haemodialyser. Describe the process of, kidney transplantation., Ans. Artificial kidney is a machine that is used to filter blood of, , a person and the process involved is called haemodialysis., Haemodialyser is a cellophane tube suspended in a, dialysing fluid (salt-water solution) of the same, composition as that of plasma, but without nitrogenous, waste like urea., Kidney (Renal) transplantation involves grafting a kidney, from a healthy and compatible donor into a recepient, suffering from kidney failure in order to restore normal, kidney functioning in him/her. It is the most successful, form of transplantation. For this, family members or close, relatives are often approached for donating as this greatly, , reduces the risk of rejection from the immune system of, the host., However, certain drugs (medicines) can also prevent, rejection of the transplanted kidney by suppressing the, immune system of the host., l, , Case Based Questions, 1. Direction Read the following passage and answer, the questions that follows., Ammonia is the simplest form of nitrogenous waste, which is formed by the deamination of amino acids., It is highly soluble in water hence, is generally, excreted across the body surface by diffusion., Animals which excrete out ammonia as a, nitrogenous waste product are called ammoniotelic, and the phenomenon of urinary elimination of, nitrogen, mainly in the form of ammonia is called, ammonotelism., Terrestrial adaptation made the production of less, toxic forms of nitrogenous wastes like urea and uric, acid. Ammonia produced by metabolism is, converted into urea in liver and released into the, blood. It is then filtered and excreted out by the, kidneys. Uricotelic animals excrete out uric acid as, nitrogenous waste product due to limited access to, water. In such animals, ammonia is converted into, uric acid which can be stored and excreted in, crystalline form., (i) Which is the most toxic excretory product?, , Ans. Ammonia is the most toxic excretory product hence,, , requires a large amount of water for its removal., , (ii) Which of the following is an example of ureotelic, animal?, Antedon, Taenia, Musca and Rana tigrina, Ans. Rana tigrina (frog) excretes out urea as a nitrogenous, , waste, hence is a ureotelic animal., , (iii) Which animal excretes out uric acid?, Ans. Uric acid is excreted out as a waste product in reptiles,, , birds, snails and insects., , (iv) Write down the order of toxicity of different, excretory products from lower to higher., Ans. The order of toxicity of different excretory products from, , lower to higher is, Uric acid < Urea < Ammonia, i.e. uric acid is the least toxic form and ammonia is the, most toxic form and needs to be eliminated as and when, formed.

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131, , CBSE Term II Biology XI, , 2. Observe the given diagram and answer the questions, that follows., X, R, Q, , P, , S, A, , (i) What is the role of structure A shown above?, Ans. Glomerulus along with Bowman’s capsule is called, , Malpighian body or renal corpuscle. It filters out large, solutes from blood and delivers it small solutes to renal, tubule for modification., , (ii) Give one point of differentiation between labels R, and X., Ans. R denotes afferent arteriole and X is efferent arteriole. One, , point of differentiation in that the blood flowing in R is rich, in waste products whereas that flow in X is poor in waste, products or contains less quantity of it., , (iii) Identify X and write any one of its feature., Ans. X is efferent arteriole. It carries venous blood away from, , renal corpuscle., , (iv) Define podocytes., Ans. The outer parietal wall of glomerulus is composed of, , flattened (squamous) cells and the inner visceral wall is, made up of a special type of less flattened cell called, podocytes., , (v) Where do we find label ‘S’?, Ans. Label S is Proximal Convoluted Tubule (PCT) which is, , restricted to the cortical region of the kidney., , 3. Direction Read the following passage and answer the, questions that follows., The excretory system is the system of an organism’s, body that performs the function of excretion. It is, , responsible for the elimination of wastes produced, by homeostasis., The excretory system of humans consists of two, kidneys, two ureters, one urinary bladder and one, urethra., Every human has got two kidneys which are, mesodermal in origin. They are reddish-brown,, bean-shaped structures situated in the abdominal, cavity just behind the vertebral column and are, protected from backside by the last two pairs of, ribs, i.e. floating ribs., Being bean-shaped, the medial portion of kidney, is seen in the form of a deep notch called hilum., The kidney contains one million thin, long, much, convoluted tubular unit called nephrons., Two tubes of length 25-30 cm and a diameter of, about 3 mm pass obliquely through the posterior, wall of the bladder., The urinary bladder is roughly pear-shaped with, its wall composed of three layers, an outermost, loose connective tissue, the middle layer and the, innermost epithelium lining., The urethra extends from neck of the bladder to, the exterior., (i) What does the process of excretion involve?, Ans. The process of excretion involves removal of metabolic, , wastes from the body., , (ii) Give the name of vessel of peritubular capillaries, that runs parallel to the loop of Henle., Ans. Vasa recta., , (iii) Where are kidneys situated?, Ans. Kidneys are situated in the abdominal cavity between, , the last thoracic and third lumbar vertebrae., , (iv) State the structural and functional unit of kidney., Ans. The structural and functional unit of kidney is called, , nephron. A kidney contains one million nephrons., , (v) Name the part of excretory system that is, associated with temporary storage of urine., Ans. Urinary bladder is a reservoir of urine and stores it, , temporarily.

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Chapter Test, Multiple Choice Questions, , Assertion-Reasoning MCQs, , 1. The nitrogenous waste is excreted in the form of, nitrogenous pellet in, (a), (b), (c), (d), , fishes, sponges, reptiles, None of the above, , 2. The function of collecting duct is to, (a), (b), (c), (d), , reabsorb water, maintain osmolarity, maintain pH and ionic balance, All of the above, , (a) Both A and R are true and R is the correct explanation of A, (b) Both A and R are true, but R is not the correct explanation, of A, (c) A is true, but R is false, (d) A is false, but R is true, , 1. Assertion (A) Malpighian tubules are excretory organs, , 3. The functioning of the kidneys is efficiently monitored, and regulated by the hormonal feedback mechanism, involving, (a), (b), (c), (d), , Direction (Q. Nos. 1-5) Each of these questions contains, two statements, Assertion (A) and Reason (R). Each of, these questions also has four alternative choices, any, one of which is the correct answer. You have to select, one of the codes (a), (b), (c) and (d) given below., , hypothalamus, JGA, heart, All of the above, , in most of the insects., Reason (R) These help in excretion of urea and, creatinine., , 2. Assertion (A) Compared to uric acid, urea is a more, toxic excretory substance., Reason (R) Birds and insects are uricotelic., , 4. A decrease in blood pressure/volume will not cause, , 3. Assertion (A) ADH and RAAS work in response to low, , the release of, , blood volume and blood pressure., , (a), (b), (c), (d), , Reason (R) ANF works in response to high blood, volume and blood pressure., , renin, atrial-natriuretic factor, aldosterone, ADH, , Short Answer Type Questions, , 5. Use of an artificial kidney during haemodialysis may, result in, I. nitrogenous waste buildup in the body., II. non-elimination of excess potassium ions., , 1. How does the loop of Henle help in concentrating the, urine in mammals of terrestrial adaptation?, , 2. What happen during excessive loss of fluids from the, body?, , III. reduced absorption of calcium ions from, gastrointestinal tract., , 3. How are the major excretory products eliminated from, , IV. reduced RBC production., , 4. What is an artificial kidney?, , Which of the following options is the most, appropriate?, (a) II and III, (b) III and IV, (c) I and IV, (d) II and IV, , the body?, , Long Answer Type Questions, , 1. The glomerular filtrate in the loop of Henle gets, concentrated in the descending and then gets diluted, (NCERT Exemplar), in the ascending limbs. Explain., 2. Describe the role of different organs in the process of, excretion., , Answers, Multiple Choice Questions, 1. (c), , 2. (d), , 3. (d), , 4. (b), , Assertion-Reasoning MCQs, 1. (c), , 2. (b), , 3. (b), , 5. (b), , For Detailed Solutions, Scan the code

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133, , CBSE Term II Biology XI, , CHAPTER 08, , Locomotion and, Movement, In this Chapter..., l, , Muscles, , l, , Detailed Structure of a Skeletal Muscle, , l, , Mechanism of Muscle Contraction, , l, , Red and White Muscle Fibre, , Muscles, These are made up of highly specialised thin and elongated, cells called muscle fibres. Muscles arise from the, embryonic mesoderm. It makes about 40-50% of a human, body weight., , Special Properties, Muscles exhibit various special properties, some of them are, given below, (i) Contractibility The cells of muscle can be shorten, considerably and return to the original relaxed state., (ii) Excitability It is due to the energy stored in the, electrical potential difference across the plasma, membrane., (iii) Muscles also possess properties of extensibility and, elasticity (because of proteins actin and myosin)., , Types of Muscles, Muscles have been classified using different criteria,, i.e. location, appearance and nature of regulation of their, activities., , Based on their location, the muscles are of three types,, i.e. skeletal, visceral and cardiac., (i) Skeletal or Striated Muscles, These muscles function in association with the skeleton of, organism. Under the microscope, they show a striped, appearance and hence are called striated muscles., They are also known as voluntary muscles as their activities, are under the voluntary control of the central nervous system., They are primarily involved in locomotory actions and change, of body postures., (ii) Visceral or Smooth Muscles, They are found in the inner walls of hollow visceral (internal), organs of body like alimentary canal, reproductive tract, etc., They do not exhibit any striation and are smooth in appearance, and hence, are called smooth muscles (non-striated muscle)., They are also known as involuntary muscles as they are not, under the voluntary or direct control of the nervous system., They assist in the transportation of materials, e.g. movement of, food through the digestive tract and gametes through the, genital tract.

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134, , CBSE Term II Biology XI, , (iii) Cardiac Muscles, , muscle tissue. Both these proteins are arranged as rod-like, structures, parallel to each other and also to the, longitudinal axis of myofibrils. Actin filaments are thinner, than myosin filaments., , They occur in the wall of the heart and in walls of big veins, (e.g. pulmonary veins and superior vena cava), where these, veins enter the heart. These are striated and involuntary in, nature. Presence of oblique bands and intercalated discs are, their characteristic feature., These assemble in a branching pattern to form a cardiac, muscle. They never get fatigue., , Detailed Structure of a, Skeletal Muscle, Skeletal muscle is made up of a number of muscle bundles or, fascicles held together by fascia (collagenous connective, tissue layer)., , Composition of Muscle Bundle, Each muscle bundle contains a number of muscle fibres, (muscle cells), bounded by sarcolemma (plasma membrane), and contains well-developed endoplasmic reticulum, (sarcoplasmic reticulum), specialised for calcium storage in its, sarcoplasm (cytoplasm)., , Diagrammatic representation of, (a) Anatomy of a muscle fibre showing a sarcomere,, (b) A sarcomere, , l, , Blood vessels, , Muscle fibres or cells, , Fasciculus, or, Fascicle (muscle bundle), , Sarcolemma, , Diagrammatic cross-sectional view of a muscle showing muscle, bundles and muscle fibres, , Muscle fibre is a syncytium as its sarcoplasm contains many, nuclei. There are large number of parallel arrangement of, filaments called myofilaments or myofibrils (characteristic, feature of muscle fibre)., , Detailed Study of a Myofibril, l, , l, , A myofibril has alternate dark and light bands. The dark, bands are also called Anisotropic band or A-band which, contains protein myosin. The light bands are called, Isotropic band or I-band which contain protein actin., The striated appearance of myofibril is due to the, distribution pattern of the proteins, actin and myosin in the, , l, , l, , l, , Each I-band has its centre, a dark membrane called Z-line, (an elastic fibre). It is also called Z-disc or Krause’s, membrane or Dobie’s line. The part of the myofibril, between two successive Z-lines is called a sarcomere, (functional unit of muscle contraction)., A sarcomere consists of the A-band and half of each, adjacent I-band. A thin fibrous membrane called M-line, present in the middle of A-band holds the thick filaments, together., The A and I-bands are arranged alternately throughout the, length of myofibril. At the centre of A-band, a portion is, present that is not overlapped by thin filaments. It is called, the H-zone (Hensen zone)., In resting state, the edges of thin filaments on either side of, thick filaments partially overlap each other leaving H-zone, in the centre of thick filaments., , Structure of Contractile Proteins, The thick myofilaments are formed by myosin protein. The, thin myofilaments are formed by three types of proteins, called actin, tropomyosin and troponin. These four proteins, are collectively known as contractile proteins., , Thick Myofilament or Primary, Myofilament, It consists mainly of myosin protein. Each myosin filament is, a polymerised protein made up of many monomeric proteins, called meromyosins.

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135, , CBSE Term II Biology XI, , Each meromyosin has two important parts which are as follows, (i) Globular Head, It has a short arm, called Heavy Meromyosin (HMM)., The HMM components project outwards at regular distance, and angle from each other, from surface of a polymerised, myosin filament and known as cross arm., The globular head is an active ATPase enzyme, which has, binding sites for ATP and active sites for actin., , Mechanism of Muscle, Contraction, l, , l, , (ii) Tail, It is called the Light Meromyosin (LMM). The myosin, molecule has two identical heavy chains and four light chains., The two heavy chains wrap spirally around each other to form a, double helix. The light chains are the parts of the myosin heads, and help to control the function of head during the contraction, of muscle., , l, , l, , Head, , Actin binding sites, ATP binding sites, , Cross arm (HMM), , (LMM), , l, , Myosin monomer (meromyosin), , Thin Myofilament or Secondary, Myofilament, It is composed of following proteins, (i) Actin, It is a globular protein with low molecular weight. It is made up, of two ‘F’ (filamentous) actin helically wound to each other., Each F actin is a polymer of monomeric ‘G’ (globular) actins., (ii) Troponin, It is a complex protein of three globular peptides (Troponin-T,, Troponin-I and Troponin-C) distributed at regular intervals on, tropomyosin., Troponin complex, Tropomyosin, F-actin, , An actin (thin) filament, , In the resting stage of muscle fibre, a subunit of troponin masks, the active sites for myosin on the actin filaments., (iii) Tropomyosin, Two filaments of this protein run close to the ‘F’ actins, throughout its length., , l, , The contraction of muscle is best explained by the, sliding filament theory. It states that contraction of, muscles takes place by the sliding of thin and thick, filaments (that are placed over each other) with the help, of cross-bridge. It reduces the length of the sarcomere., This theory was proposed independently by AF Huxley, and R Niedergerke and by HE Huxley and Jean, Manson in England in 1954., The sequence of events leading to contraction is initiated, by a signal in the Central Nervous System (CNS), either, from the brain (voluntary activity) or from spinal cord, (reflex activity) via a motor neuron., A motor neuron along with the muscle fibres connected, to it, forms a motor unit and the action potential is, conveyed to a motor end plate at neuromuscular, junction, i.e. it is the junction between a motor neuron, and sarcolemma of muscle fibre., A neurotransmitter (acetylcholine) is released at the, junction by the neural signal which generates an action, potential in the sarcolemma. This spreads and causes the, release of calcium ions into sarcoplasm., Calcium plays a key regulatory role in muscle, contraction. Increase in calcium ions level leads to, binding of Ca + ions the troponin subunit on actin, filament. This removes the masking of active sites for, myosin., , Formation of Cross-Bridge, An ATP molecule joins the active site on myosin head of, myosin myofilament. These heads contain an enzyme,, myosin ATPase that along with Ca 2+ and Mg 2+ ions, catalyse the breakdown of ATP., ATPase, ATP Myosin, , → ADP + Pi + Energy, Ca 2+ , Mg 2+, , The energy is transferred to myosin head, which energises, and straightens to join an active site on actin myofilament,, forming a cross-bridge., The energised cross-bridges move, causing the attached, actin filaments to move towards the centre of A-band. The, Z-line is also pulled inwards causing shortening of, sarcomere, i.e. contraction. It is clear from the above, explanation that during contraction, A-bands retain the, length, while I-bands get reduced.

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136, , CBSE Term II Biology XI, , The myosin head releases ADP and Pi, relaxes to its low energy state. The head detaches from actin myofilaments when new, ATP joins it (cross-bridge broken)., Actin filament, P, ADP + Pi, , ADP, , Myosin, filament, ATP, , ADP and Pi, remain attached, to myosin head, , Myosin head attaches, to actin filament, , Cross-bridge, , ATP binds to myosin head,, causing dissociation, (Breaking of cross-bridge), , (Formation of cross-bridge), P, ADP, , Pi and, ADP released, (Sliding/Rotation), , Stages in cross-bridge formation, rotation of head and breaking of cross-bridge, , l, , In repeating cycle, the free head cleaves the new ATP. The, cycles of cross-bridge formation and breakage is repeated, causing further sliding., H-zone, , I-band, , A-band, , Red and White Muscle Fibres, Birds and mammals have two kinds of striated muscle fibres,, in their skeletal muscles, i.e. red (slow) and white (fast) muscle, fibres., Differences between Red and White Muscle Fibres, , Relaxed, , Red Muscle Fibres, Z-line, , Z-line, , Z-line, , Contracting, , Maximally, contracted, Two sarcromeres, Sliding filament theory of muscle contraction, , Muscle Relaxation, After contraction, the calcium ions are pumped back to the, sarcoplasmic cisternae, blocking the active sites on actin, myofilaments. The Z-line returns to original position, i.e., relaxation of muscle fibre takes place., , White Muscle Fibres, , They are dark red muscle They are pale or whitish as they have, fibres due to the presence less myoglobin., of abundant myoglobin in, them., Mitochondria are more in Mitochondria are few in number, but, number, but they have, amount of sarcoplasmic reticulum is, less sarcoplasmic, high., reticulum., They depend on aerobic, process for energy., , They depend on anaerobic process for, energy., , They have slow rate of, contraction for long, periods., , They have fast rate of contraction for, short periods., , e.g. extensor muscle of the e.g. eyeball muscles., human back.

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137, , CBSE Term II Biology XI, , Chapter, Practice, PART 1, Objective Questions, l, , Multiple Choice Questions, 1. Locomotory actions within human body are carried, out using, , (a) unstriped muscles, (b) striated muscles, (c) involuntary muscles, (d) visceral muscles, Ans.(b) Locomotory actions within human body are carried out, using striated muscles or skeletal muscles. These muscles, are closely associated with the skeletal components of the, body and are primarily involved in locomotory actions, and changes of body postures., , 2. The storehouse of calcium ions in the muscle, fibre is, (a) smooth endoplasmic reticulum, (b) Golgi body, (c) sarcoplasmic reticulum, (d) lysosomes, Ans.(c) The storehouse of calcium ions in the muscle fibre is, sarcoplasmic reticulum., , 3. The muscle bundles, fascicles are held together by, the collagenous connective tissue called, (a) intercalated disc, (c) fascia, Ans. (c), , (b) myofibril, (d) All of these, , 4. Choose the incorrect pair., (a) Globular head of meromyosin – Active ATPase enzyme, (b) Thin fibrous membrane holding – M-line thick, filaments in A-band, (c) Dark bands – Isotropic band, (d) None of the above, Ans.(c) The pair in option (c) is incorrect and can be corrected, as, Dark bands are called A-bands or Anisotropic bands, whereas light bands are Isotropic or I-bands., Rest of the pairs are correctly matched., , 5. In the centre of each I-band, there is an elastic fibre, called, (a) I-line, (b) Z-line, (c) A-line, (d) H-zone, Ans. (b) In the centre of each I-band, there is an elastic fibre, called Z-line, which bisects it. The thin filaments are, firmly attached to the Z-line., , 6. The H-zone in the skeletal muscle fibre is due to, (a) the absence of myofibrils in the central portion of, A-band, (b) the central gap between myosin filaments in the, A-band, (c) the central gap between actin filaments extending, through myosin filaments in the A-band, (d) extension of myosin filaments in the central portion of, the A-band, Ans. (c) The H-zone in the skeletal muscle fibres is the central, gap between actin filaments extending through myosin, filaments in the A-band. Alternate arrangement of dark, and light bands gives the striated appearance to a, skeletal muscle. At the centre of A-band, a comparatively, less dark zone called H-zone is present., , 7. Cross arms of the myosin monomer consist of, (a) outward projection of G-actin filament, (b) outward projection of the head region of meromyosin, (c) outward projection of the tail region of meromyosin, (d) Both (b) and (c), Ans. (b) The cross arms of myosin monomer consist of a head, and short arm which projects outwards at regular distance, and angle from each other, from the surface of, polymerised myosin filament. The globular head is an, active ATPase enzyme and has binding sites for ATP and, active sites for actin., , 8. Active binding sites for actin are located on, (a) troponin, (c) meromyosin, , (b) tropomyosin, (d) Both (a) and (c)

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138, , CBSE Term II Biology XI, , Ans. (c) Active (binding) sites for actin are located on the, , globular head of a meromyosin. The globular head is an, active ATPase enzyme which contains binding sites for, both ATP and actin., , 9. Identify A, B and C in the given diagram., A, , Codes, A B C D, (a) 1 2 4 3, (b) 2 1 3 4, (c) 2 1 4 3, (d) 3 2 4 1, Ans. (c) A–2, B–1, C–4, D–3, , 14. Muscle contains a red coloured oxygen containing, , B, C, , (a) A–Troponin, B–Tropomyosin, C– F-actin, (b) A–Thick filament, B–Troponin, C–Tropomyosin, (c) A–Myosin filament, B–Troponin, C–Tropomyosin, (d) A–Meromyosin, B–Troponin, C–Tropomyosin, Ans.(a) The given diagram is of an actin filament in which A is, troponin B is tropomyosin and C is F-actin., , 10. Action potential in the sarcolemma of muscles is, , pigment called, (a) rhodopsin, (b) myoglobin, (c) haemocyanin, (d) Both (a) and (b), Ans. (b) Muscles contain a red coloured oxygen containing, pigment called the myoglobin. It is abundantly found in, the red muscle fibres than white muscle fibres., , 15. Aerobic muscles and anaerobic muscles are called, , generated by, (a) neuroinhibitors, (b) acetylcholine, (c) methylcholine, (d) ethylcholine, Ans. (b) A neural signal reaching neuromuscular junction, releases a neurotransmitter, i.e. acetylcholine. It, generates an action potential in the sarcolemma. This, spreads through the muscle fibre and causes the release, of calcium ions into the sarcoplasm., , 11. Which muscle band remains unchanged during the, contraction and relaxation of the skeletal muscle?, (a) I, (b) H, (c) A, (d) E, Ans. (c) A-band or Anisotropic band remains unchanged, during the contraction and relaxation of the skeletal, muscles. The H-zone narrows and even disappears when, the thin myofilaments meet at the centre of the, sarcomere. The size of I-band also decreases., , 12. For how long, contraction of the muscles continues, in sliding filament theory?, (a) Till ATP binds to myosin head, (b) Till ADP binds to myosin head, (c) Till Ca 2+ present in sarcoplasm, (d) Till polymerisation of myosin head is going on, Ans. (c) Sliding of actin and myosin filaments continues till the, Ca 2+ ions are pumped back to the sarcoplasmic cisternae,, resulting in the masking of actin filaments. This causes, the return of Z-lines back to their original position, i.e., relaxation of muscle fibre., , 13. Match the following columns., Column I, , Column II, , A. Fast muscle fibres, , 1., , Myoglobin, , B. Slow muscle fibres, , 2., , Lactic acid, , C. Actin filament, , 3., , Contractile unit, , D. Sarcomere, , 4., , I-band, , (a) red fibres; white fibres, respectively, (b) white fibres; red fibres, respectively, (c) white fibres; yellow fibres, respectively, (d) red fibres; yellow fibres, respectively, Ans. (a) Aerobic muscles and anaerobic muscles are called red, and white fibres, respectively., l, , Assertion-Reasoning MCQs, Direction (Q. Nos. 1-5) Each of these questions, contains two statements, Assertion (A) and Reason, (R). Each of these questions also has four alternative, choices, any one of which is the correct answer. You, have to select one of the codes (a), (b), (c) and (d), given below., (a) Both A and R are true and R is the correct explanation, of A, (b) Both A and, R are true, but R is not the correct explanation of A, (c) A is true, but R is false, (d) A is false, but R is true, , 1. Assertion (A) Muscle fibre is a syncytium., Reason (R) The sarcoplasm of muscle fibre contains, numerous nuclei., Ans. (a) Both A and R are true and R is the correct explanation, , of A., Muscle fibre is a syncytium as its sarcoplasm contains, many nuclei., , 2. Assertion (A) The myosin rich zone called A-band, maintains its length during sarcomere contraction., Reason (R) The length of I-band remains the same, during muscle contraction., Ans. (c) A is true, but R is false. R can be corrected as, , The length of the I-band shortens during muscle, contraction.

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139, , CBSE Term II Biology XI, , The formation of cross-bridges causes the pulling of the, attached actin filaments towards the centre of A-band., The Z-line attached to these actins are also pulled, inwards thereby, causing a shortening of the sarcomere,, i.e. contraction. During the shortening of the muscle, the, I-bands get reduced, whereas the A-bands retain its, length., , l, , Case Based MCQ, 1. Observe the diagram given below and answer the, questions that follows., C, B, D, , 3. Assertion (A) On stimulation, a muscle cell releases, calcium ions (Ca 2+ ) from sarcoplasmic reticulum., Reason (R) By reacting with a protein complex,, Ca 2+ uncover active sites on the actin filaments., Ans. (b) Both A and R are true, but R is not the correct, , explanation of A., A neural signal reaching the neuromuscular junction, releases a neurotransmitter (acetylcholine) which, generates an action potential in the sarcolemma. This, spreads through the muscle fibre and causes the release, of calcium ions into the sarcoplasm., Increase in Ca + levels leads to the binding of calcium to, the subunit of troponin on actin filaments and thereby, removes the masking of active sites for myosin., , 4. Assertion (A) Calcium is required for skeletal, muscle contraction., Reason (R) Calcium influx releases acetylcholine at, neuromuscular junction., Ans. (c) A is true, but R is false. R can be corrected as, , Calcium ions are required for skeletal contraction., Sarcoplasmic reticulum releases Ca + on receiving, stimulus at the neuromuscular junction or motor end, plate. When a neural signal reaches the neuromuscular, junction, a neurotransmitter called acetylcholine is, released at this junction and generates an action potential, in the sarcolemma. This spreads throughout the muscle, fibre and causes the release of the calcium ions into the, sarcoplasm., , 5. Assertion (A) Red muscle fibres depend on, anaerobic process for energy., Reason (R) Red muscle fibres have more number of, mitochondria in them., Ans. (d) A is false, but R is true. A can be corrected as, , Red muscle fibres have more number of mitochondria but, less sarcoplasmic reticulum. These fibres are dark red in, colour due to the presence of myoglobin. These carry out, aerobic respiration., White muscle fibres depend on anaerobic process for, energy as, number of mitochondria are also few in them,, but the amount of sarcoplasmic reticulum is huge., , A, , (i) Identify A and B., (a) Fascicle, Muscle fibre, (b) Muscle cell, Muscle bundle, (c) Sarcolemma, Muscle bundle, (d) Muscle cell, Muscle fibre, Ans. (a) A–Fascicle and B–Muscle fibre, , (ii) A is held together by, (a) myofibrils, (b) fascia, (c) fasicle, (d) sarcomere, Ans. (b) Muscle bundle or fascicle (A) is held by fascia., , (iii) B contain well-developed sarcoplasmic reticulum, also known as, (a) ectoplasmic reticulum, (b) sacrolemma, (c) endoplasmic reticulum, (d) Both (a) and (c), Ans. (c) Muscle fibre contain well-developed sacroplasmic, reticulum also known as endoplasmic reticulum., , (iv) Identify C., (a) Sarcolemma, (b) Sarcomere, (c) Sarcoplasm, (d) Myofibrils, Ans. (a) C represents sarcolemma., , (v) Thin filament of myofibril contains two F-actins and, two other proteins namely …P… and …Q… ., P, Q, (a) Actin, Myosin, (b) Troponin, Actin, (c) Troponin, Tropomyosin, (d) Meromyosin, Meromyosin, Ans. (c) Thin filament of myofibril contains two F-actins and, two other proteins namely troponin and tropomyosin.

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140, , CBSE Term II Biology XI, , PART 2, Subjective Questions, l, , Short Answer (SA) Type Questions, 1. Mention and explain the special properties of muscle., , Ans. The special properties exhibited by muscles are, , (i) Contractibility The cells of muscle can be shorten, considerably and return to the original relaxed state., (ii) Excitability It is due to the energy stored in the, electrical potential difference across the plasma, membrane., (iii) Muscles also possess properties of extensibility and, elasticity (because of proteins, actin and myosin)., , 5. Write true or false. Correct each false statement to, make it true., (i) Actin is present in thin filament., (ii) H-zone of striated muscle fibre represents both, thick and thin filaments., (iii) In a muscle fibre, Ca 2+ is stored in nucleus., (iv) Thin filaments of myofibrils contain 2 F-actins., (NCERT), Ans., , 2. How do you distinguish between a skeletal muscle, and a cardiac muscle., , (NCERT), , Ans. Differences between skeletal muscle and cardiac muscle, , are as follows, Skeletal Muscle, , Cardiac Muscle, , It is found in limbs, tongue, all It is found in the walls of, parts in association with the, heart and large veins., skeleton of organism., Fibres are unbranched., , Fibres are branched., , It is multinucleate., , It is uninucleate., , No oblique bridge and, intercalated discs., , Oblique bridges and, intercalated discs are, present., , It gets fatigued soon., , It never gets fatigued., , It is voluntary in nature., , It is involuntary., , (i) True, (ii) False, H-zone of striated muscle fibre represents, only thick filaments., (iii) False, in a muscle fibre, Ca 2+ is stored in, sarcoplasmic reticulum., (iv) True, , 6. Name the two important parts of meromyosin., Ans. Two important parts of meromyosin are, , (i) Globular head with short arm, called Heavy, Meromyosin (HMM)., (ii) Tail, called the Light Meromyosin (LMM)., , 7. Draw the diagram of a sarcomere of skeletal muscle, showing different regions., , (NCERT), , Ans., , 3. Give a brief account of visceral muscles. Mention, their function., Ans. Visceral or smooth muscles are found in the inner walls of, , hollow visceral (internal) organs of body like alimentary, canal, reproductive tract, etc. They do not exhibit any, striation and are smooth in appearance and hence, are, called smooth muscles (non-striated muscle). They are, also known as involuntary muscles as they are not under, the voluntary or direct control of the nervous system., They assist in the transportation of materials,, e.g. movement of food through the digestive tract and, gametes through the genital tract., , 4. Sarcolemma, sarcoplasm and sarcoplasmic, reticulum refer to a particular type of cell in our, body. Which is this cell and to what parts of that, cell do these names refer to?, (NCERT Exemplar), Ans. The cell is muscle., , These names refer to the following parts, Sarcolemma–Plasma membrane, Sarcoplasm–Cytoplasm, Sarcoplasmic reticulum–Endoplasmic reticulum, , Diagrammatic representation of (a) Anatomy of a muscle fibre, showing a sarcomere, (b) A sarcomere, , 8. Describe the important steps in muscle contraction., (NCERT), Ans. Following are the steps involved in skeletal muscle, , contraction, (i) Stimulation, (a) Nerve impulse arrives at neuromuscular junction, and release of acetylcholine takes place., (b) Spreading of action potential through muscle, fibre., (c) The release of Ca 2+ from sarcoplasmic reticulum, to cytoplasm of muscle fibre.

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141, , CBSE Term II Biology XI, , (ii) Contraction, (a) ATP joins to meromyosin head that hydrolyses into, ADP and Pi releasing energy, which in turn raises the, head to high energy state (the head joins active site on, actin, forming cross-bridge)., (b) ADP and Pi are released and head returns to low, energy state., (c) Actin filament is thus, pulled towards centre of, sarcomere. And a new ATP joins head, detaching it, from actin filament., (d) Above mentioned steps are thus, repeated many times, during one contraction to draw the thin myofilaments, further inward., , (ii) Increased consumption of oxygen and increased, production of CO2 stimulates the respiratory, centres, which causes the change of breathing rate., , 12. What kind of muscle fibres are richly found in the, extensor muscles of the back?, What characteristics enable these fibres to serve, their purpose?, Ans. Red striated muscle fibres are richly found in the, , extensor muscles of the back., Their abundant myoglobin and mitochondria enable, them to serve their purpose., , 13. Why is muscle fibre a syncytium? How are, myofilaments arranged in it?, , 9. What is the role of calcium in muscle contraction?, Ans. Calcium is important in skeletal muscle contraction, , Ans. Muscle fibre is a syncytium as the sarcoplasm contains, , because it binds to troponin to unmask/expose the active, sites on actin for myosin binding. By utilising the energy, from ATP hydrolysis, the myosin head now binds to the, exposed active sites on actin to form a cross-bridge., This pulls the attached actin filaments towards the centre, of A-band and the Z-line attached to these actins are also, pulled inwards thereby, causing contraction of muscle., , many nuclei. Myofilaments are parallelly arranged and, are present in large number in muscle fibre., , 14. Why are muscles rigidly locked in whatever, position they are after death? What is the, phenomenon known as?, Ans. Muscles require ATP to relax as well as to contract. On, , animal’s death, its muscles soon exhaust ATP and lose, the ability to contract or relax. They become rigidly, locked in whatever position they were when ATP gets, completely used up. This phenomenon is known as, Rigor Mortis. It is used in determining the time of, death., , 10. (i) How does a muscle return to its original form, during relaxation? Also draw a diagram showing, relaxation of muscle., (ii) What causes muscle fatigue?, Ans., , (i) The calcium ions after contraction are quickly pumped, back to the sarcoplasmic cisternae. This leads to, blocking of active sites on actin myofilaments., The Z-line returns to the original position. Causing, muscles to return to its original position, i.e. relaxation, form., H-zone, , I-band, , A-band, , Relaxed, , Long Answer (LA) Type Questions, 1. Differentiate between, (i) Actin and myosin filaments,, (ii) A-band and I-band,, (iii) Non-muscular and muscular movements, , Ans., Z-line, , Z-line, , Z-line, , (ii) Repeated activation of the muscles leads to, accumulation of lactic acid due to anaerobic, breakdown of glycogen in them which causes fatigue., , 11. Radha was running on a treadmill at a great speed for, 15 minutes continuously. She stopped the treadmill, and abruptly came out. For the next few minutes, she, was breathing heavily/fast. Answer the following, questions., (i) What happened to her muscles when she, strenuously exercised?, (ii) How did her breathing rate change?, (NCERT Exemplar), Ans., , l, , (i) By strenuous exercise, the metabolism of the muscle, increases, which leads to increased consumption of, oxygen and ATP. To meet this demand, blood supply of, muscle is also enhanced., , (i) Differences between actin and myosin filaments, are as follows, Actin Filaments, , Myosin Filaments, , These are found in I-band. These are found in A-band., These are thin., , These are thick., , Cross-bridges (heads) are, absent., , Cross-bridges (heads) are, present., , It is a globular protein, with low molecular, weight., , It is a heavy molecular, weight polymerised, protein., , (ii) Differences between A-band and I-band are as, follows, A-Band, , I-Band, , It is formed of myosin, filaments., , It is formed of only actin, filaments., , It gives dark appearance., , It gives light appearance.

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142, , CBSE Term II Biology XI, It has a light H-zone in the, centre., , It has dark Krause's, membrane in the centre., , It is anisotropic band which It is isotropic band which, possesses only one type of, possesses two types of, proteins., proteins., , (iii) Differences between non-muscular and muscular, movements are as follows, Non-muscular Movements Muscular Movements, These movements include, pseudopodial and ciliary, movements., , These movements are, brought about by, movement of myofilaments, within muscle firbres., , They persist in the animals, in some of their cells., , These are found in, majority of animals., , 2. Explain sliding filament theory of muscle, contraction with neat sketches., , (NCERT Exemplar), , given by two individual groups of scientists AF Huxley, and R. Niedergerke and by HE Huxley and Jean, Manson. The muscle contraction begins when the, neural signal reaches the neuromuscular junction from, CNS via motor neurons which release acetylcholine., The acetylcholine present in the synaptic cleft binds to, the receptor sites of motor end plate and cause its, depolarisation which creates an action potential., The induced action potential reaches sarcoplasmic, reticulum of muscle fibre and cause the relase of, Ca 2+ ions. These Ca 2+ ions bind to troponin and change, their shape which in turn change the shape of, tropomyosin and expose the active sites on the F-actin., Then the myosin cross-bridge is able to bind with the, active sites in the presence of myosin, ATPase, Ca 2+, ions and Mg 2+ ion, ATP breaks down into ADP and, phosphate and energy is released in the head., I-band, , Case Based Questions, 1. Direction Read the following passage and answer the, questions that follows., In a biology class, Amit read that human body, contain different muscles, depending upon the, functions of associated organs. He also learnt about, the structure of these muscles and found that skeletal, muscles anatomy is of great significance., (i) Which type of muscles are found in visceral organs, of body?, , Ans. Visceral organs are lined by smooth muscles. These are, , non-striated in appearance., , (ii) Name the muscles which are controlled voluntarily, and non-voluntarily, respectively., Ans. Skeletal or striated muscles are controlled voluntarily, , Ans. The sliding filament theory of muscle contraction was, , H-zone, , l, , A-band, , whereas cardiac and smooth muscles are controlled, involuntarily., , (iii) Mention two structural characteristics of cardiac, muscles., Ans. Cardiac muscles are branched, striated in appearance and, , possess intercalated discs., , (iv) Name two important proteins which form light and, dark bands in skeletal muscles., Ans. Light bands in skeletal muscles are formed by actin protein, , whereas the dark bands are composed of myosin protein., , 2. Direction Read the following passage and answer the, questions that follows., Akhil, a class XI student is very casual regarding his, studies. One day, his classes were suppose to, commence from 8 : 00 AM. But he left his home at 7 : 45, AM. He started running on his way, but after 400-500, m, he felt a severe cramp in his leg. Due to this cramp,, he had to stop and he missed his morning class., (i) What is the reason of the muscle cramp?, Ans. Due to lack of oxygen, anaerobic respiration start in the, , Relaxed, Z-line, , Z-line, , Z-line, , muscle. This leads to accumulation of lactic acid in the, muscle which results in muscle cramp., , (ii) How could one get rid off the cramp?, Contracting, , Ans. One can get rid off it by resting for some time, so that, , normal breathing rate resumes., , (iii) Name the oxygen carrying pigment in muscles?, , Maximally, contracted, , Ans. Myoglobin or muscle haemoglobin is the oxygen carrying, Two sarcromeres, , Energised myosin head binds to actin filament. The, cross-bridge moves and causes this filament to slide, along the thick myofilament. Loss of energy causes the, myosins to move back to its original position. ATP binds, to myosin head, causing dissociation from actin and, muscle relaxes. This process continues till Ca 2+ are, pumped back to the sarcoplasmic cisternae, masking the, actin filaments. This causes relaxation of the muscles., , pigment of muscles., , (iv) What does the sliding filament theory states?, Ans. The sliding filament theory states that contraction of, , muscle takes place by the sliding of thin and thick filament, with the help of cross-bridge., , (v) What changes in I and A-bands occur during muscle, contraction?, Ans. During muscle contraction the I-band get reduced while, , the A-band retain its length.

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Chapter Test, Multiple Choice Questions, , 1. Visceral muscles are likely to be found in, (a), (b), (c), (d), , brain and spinal cord, digestive tract, biceps and triceps, All of the above, , 1. Assertion (A) Visceral muscles are smooth in, , 2. Myofilaments or Myofibrils are, (a), (b), (c), (d), , obliquely arranged filaments of muscle fibre, parallelly arranged filaments of muscle fibre, horizontally arranged filaments of muscle fibre, radially arranged filaments of muscle fibre, , 3. Which one is incorrectly matched?, (a), (b), (c), (d), , Heavy meromyosin, Smooth muscle, Red muscle, Troponin, , —, —, —, —, , Globular head, Involuntary muscle, Myoglobin, Fibrous protein, , 4. Actin and myosin filaments of muscles are also called, (a), (b), (c), (d), , thick and thin filaments, respectively, thin and thick filaments, respectively, black and white filaments, respectively, white and black filaments, respectively, , 5. Consider the following statements., I. In resting state, edges of thin filament partially overlap, the ends of thick filament., II. H-zone is the overlapped area of thick and thin, filaments., , Select the correct option., (a), (b), (c), (d), , (a) Both A and R are true and R is the correct explanation of A, (b) Both A and R are true, but R is not the correct explanation, of A, (c) A is true, but R is false, (d) A is false, but R is true, , appearance., Reason (R) Many muscles assemble in a branching, pattern to form a visceral muscle., , 2. Assertion (A) Biceps and triceps are antagonastic, muscles., Reason (R) The biceps flexes the arm and the triceps, straighten the arm., , 3. Assertion (A) There are similarities between the, locomotion of unicellular organism and multicellular, animal., Reason (R) Ciliary, fragellar and amoeboid movements, occur in unicellular organisms., , Short Answer Type Questions, , 1. Define myoglobin. What is its importance in muscles?, 2. Define the given terms, (i) Tropomyosin, (ii) Meromyosin, , 3. Write a short note on skeletal muscle., Long Answer Type Questions, , I is true, II is false, Both I and II are true, I is false, II is true, Both I and II are false, , 1. How does a muscle shorten during its contraction and, return to its original form during relaxation?, , 2. (i) Exchange of calcium between bone and extracellular, , Assertion-Reasoning MCQs, Direction (Q. Nos. 1-3) Each of these questions contains, two statements, Assertion (A) and Reason (R). Each of, these questions also has four alternative choices, any, one of which is the correct answer. You have to select, one of the codes (a), (b), (c) and (d) given below., , fluid take place under the influence of certain, hormones. What will happen if more of Ca 2 + is in, extracellular fluid?, (ii) What will happen if very less amount of Ca 2 + is in the, extracellular fluid?, , Answers, Multiple Choice Questions, 1. (b), , 2. (b), , 3. (d), , 4. (b), , Assertion-Reasoning MCQs, 1. (c), , 2. (a), , 3. (b), , 5. (a), , For Detailed Solutions, Scan the code

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144, , CBSE Term II Biology XI, , CHAPTER 09, , Neural Control, and Coordination, In this Chapter..., , l, , l, , l, , l, , l, , Neural System, , l, , Neuron : Structural and Functional Unit of Neural System, , l, , Generation and Conduction of Nerve Impulse, , l, , Human Nervous System, , Coordination is the process through which two or more, organs of the body interact and complement the, functions of each other. On the other hand, integration is, a process, which makes two or more organs to work as a, functional unit in harmony to carryout some vital, functions of the body., For instance, when we do exercise, we observe, significant increase in the rate of respiration, heartbeat,, blood flow, sweating, etc., to meet enhanced need of, nutrients and energy for increased activities of lungs,, heart, muscles and many other body organs., When we stop exercising, we witness that the increased, activities of lungs, heart, nerves, kidneys, muscles, etc.,, gradually return to normal. Thus during exercise,, functions of various organs of the body are coordinated, and integrated., In higher animals (including human), two types of system, have been developed for the control, coordination and, integration, i.e. nervous system and endocrine system., The nervous system provides an organised network of, neurons spreads throughout the body of animal., , The endocrine system provides chemical coordination of, organs and organ systems through hormones which act as, chemical messenger., , Neural System, l, , l, , The neural system is the control system of the body which, consists of highly specialised cells called neurons., The nervous system is present in most of the multicellular, animals. Its complexity increases from lower to higher, animals. The nervous system in Hydra is composed of only, network of neurons. In insects, the nervous system is present, along with the ganglia and neural tissue. Invertebrates have, relatively simpler nervous system than the vertebrates., , Human Neural System, l, , l, , The whole nervous system of human being is derived from, embryonic ectoderm., The human neural system is divided into two parts, (i) Central Neural System (CNS), (ii) Peripheral Neural System (PNS)

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145, , CBSE Term II Biology XI, , l, , l, , l, , The CNS includes the brain and the spinal cord. The brain, is the site of information processing and control., The PNS comprises of all the nerves of the body associated, with the CNS (brain and spinal cord)., The nerve fibres of the PNS are of two types, , They conduct nerve impulses towards the cell body and are, called afferent processes (receiving processes)., Dendrites, Nissl’s granules, , (a) Afferent Fibres They transmit impulses from, tissues/organs to the CNS., , l, , l, , Cell body, , (b) Efferent Fibres They transmit regulatory impulses, from the CNS to the concerned peripheral, tissues/organs., The PNS is divided into two divisions, i.e. somatic neural, system and autonomic neural system., The somatic neural system relays impulses from the CNS, to skeletal muscles, while the autonomic neural system, transmits impulses from the CNS to the involuntary organs, and smooth muscles of the body., , Nucleus, Schwann cell, Axon, Myelin sheath, Node of Ranvier, , Note The autonomic neural system is further classified into sympathetic, neural system and parasympathetic neural system., l, , Visceral nervous system is a part of PNS that comprises, whole complex of fibres, nerves, ganglia and plexuses, through which impulses from CNS are transmitted to and, from viscera., , Axon terminal, Synaptic knob, Structure of a neuron, , 3. Axon, l, , Neuron : Structural and Functional, Unit of Neural System, Neurons are the longest cells in the body. Human neural, system has about 100 billion neurons. Majority of the, neurons occurs in the brain (nearly 2 billion). Fully formed, neurons never divide and remain in interphase throughout, the life., A neuron is a microscopic structure composed of the, following three major parts, , l, , l, , 1. Cell Body (Cyton or Soma), Like a typical cell it consists of cytoplasm, nucleus and cell, membrane. The cytoplasm has typical cell organelles like, mitochondria, Golgi apparatus, rough endoplasmic reticulum,, ribosomes, lysosomes, certain granular bodies and Nissl’s, granules., Presence of Nissl’s granules is the characteristic of all, neurons., , 2. Dendrites (Dendrons), These are usually shorter, tapering and much branched, processes that project out of the cell body. They also contain, Nissl’s granules and may be one to several in number., , l, , It is a single, usually very long process of uniform, thickness. The part of cyton from where the axon arises is, called axon hillock (most sensitive part of neuron)., The axon does not have Nissl’s granules, cell organelles and, granular bodies. The axon ends (distal end) in a group of, branches, the terminal arborisation (axon terminals)., When terminal arborisations of the axon meet the dendrites, of another neuron to form a synapse, each branch, terminates as a bulb-like structure called synaptic knob, which possesses mitochondria and secretory vesicles, (containing chemicals called neurotransmitters). The axons, transmit nerve impulses away from the cell body to a, synapse or to a neuromuscular junction., There are two types of axon, (a) Myelinated In myelinated nerve fibres, Schwann cells, form myelin sheath around the axon. The gaps between, two adjacent myelin sheaths are called nodes of, Ranvier. Myelinated nerve fibres are found in cranial, and spinal nerves and white matter of brain., (b) Non-myelinated In non-myelinated nerve fibres,, Schwann cells do not form myelin sheath around the, axon and are without nodes of Ranvier. They are, commonly found in autonomic and somatic neural, systems.

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146, , Based on the number of axon and dendrites, the neurons are, divided into three types, (i) Multipolar Neurons These neurons have several, dendrites and an axon. They are found in cerebral, cortex., (ii) Bipolar Neurons These neurons have one dendrite and, one axon. They are present in the retina of eye., (iii) Unipolar Neurons These neurons have cell body with, one axon only. These are found usually in the, embryonic stage., Main Properties of Neural Tissue, The neural tissue has two outstanding properties, (i) Excitability It is the ability of nerve cells to generate, an electrical impulse in response to a stimulus by, altering the normal potential differences across their, plasma membrane., (ii) Conductivity It is the ability of nerve cells to rapidly, transmit the electrical impulses as a wave from the site, of its origin along with their length in a particular, direction., , Functions of Neural System, The nervous system serves the following important functions, (i) Control and Coordination Nervous system controls, and coordinates the working of all parts of the body so, that it functions as an integrated unit. This is achieved, by three overlapping processes, i.e. sensory input,, integration and motor output., (ii) Memory Nervous system stores the impressions of, previous stimuli and retrieves (recalls) these, impressions in future. These impressions are referred, to as the experiences or memory., (iii) Homeostasis Nervous system helps in the maintenance, of the body’s internal environment, i.e. homeostasis., , Generation and Conduction, of Nerve Impulse, Nerve impulse is a wave of bioelectric/electrochemical, disturbance that passes along a neuron during conduction of, an excitation., Impulse conduction depends upon, (i) Permeability of axon membrane (axolemma)., (ii) Osmotic equilibrium (electrical equivalence) between, the axoplasm and Extracellular Fluid (ECF) present, outside the axon., , The generation of a nerve impulse is the temporary reversal, of the resting potential in the neuron., It occurs in following three steps, , Polarisation (Resting Potential), In a resting nerve fibre (a nerve fibre that is not conducting, an impulse), the axoplasm (neuroplasm of axon) inside the, axon contains high concentration of K + and negatively, charged proteins and low concentration of Na +., (i) In contrast, the fluid outside axon contains a low, concentration of K + and a high concentration of Na +, and thus, forms a concentration gradient., (ii) These ionic gradients across the resting membrane are, maintained by the active transport of ions by the, sodium-potassium pump, which transports 3Na +, outwards and 2K + inwards (into the cell)., (iii) As a result, the outer surface of the axonal membrane, possesses a positive charge, while its inner surface, becomes negatively charged and therefore, is polarised., (iv) The electrical potential difference across the resting, plasma membrane is called as the resting potential., The state of the resting membrane is called polarised, state., , Depolarisation (Action Potential), When a stimulus of adequate strength (threshold stimulus) is, applied to a polarised membrane, the permeability of the, membrane to Na + ions is greatly increased at the point of, stimulation (site A)., (i) This leads to a rapid influx of Na + followed by the, reversal of the polarity at that site, i.e. the outer surface, of the membrane becomes negatively charged and the, inner side becomes positively charged. The polarity of, the membrane at the site A is thus, reversed and, neuron at that point is said to be depolarised., (ii) The electrical potential difference across the plasma, membrane at the site A is called the action potential,, (another name of nerve impulse)., , Axon, , Types of Neurons on the, Basis of Structure, , CBSE Term II Biology XI, , A, Na, - + +, +, +, +, -+, Na, - + +, +, +, +, -+, , +, +, Na and K channels, + +, - - + +, , -, , + + + +, - -, , - + + +, , +, -, , +, -, , +, -, , +, -, , +, -, , + + +, , +, , +, Axoplasm, +, + + +, Membrane of axon, , B, + +, + + + +, - - - + +, , -, , - + + +, , Diagrammatic representation of impulse conduction, through an axon

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147, , CBSE Term II Biology XI, , This process (reversal) repeats itself over and over, again and a nerve impulse is conducted through the, length of the neuron., , Repolarisation, (i) The rise in the stimulus induced permeability to Na + is, extremely short-lived. It is quickly followed by a rise in, membrane permeability to K + ., (ii) Within a fraction of a second, Na + influx stops and K +, outflow begins until the original resting state of ionic, concentration is achieved. Thus, resting potential is, restored at the site of excitation, which is called, repolarisation of the membrane. This makes the fibre, once more responsive to further stimulation., (iii) In fact, until repolarisation occurs, neuron cannot, conduct another impulse. The time taken for this, restoration is called refractory period., Knowledge Plus, l, , l, , When an impulse travels along a myelinated neuron,, depolarisation occurs only at the nodes of Ranvier. It leaps over, the myelin sheath from one node to the next. This process is, called saltatory conduction., This process accounts for the greater speed of an impulse, travelling along a myelinated neuron than along a, non-myelinated one. It is upto 50 times faster than the, non-myelinated nerve fibre., , Human Nervous System, The human nervous system can be categorised to, (i) Central Nervous System (CNS), (ii) Peripheral Nervous System (PNS), , Central Nervous System (CNS), It is the integrating and command centre of the nervous, system which consists of the brain and spinal cord, (as discussed earlier)., , The brain is the central information processing organ of our, body and acts as the ‘command and control system’of all body, activities ., Cerebral hemisphere, Cerebrum, , Corpus callosum, , Forebrain, , (iv) The stimulated negatively charged point on the outside, of the membrane sends out an electrical current to the, positive point next to it. As a result, a current flows on, the outer surface from site B to site A while on the, inner surface, current flows from site A to site B., , Brain, , Brain stem, , (iii) At adjacent sites, e.g. site B, the membrane (axon) has, positive charge (still polarised) on the outer surface and, a negative charge on its inner surface., , Thalamus, Hypothalamus, Midbrain, Pons, Hindbrain, Cerebellum, Medulla, Spinal cord, , Cerebral aqueduct, , Diagram showing sagittal section of the human brian, , It controls the following activities, (i) The voluntary movements and balance of the body., (ii) Functioning of vital involuntary organs,, e.g. lungs, heart, kidneys, etc., (iii) Thermoregulation, hunger and thirst., (iv) Circardian (24 hrs) rhythms of our body., (v) Activities of several endocrine glands and human, behaviour., (vi) It is also the site for processing of vision, hearing,, speech, memory, intelligence, emotions and thoughts., Location, The brain is the anteriormost part of the central neural, system, which is located in the cranium (cranial cavity) of the, skull., , Protective Coverings of the Brain, It is covered by three membranes or meninges (cranial, meninges), (i) The outermost membrane, the duramater is the tough, fibrous membrane adhering close to the inner side of, the skull., (ii) The middle membrane is very thin layer called, arachnoid membrane (arachnoid mater)., (iii) The innermost membrane, the piamater is thin, very, delicate, which is in contact with the brain tissue.

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148, Structure, The human brain is divisible into three main parts, (i) Forebrain, (ii) Midbrain, (iii) Hindbrain, (i) Forebrain, The forebrain consists of, Olfactory Lobes The anterior part of the brain is formed by, a pair of short club-shaped structures, i.e. the olfactory lobes., These are concerned with the sense of smell., l, , l, , l, , l, , l, , l, , l, , Cerebrum It is the largest and most complex of all the parts, of the human brain. A deep cleft divides the cerebrum, longitudinally into two equal halves. These are termed as the, left and right cerebral hemispheres. These hemispheres are, connected by a large band of myelinated fibres the corpus, callosum., The outer cover of cerebral hemisphere is called cerebral, cortex. The cerebral cortex is referred to as the grey matter, due to its greyish appearance (as neuron cell bodies are, concentrated here)., The cerebral cortex is greatly folded. The upward folds, gyri,, alternate with the downward grooves or sulci. Beneath the, grey matter, there are millions of myelinated nerve fibers,, which constitute the inner part of the cerebral hemisphere., The large concentration of medullated nerve fibres gives this, tissue an opaque white appearance. Hence, it is called the, white matter., Lobes A very deep and a longitudinal fissure, separates the, two cerebral hemispheres. Each cerebral hemisphere of the, cerebrum is divided into four lobes, i.e. frontal, parietal,, temporal and occipital lobes., In each cerebral hemisphere, there are three types of, functional areas, Sensory areas receive impulses from the receptors and, motor areas transmit impulses to the effectors., Association Areas These are large regions that are neither, clearly sensory nor motor in junction. They interpret the, input, store the input and initiate a response in light of, similar past experience. Thus, these areas are responsible for, complex functions like memory, learning, reasoning and, other intersensory associations., Diencephalon is the posterio-ventral part of the forebrain., Its main parts are as follows, Epithalamus is a thin membrane of non-nervous tissue. It is, the posterior segment of the diencephalon., The cerebrum wraps around a structure called thalamus,, which is a major coordinating centre for sensory and motor, signalling., , CBSE Term II Biology XI, , The hypothalamus that lies at the base of thalamus, contains a number of centres, which control body, temperature, urge for eating and drinking. It also contains, several groups of neurosecretory cells, which secrete, hormones called hypothalamic hormones., The inner parts of cerebral hemispheres and a group of, deeply associated structures like amygdala, hippocampus,, etc. They form a complex structure (limbic lobe or limbic, system) that are involved in the regulation of sexual, behaviour, expression of emotional reactions,, e.g. excitement, pleasure, rage and fear and motivation., (ii) Midbrain, The midbrain is located between the thalamus or, hypothalamus of the forebrain and pons of the hindbrain. A, canal called the cerebral aqueduct passes through the, midbrain., The dorsal portion of the midbrain mainly consists of two, pairs (i.e. four) of rounded swellings (lobes) called corpora, quadrigemina., (iii) Hindbrain, The hindbrain consists of, (a) Pons consists of fibre tracts that interconnect different, regions of the brain., (b) Cerebellum is the second largest part of the human, brain (means first being the cerebrum). It has very, convoluted surface in order to provide the additional, space for many more neurons., (c) Medulla oblongata is connected to the spinal cord and, contains centres, which control respiratory rhythm,, cardiovascular reflexes, gastric secretions and the, postural gestures of the body (vertigo)., , Spinal Cord, It forms the posterior part of the CNS, running mid-dorsally, in the neural canal of the vertebral column. In an adult, the, spinal cord is about 42-45 cm long. Its diameter varies at, different stages of growth., The spinal cord is formed of two types of nervous tissue, i.e., grey matter and white matter. The grey matter is, surrounded by white matter. It is consisted of groups of, myelinated axons., The spinal nerve tracts are divisible into two, ascending, (conducting sensory impulses towards brain) and, descending (conducting motor impulses from brain)., Spinal cord conducts impulses to and from the brain and, controls most of the reflex activities. It also provides a, means of communication between spinal nerves and the, brain.

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149, , CBSE Term II Biology XI, , Peripheral Nervous System (PNS), The peripheral nervous system consists of, 1. Somatic Nervous System (SNS), , Their functions in comparative manner in a nut shell are, given below, Functions of Sympathetic, Nervous System, , Functions of Parasympathetic, Nervous System, , Vasoconstriction in general and, vasodilation (brain, heart, lungs, and skeletal muscles), , Vasodilation of coronary vessel, , Dilates pupil, , Constricts pupil, , Increases lacrimal glands, secretion, , Inhibits lacrimal glands secretion, , Inhibits salivary glands +, digestive glands, , Stimulates secretion, , Accelerates heartbeat, , Retards heartbeat, , Dilates trachea, bronchi and, lungs, , Constricts these organs., , Inhibits gut peristalsis, , Stimulates it, , Contracts anal sphincter, , Relaxes anal sphincter, , Relaxes urinary bladder, , Contracts and relaxes this, , 2. The Autonomic Nervous System (ANS), , Increases adrenal secretion, , Inhibits it, , The autonomic nervous system is also known as visceral, nervous system, consists of the sympathetic and, parasympathetic nervous system. The former is called, thoracolumbar outflow and the latter is called craniosacral, outflow depending upon their origin., , Blood sugar increases (glucagon) Blood sugar inhibits (insulin), , 2. Autonomic Nervous System (ANS), , 1. Somatic Nervous System, The somatic nervous system contains nerves which relay, impulses from CNS to skeletal muscles. These can be further, categorised into cranial (from brain) and spinal nerves on the, basis of their origin., (i) Cranial Nerves, 12 pairs cranial nerves emerge specifically from the forebrain, and brain stem., (ii) Spinal Nerves, All spinal nerves are mixed, having sensory and motor fibres, in approximately equal numbers. In humans, 31 pairs of, spinal nerves are present as Cervical (8 pairs),, Thoracic (12 pairs), Lumbar (5 pairs), Sacral (5 pairs),, Coccygeal (1 pair)., , Semen ejaculation increases, , Increases external, genitalia and sex, , Increases sweat secretion, , Inhibits this, , Contracts arrector pili, , Relaxes these

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150, , CBSE Term II Biology XI, , Chapter, Practice, PART 1, Objective Questions, l, , Multiple Choice Questions, 1. The neural system is composed of highly, specialised cells called neurons that can, , (a) not divide once fully formed, (b) receive stimuli, (c) transmit impulses, (d) All of the above, Ans. (d) Neurons are the structural and functional unit of, neural system. These can receive the stimuli and transmit, impulses to various sensory structures. Neurons do not, divide or regenerate in human body., , 2. The neural organisation in given animal comprises, of, , Codes, A B C D, (a) 2 3 4 1, (b) 1 2 3 4, (c) 3 4 2 1, (d) 1 2 4 3, Ans. (c) A–3, B–4, C–2, D–1, , 4. Visceral nervous system found in human body, (a) is a part of peripheral nervous system, (b) comprises the complex of nerves, ganglia and plexuses, (c) constitutes the connection between CNS and the, viscera, (d) All of the above, Ans. (d) All the given statements about visceral nervous system, are correct., , 5. A neuron consists of two parts viz, dendrites and, axon. The given statement is, (a) True, (b) False, (c) Cannot say, (d) Partially true or false, Ans. (b) The given statement is false because, A neuron consists of three major parts viz, cell body,, dendrites and axon., , 6. Refer to the given diagram of typical neurons., III, , II, IV, , (a) network of neurons, (b) CNS and PNS, (c) CNS, (d) PNS, Ans. (a) The diagram represents Hydra. In Hydra, neural, organisation is made up of network of neurons., , 3. Match the following columns., Column I, , Column II, , A. CNS, , 1. From CNS to tissue/organ, , B. PNS, , 2. From tissue/organ to CNS, , C. Afferent fibres 3. Comprises of brain and spinal cord, D. Efferent, fibres, , 4. Comprises of nerves of body, , I, , Identify the parts where Nissl’s granules are likely, to be found., (a) Only I, (b) II and III, (c) III and IV, (d) I, II, III and IV, Ans. (b) Nissl’s granules are found in the cytoplasm of both cell, body (II) and dendrites (III). These are not found in, nucleus (I) and axon (IV).

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151, , CBSE Term II Biology XI, , 7. Given below are types of neurons and their, characteristics., I. Unipolar neuron – possesses one axon and one, dendrite, II. Bipolar neuron – possesses one axon and two, dendrites, III. Multipolar neuron – possesses two or more axons, Choose the incorrectly matched pairs., (a) Only III, (b) I and II, (c) I and III, (d) I, II and III, Ans. (d) All given types of neurons and their characteristics are, incorrectly matched pair and can be corrected as, Based on the number of axon and dendrites, the neurons, are multipolar (with one axon and two or more dendrites),, bipolar (with one axon and one dendrite) and unipolar, (cell body with one axon only)., , 8. Resting membrane potential is maintained by, (a) hormones, (b) neurotransmitters, (c) ion pumps, (d) None of these, Ans. (c) The ionic gradients across the resting membrane are, maintained by the active transport of ions by the sodium, potassium pumps (or ion pumps) which transport 3Na +, outward for every 2K + into the cell., , 9. Depolarisation of axolemma during nerve, conduction takes place because, (a) equal amount of Na + and K + move out across, axolemma, (b) only Na + move inside, (c) more Na + moves outside than K + moving outside, (d) None of the above, Ans. (b) Depolarisation of axolemma during nerve conduction, takes place because only Na + move inside., , 10. Match the following columns., Column I, A., B., , C., D., , Column II, , Synaptic vesicles, Electrical potential difference, across the resting plasma, membrane, Generation of a nerve impulse, Granular bodies found in the, cell body of a neuron, , Codes, A B C D, (a) 3 1 2 4, (c) 4 3 2 1, Ans. (a) A–3, B–1, C–2, D–4, , 1. Resting potential, 2. Action potential, , 3. Neurotransmitter, 4. Nissl’s granules, , inside is, Duramater → Arachnoid → Piamater, , 12. Read the following statements regarding left, cerebral hemisphere and select the option with, correct statements., I. It receives most modalities of sensory information, from right side of the body., II. It is usually larger than the right cerebral, hemisphere., III. It is dominant cerebral hemisphere in most, individuals., IV. It is connected to the right cerebral hemisphere, by the corpus callosum., Codes, (a) I and II, (b) II and III, (c) I, III and IV, (d) III and IV, Ans. (c) Statements I, III and IV are correct. Statement II is, incorrect and can be corrected as, Both cerebral hemispheres are of the same size., , 13. Which part of the human brain controls the urge for, eating and drinking?, (a) Forebrain, (b) Midbrain, (c) Hindbrain, (d) Spinal cord, Ans. (a) Hypothalamus is a part of forebrain that controls the, urge for eating and drinking., , 14. Match the Column I (the parts of the human brain), with Column II (the functions) and identify the, correct option from the codes given below., Column I, (Parts of Brain), A., B., C., D., , Cerebrum, Cerebellum, Hypothalamus, Midbrain, , Column II, (Functions), 1., 2., 3., 4., , Codes, A B C D, (a) 3 4 2 1, (c) 3 4 1 2, Ans. (d) A–4, B–3, C–1, D–2, , Controls the pituitary, Controls vision and hearing, Maintains body posture, Site of intelligence, , A B C D, (b) 4 3 2 1, (d) 4 3 1 2, , 15. Four rounded lobes in midbrain are, A B C D, (b) 2 3 1 4, (d) 1 4 3 2, , 11. Cranial meninges from outer layer to inner layer, are called, (a), (b), (c), (d), , Ans. (b) The correct sequence of meninges from outside to, , piamater, arachnoid, duramater, duramater, arachnoid, piamater, arachnoid, duramater, piamater, arachnoid, piamater, duramater, , (a) occipital condyles, (b) corpora quadrigemina, (c) corpora allata, (d) cerebral aqueduct, Ans. (b) The dorsal portion of the midbrain consists of four, round swellings (lobes) called corpora quadrigemina., The midbrain is located between the thalamus/, hypothalamus of the forebrain and pons of the hindbrain., A canal called the cerebral aqueduct passess through the, midbrain.

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152, l, , CBSE Term II Biology XI, , Assertion-Reasoning MCQs, Direction (Q. Nos. 1-5) Each of these questions contains, two statements, Assertion (A) and Reason (R). Each of, these questions also has four alternative choices, any one, of which is the correct answer. You have to select one of, the codes (a), (b), (c) and (d) given below., (a) Both A and R are true and R is the correct, explanation of A, (b) Both A and R are true, but R is not the correct, explanation of A, (c) A is true, but R is false, (d) A is false, but R is true, , 1. Assertion (A) Neurons are excitable cells., Reason (R) Membranes of the neurons are in a, polarised state which is responsible for the, excitability., Ans. (a) Both A and R are true and R is the correct explanation, , of A., Neurons are excitable cells because their membranes are, in a polarised state. This means that there is an electrical, difference across the cell membrane, i.e. the electrical, charge on the outside of the membrane is positive, while, the electrical charge on the inside of the membrane is, negative., , 2. Assertion (A) The imbalance in concentration of, Na + , K + and proteins generates resting potential., Reason (R) To maintain the unequal distribution of, Na + and K + , the neurons use electrical energy., Ans. (c) A is true, but R is false. R can be corrected as, , To maintain the unequal distribution of Na + and K + ions,, the nerves use chemical energy in the form of ATP to, actively transport Na + ions out of cell and K + more inside, the cell., , 3. Assertion (A) Arrival of an impulse at the axon, terminal, stimulates the release of, neurotransmitters in the synaptic cleft., Reason (R) These neurotransmitters are responsible, for the opening of ion channels., Ans. (a) Both A and R are true and R is the correct explanation, , of A., Arrival of an impulse at the axon terminal, stimulates the, release of neurotransmitters in the synaptic cleft because, neurotransmitters bind to specific receptors on the, membrane and change the membrane potential of the, neuron which opens the ion channels., , 4. Assertion (A) Midbrain is located above the, thalamus and hypothalamus., Reason (R) Cerebral aqueduct passes through, midbrain., Ans. (d) A is false, but R is true. A can be corrected as, , Midbrain is located between the thalamus (or, hypothalamus) of forebrain and pons of the hindbrain., , 5. Assertion (A) Injury to medulla could lead to death., Reason (R) Medulla contains centre of respiration, and cardiovascular reflexes., Ans. (b) Both A and R are true, but R is not the correct, , explanation of A., Medulla contains the control center of all vital activities, of bodies like respiration, heartbeat, etc. Thus, any injury, to this part could result in death of an individual., l, , Case Based MCQ, 1. Direction Read the following passage and answer, the questions that follows., The brain is one of the most complex organs in, human body. It controls all the functions of the, body, interprets information from the surroundings,, control emotions, store memory, etc. Protected, within the skull, this master structure is composed, of cerebrum, cerebellum and brain stem. All these, structures are found at different locations and, perform varied functions. The brain has hollow, fluid-filled cavities called ventricles. Inside these, ventricles, choroid plexus secretes cerebrospinal, fluid. It helps the brain from injuries., (i) The structure that relay signals from forebrain to, cerebellum is, , (a) corpus callosum, (b) medulla oblongata, (c) limbic system, (d) pons, Ans. (d) Pons connects the regions of forebrain to cerebellum, and thus, acts as relay centre., , (ii) Aqueduct of Sylvius connects, (a) lateral ventricle to third ventricle, (b) third ventricle to fourth ventricle, (c) fourth ventricle to subarachnoid space, (d) first ventricle to second ventricle, Ans. (b) Aqueduct of Sylvius connects the third and fourth, ventricles. It is a long narrow tube within which CSF flows., , (iii) Cerebrospinal fluid contains excessive amount of, (a) K + ions, (b) Ca 2+ ions, +, (c) Na ions, (d) Mg 2+ ions, Ans. (c) CSF contains about 150 mEq/L of Na + ions, 2.9 mEq/L, of K + ions and 2.3 mEq/L each of Ca 2+ and Mg 2+ ions., Thus, it contains excessive amount of Na + ions., , (iv) Brain stem is formed by, (a) four lobes of cerebrum (b) epithalamus and thalamus, (c) cerebellum and medulla (d) midbrain and hindbrain, Ans. (d) Brain stem is formed by midbrain and hindbrain., , (v) The surface of cerebrum is called, (a) arachnoid, (b) piamater, (c) cortex, (d) cranium, Ans. (c) Cortex is the surface of cerebrum that contains billions, of neurons. To accommodate these neurons, cortex gets, folded to form sulci and gyri.

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153, , CBSE Term II Biology XI, , PART 2, Subjective Questions, l, , Short Answer (SA) Type Questions, 1. Draw labelled diagram of the neuron., , (NCERT), , Ans., Dendrites, Nissl’s granules, Cell body, , quick coordination provided by neural system is called, neural coordination. The mechanism of neural, coordination involves transmission of nerve impulse,, impulse conduction across a synapse and the physiology, of reflex action., , 5. How do the ionic gradients across the resting, membrane can be maintained?, , Nucleus, , Ans. The ionic gradients across the resting membrane are, , Schwann cell, , maintained by the active transport of ions by the, sodium-potassium pump., , Axon, , 6. State the role of sodium-potassium pump in the, , Myelin sheath, , maintenance of ionic gradients., , Node of Ranvier, , Ans. The sodium-potassium pump helps in the active transport, , of ions, 3 Na+ are transported outwards and 2K + inwards, through the neurolemma of neurons., , Axon terminal, Synaptic knob, , 2. What are the major differences between dendrites, and axons?, , 4. Write a short note on neural coordination. (NCERT), Ans.The organised network of point to point connection for, , (NCERT), , Ans. Differences between dendrites and axons are as follows, , Dendrites, , Axons, , These are short fibres, which branch, repeatedly and project, out of the cell body and, also contain Nissl's, granules., These fibres transmit, impulses toward the cell, body., Its branches terminate, into bulb-like synaptic, knobs., , The axon is a long branched fibre,, which terminates as a bulb-like, structure called synaptic knob. It, possesses synaptic vesicles, containing chemicals called, neurotransmitters., The axons transmit nerve, impulses away from the cell body, to a synapse., Their branches do not have, synaptic knobs., , 3. Differentiate between myelinated and, non-myelinated axons., (NCERT), Ans. Differences between myelinated and non-myelinated, axons are as follows, Myelinated Axons, , Non-myelinated Axons, , The myelinated nerve fibres, are enveloped with, Schwann cells, which form a, myelin sheath around the, axon., Myelinated nerve fibres are, found in spinal and cranial, nerves., , Non-myelinated nerve fibres, are enclosed by a Schwann, cells that do not form a, myelin sheath around the, axon., These are commonly found in, autonomous and the somatic, nervous systems., , 7. Compare resting potential and action potential., (NCERT), Ans. Comparison between resting and action potential is as, , follows, Resting Potential The electrical potential difference across, the plasma membrane is called the resting potential., Action Potential It is another name of nerve impulse. The, action potential is an electrical signal that travels along an, axon., , 8. Explain the factors on which the impulse, conduction depends., Ans. Impulse conduction depends upon, , (i) permeability of axolemma (axon membrane), (ii) osmotic equilibrium between the axoplasm and, extracellular fluid present outside the axon., , 9. Explain the role of Na + in the generation of action, potential., (NCERT), Ans. When a stimulus is applied to a nerve, the membrane of, the nerve becomes freely permeable to Na + . This leads to, a rapid influx of Na + followed by the reversal of the, polarity at that site, i.e. the outer surface of the membrane, becomes negatively charged and the inner side becomes, positively charged., The electrical potential difference across the plasma, membrane at the membrane is called the action potential,, which is in fact termed as a nerve impulse. Thus, this, shows that Na + ions play an important role in the, conduction of nerve impulse.

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154, , CBSE Term II Biology XI, , 10. Differentiate between conduction of impulse, through myelinated nerve fibre and non-myelinated, nerve fibre., , Ans. Differences between grey matter and white matter are as, , follows, Grey matter, , White matter, , fibre and non-myelinated nerve fibre are as follows, , It is made up of, non-myelinated nerve fibres., , It is made up of, myelinated nerve fibres., , Conduction in, Myelinated Nerve Fibre, , Conduction in, Non-myelinated Nerve Fibre, , It is grey in colour., , It is white in colour., , Depolarisation occurs only, in the nodes of Ranvier of, axon., , Depolarisation occurs all along, the length of the nerve fibre., , It forms the outer layer of brain, and inner layer of spinal cord., , It forms inner part of the, brain and outer part of, the spinal cord., , Transmission of nerve impulse is, slow., , Transmission of nerve, impulse is very fast., , Ans. Differences between conduction in myelinated nerve, , Action potential jumps from Action potential travels along, one node of Ranvier to, the entire length of the nerve, another., fibre., It is called saltatory, It is a slower conduction, conduction and is more fast. process., Lesser amount of energy, spent., , More amount of energy is, spent., , 11. Explain the significance of saltatory conduction., Ans. This process accounts for the greater speed of an impulse, , travelling along a myelinated neuron than along a, non-myelinated one. It is upto 50 times faster than the, non-myelinated nerve fibre., , 12. Nervous system and computers share certain, common features. Comment in five lines., (Hint: CPU, input-output devices). (NCERT Exemplar), Ans. The sensory neurons present in various organs sense the, , environment and extend the message to the brain. So, it is, equivalent to input device of computers., Brain acts as CPU, i.e. Central Processing Unit. The, information gathered by sensory neurons is processed by, brain and it gives command to the concerned organ to act, accordingly. This message is taken or conveyed by motor, neurons which act as output devices., , 13. Differentiate between piamater and duramater., Ans. Differences between piameter and duramater are as, , follows, , 15. Which nerve tract connects the right and left, hemispheres of the cerebrum? Name the four lobes, of hemisphere of brain., Ans. Right and left hemispheres of the cerebrum are, , connected by corpus callosum. Each hemisphere is, divided into frontal lobe, temporal lobe, parietal lobe and, occipital lobe., , 16. Differentiate between thalamus and hypothalamus., (NCERT), Ans. Differences between thalamus and hypothalamus are as, , follows, Thalamus, , Hypothalamus, , The cerebrum wraps around a It lies at the base of the, structural part of brain called thalamus., thalamus., All types of sensory input pass It contains neurosecretory, synapses to the thalamus., cells that secrete, hypothalamus hormones., It controls emotional and, memory functions., , It regulates, sexual behaviour, expression of emotional, reactions and motivation., , 17. Differentiate between cerebrum and cerebellum., (NCERT), Ans. Differences between cerebrum and cerebellum are as, , Piamater, , Duramater, , follows, , It is the inner most mening, around the brain., , It is the outer most mening, around the brain., , Cerebrum, , It is attached to the brain., , It is attached to the inner, surface of the cranium., , It is the most developed It is the second developed part of, part in brain., brain also called as little cerebrum., , It is attached to the brain at two It is free, not attached to, places to form choroid plexus., the choroid plexus., , 14. In nervous system how grey matter is different from, the white matter?, Or Explain grey matter and white matter., , Cerebellum, , Corpus callosum, connects two cerebral, hemispheres., , The two lateral hemispheres of, cerebellum are connected by, vermis., , Its functions are, intelligence, learning,, memory, speech, etc., , It contains centres for coordination, and error checking during motor, functions and cognition.

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155, , CBSE Term II Biology XI, , 18. If someone receives a blow on the back of neck,, what would be the effect on the person’s CNS?, (NCERT Exemplar), Ans. If a person receives a blow on the back, it results in an, , impairment of cognitive abilities or physical functioning., It can also result in the disturbance of behavioural or, emotional functioning. Cervical injuries often result in, quadriplegia (tetraplegia)., , The human brain is divisible into three main parts, (i) Forebrain The forebrain consists of, Olfactory Lobes The anterior part of the brain is formed, by a pair of short club-shaped structures, the olfactory, lobes. These are concerned with the sense of smell., Cerebrum It is the largest and most complex of all the, parts of the human brain. A deep cleft divides the, cerebrum longitudinally into two equal halves. These are, termed as the left and right cerebral hemispheres. These, hemispheres are connected by a large band of myelinated, fibres the corpus callosum., In each cerebral hemisphere, there are three types of, functional areas, Sensory Areas It receives impulses from the receptors, and motor areas transmit impulses to the effectors., , 19. Distinguish between cranial nerve and spinal nerve, in human., (NCERT), Ans. Differences between cranial nerve and spinal nerve in, human are given below, Cranial Nerve, , Spinal Nerve, , n, , The cranial nerves originate in, The spinal nerves originate, the brain and terminate mostly in in the spinal cord and extend, organs head and upper body., to parts of the body below, the head., There are 12 pairs of cranial, There are 31 pairs of spinal, nerves., nerves., Most of the cranial nerves contain All of the spinal nerves, axon of mixed, sensory and motor contain axons of mixed, neurons., neurons., l, , Long Answer (LA) Type Questions, 1. During resting potential, the axonal membrane is, polarised. Explain the movement of positive and, negative ions leading to polarisation., (NCERT Exemplar), , Ans. In a resting nerve fibre (a nerve fibre that is not, , conducting an impulse), the axoplasm (neuroplasm of, axon) inside the axon contains high concentration of K +, and negatively charged proteins and low concentration of, Na +., In contrast, the fluid outside axon contains a low, concentration of K + and a high concentration of Na + and, thus, forms a concentration gradient., These ionic gradients across the resting membrane are, maintained by the active transport of ions by the, sodium-potassium pump, which transports 3Na +, outwards and 2K + inwards (into the cell)., As a result, the outer surface of the axonal membrane, possesses a positive charge, while its inner surface, becomes negatively charged and therefore, is polarised., The electrical potential difference across the resting, plasma membrane is called as the resting potential. The, state of the resting membrane is called polarised state., , 2. What is brain? Also describe the components of, brain with their functions., Ans. The brain is the central information processing organ of, , our body and acts as the ‘command and control system’of, all body activities., The brain is the anteriormost part of the central neural, system, which is located in the cranium (cranial cavity) of, the skull., , Association Areas These are large regions that are, neither clearly sensory nor motor in junction. They, interpret the input, store the input and initiate a, response in light of similar past experience. Thus, these, areas are responsible for complex functions like, memory, learning, reasoning and other intersensory, associations., (ii) Midbrain The midbrain is located between the thalamus, (hypothalamus) of the forebrain and pons of the hindbrain., A canal called the cerebral aqueduct passes through the, midbrain., The dorsal portion of the midbrain mainly consists of two, pairs (i.e. four) of rounded swellings (lobes) called, corpora quadrigemina. Midbrain helps in the movement, of eyes, auditory and visual processing., (iii) Hindbrain The hindbrain consists of, n, , (a) Pons consists of fibre tracts that interconnect, different regions of the brain., (b) Cerebellum is the second largest part of the human, brain (means first being the cerebrum). It helps in, coordination and movement related to motor skills,, maintain posture and balance of body., (c) Medulla oblongata is connected to the spinal cord, and contains centres, which control respiratory, rhythm, cardiovascular reflexes, gastric secretions and, the postural gestures of the body (vertigo)., , 3. (i) Describe the protective coverings of the brain., (ii) Differentiate between sympathetic and, parasympathetic nerves., Ans., , (i) Brain is covered by three membranes or meninges, (cranial meninges), (a) The outermost membrane, the duramater is the, tough fibrous membrane adhering close to the, inner side of the skull., (b) The middle membrane, is very thin layer called, arachnoid membrane (arachnoid mater)., (c) The innermost membrane, the piamater is thin,, very delicate, which is in contact with the brain, tissue.

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156, , CBSE Term II Biology XI, , (ii) Differences between sympathetic and, parasympathetic nerves are are as follows, Sympathetic Nerves, , Parasympathetic Nerves, , Preganglionic fibres are, short and post-ganglionic, fibres are long., It releases sympathin or, nor-epinephrine., It increases the metabolic, rate., It accelerates activities, and prepares body against, adverse conditions for, flight or fright., , Preganglionic fibres are, long and post-ganglionic, fibres are short., It releases acetylcholine., It does not effect the, metabolic rate., It normalises accelerated, activities and provides, feeling of relation, comfort, and pleasure., , 4. (i) Differentiate between resting membrane potential, and action potential., (ii) What is the function of pons Varolii and where are, they located?, Ans., , (i) Differences between resting membrane potential and, action potential are as follows, Resting Potential, , Action Potential, , It is the electrical potential, difference across the plasma, membrane., Here sodium pump, operates., During this, outside of the, membrane is, electropositive, while inside, is electronegative., Membrane is more, permeable to K + ions than, Na + ions., , It is an electrical signal that, travels along an axon., , Ans. The urge of eating and drinking is controlled by, , hypothalamus in brain. It is a part of forebrain., , (ii) How does the action taken by Priya kept her awake?, Ans. Priya increased the number of sensory stimuli which, , were relayed to the cerebral cortex. Thus, it gets, activated and prevented sleeping or drowosiness., , (iii) How does the sensory and motor signals are, coordinated in human brain?, Ans. In the human brain, sensory and motor signals are, , coordinated by the thalamus of forebrain. It is present, between the cerebral cortex and midbrain., It mainly helps to relay motor and sensory signals to, cerebral cortex., , (iv) Emotional reactions are coordinated by complex, structures in brain. Explain., Ans. Emotional reactions like excitement, pleasure, fear, etc.,, , are controlled by the limbic system. It is a complex, structure which constitutes deep structure like, amygdala, hippocampus, etc., , (v) Mention the function of association areas in brain., Ans. Association areas are the mixed areas which are neither, , Here sodium pump does, not operate., During this outside of the, membrane is, electronegative, while, inside is electropositive., Membrane is more, permeable to Na + ions than, K + ions., , (ii) Pons Varolii forms the floor of brain stem and serves as, neuronal link between cerebral cortex and cerebellum., It consist of pontine nuclei, pneumotaxic area and, apneustic area. Pontine nuclei are sites at which, signals for voluntary movements are relayed into, cerebellum. Both pneumotaxic and apneustic area, control respiration., l, , (i) Which part of brain control the urge of eating and, drinking?, , Case Based Questions, 1. Direction Read the following passage and answer the, questions that follows., After a long day at work, Priya was driving back to, home by her car. As she was very tired, she begins to, feel drowosy and felt the urge to eat or drink, something at the same time. To keep herself awake,, she took a sip of cold water, opened the car windows, and increased the volume of the music system in her, car. In a short time, she begins to feel alert and, awake., , sensory nor motor in function. These perform complex, functions like memory and communication., , 2. Direction Read the following passage and answer, the questions that follows., A man is admitted to a hospital. He is suffering, from an abnormal low body temperature, loss of, appetite and extreme thirst. The doctor consoled, him and also prescribed brain scan as he, suspected, there would be a tumour in his brain., (i) Mention the reason behind the abnormalities of, the patient., Ans. The reason behind abnormalities of the patient is, , tumour in hypothalamus., , (ii) Which part of the brain would probably show a, tumour?, Ans. Hypothalamus probably show a tumour., , (iii) Identify the location of hypothalamus., Ans. The hypothalamus lies at the base of thalamus in the, , forebrain., , (iv) Give the name of the nervous tissues, which form, the spinal cord., Ans. Grey and white matter from the spinal cord., , (v) Which is the largest and most complex of all the, parts of the human brain?, Ans. Forebrain, which mainly includes cerebrum.

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Chapter Test, Multiple Choice Questions, , 1. Identify the basic function(s) of neural system., (a) Receiving sensory input from internal and external, environment by nerves, (b) Processing the input information, (c) Responding to stimuli, (d) All of the above, , 2. Identify the incorrect statement., (a) CNS is the site of information processing and control, (b) PNS comprises of all the nerves of the body associated, with CNS, (c) CNS includes brain and spinal cord, (d) PNS contains afferent fibres only, , 3. Dendrites of neurons are, (a) highly branched, short fibres containing Nissl’s granules, (b) unbranched, long process of cell body, (c) unbranched, short and do not contain cytoplasm, (d) branched, long process without cytoplasm, , 4. During the transmission of nerve impulse through a, nerve fibre, the potential on the inner side of the, plasma membrane has which type of electric charge?, (a) First positive, then negative and continue to be negative, (b) First negative, then positive and continue to be positive, (c) First positive, then negative and again back to positive, (d) First negative, then positive and again back to negative, , 5. Pons of the brain connects the, (a) two lobes of cerebellum, (b) cerebrum and cerebellum, (c) spinal cord with the brain, (d) two cerebral hemispheres, , (a) Both A and R are true and R is the correct explanation of A, (b) Both A and R are true, but R is not the correct explanation, of A, (c) A is true, but R is false, (d) A is false, but R is true, , 1. Assertion (A) The membrane of a neuron remains in, polarised state., Reason (R) Ion channels on the neural membrane are, selectively permeable to different ions., , 2. Assertion (A) The axoplasm inside the axon contains, high concentration of K+ and negatively charged, proteins., , Reason (R) The axonal membrane is impermeable to Na+, and negatively charged proteins., , 3. Assertion (A) Association area in cerebrum are sensory, in function., Reason (R) Association areas help to carry out complex, functions., , Short Answer Type Questions, , 1. Enlist the general functions of neural system in human, body., , 2. Give a brief account about the type of neurons found in, human body., , 3. State the functions of hypothalamus., 4. Briefly explain the structure of cerebral cortex with, reference to grey matter and white matter found in it., , 5. What functions are performed by the visceral nervous, system in human body? Explain briefly., , Assertion-Reasoning MCQs, Direction (Q. Nos. 1-3) Each of these questions contains, two statements, Assertion (A) and Reason (R). Each of, these questions also has four alternative choices, any, one of which is the correct answer. You have to select, one of the codes (a), (b), (c) and (d) given below., , Long Answer Type Questions, , 1. Explain the mechanism of generation of action potential, and how does it help in conduction of nerve impulse, through neurons., , 2. Discuss the somatic division of peripheral nervous, system in detail., , Answers, Multiple Choice Questions, 1. (d), , 2. (d), , 3. (a), , 4. (d), , Assertion-Reasoning MCQs, 1. (a), , 2. (b), , 3. (d), , 5. (a), , For Detailed Solutions, Scan the code

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158, , CBSE Term II Biology XI, , CHAPTER 10, , Chemical, Coordination, and Integration, In this Chapter..., l, , Endocrine Glands and Hormones, , l, , Human Endocrine System, , l, , Structure and Functions of Major Endocrine Glands, , l, , Mechanism of Hormone Action, , The neural coordination is rapid, but short-lived in nature., However, the nerve cells do not reach to each and every, cell of the body. So, a special kind of coordination and, integration is provided to each cell for continuous cellular, functions. This special function is performed by, hormones., Thus, the nervous system and endocrine system are, intimately related to each other forming neuroendocrine, system together that jointly coordinate together that, regulates the physiological functions of the body., , Endocrine Glands and, Hormones, The endocrine glands are ductless glands, i.e. lack ducts., They pour their secretion into the surrounding blood for, transport to the site of action or distantly located target, organ. Their secretions are called hormones or internal, secretion., , Hormones, These are non-nutrient chemicals, which are produced in, trace amounts and act as intercellular messengers. These, are responsible for regulating the biological processes in, the body. The organised endocrine glands also secrete a, number of new molecules in addition to the hormones., , Vertebrates have large number of chemicals acting as hormones, that provide coordination, while invertebrates possess very, simple endocrine system with few hormones., Note, , l, , l, , The first hormone was discovered by William M Bayliss and Ernest H, Starling in 1903., Endocrinology is the study of endocrine glands and hormones, secreted by them., , Human Endocrine System, The endocrine system in humans constitutes the endocrine, glands and hormone producing diffused tissues/cells located in, different parts of our body. In endocrine system, the hormone, from one gland may stimulate or inhibit another endocrine gland., These can also vary in structure., , Types of Human Endocrine Glands, The endocrine glands are of following two types in humans, (i) Pure Endocrine Glands, These entirely work for the secretion of hormones. They include, the hypothalamus, pituitary, pineal, thyroid, adrenal, pancreas,, parathyroid, thymus glands and gonads (i.e. testes in males and, ovaries in females)., (ii) Partial Endocrine Glands, These are partly endocrine and partly exocrine in function. They, include kidneys, gastrointestinal tract, heart and placenta, etc.

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159, , CBSE Term II Biology XI, , Hypothalamus, , These hormones finally reach the pituitary gland through a, portal circulatory system (hypophyseal portal system), thereby, regulating the functions of anterior pituitary., The posterior pituitary however, functions under the direct, regulation of the hypothalamus., , In humans, the complete endocrine system works more or, less under the influence of hypothalamus., , Pituitary Gland (Hypophysis), , Location, Hypothalamus is located in the basal part of diencephalon, (forebrain) and it regulates a wide spectrum of functions in, the body., , It is the smallest endocrine gland, but serves very important, role in the human endocrine system. It directly or indirectly, controls almost all other endocrine glands of the body. It is, also known as master gland., , Structure and Functions of, Major Endocrine Glands, , Origin, It develops from the ectoderm of embryo like other parts of, brain., Structure, It is composed of nervous tissue. It connects with the, anterior lobe of pituitary by hypophyseal portal blood vessels, and to the posterior lobe of pituitary by the axons of its, neurons., Hormones, Hypothalamus contains several groups of neurosecretory, cells, known as nuclei, which produce hormones. The, function of these hormones is to regulate the synthesis and, secretion of pituitary hormones., Hormones produced by hypothalamus are of following, two types, (i) Releasing Hormones, , Origin, It originates from the ectoderm of the embryonic germ, layers., Location and Structure, It is reddish grey in colour and is roughly oval in shape. It is, about a size of a pea seed. The pituitary gland is located in a, small bony cavity of the brain called sella turcica., Hormones, The pituitary gland has three major lobes, i.e. anterior,, intermediate and posterior lobe. It is anatomically divided, into two major portions., Parts of, Pituitary Gland, , Hormones, , Functions, , 1. Adenohypophysis, Pars distalis, , Growth, Hormone (GH), , These are the hormones that stimulate the secretion of, pituitary hormones, e.g. Gonadotropin Releasing Hormone, (GnRH), which stimulates the gonadotroph cells of anterior, pituitary gland to release gonadotropins., , l, , l, , l, , l, , (ii) Inhibiting Hormones, , These are the hormones that inhibit the release of pituitary, hormones, e.g. somatostatin, which inhibits the secretion of, growth hormone from anterior lobe of pituitary gland. All, these hormones originating in the hypothalamic neurons, pass, through the axons and are released from their nerve endings., Hypothalamus, Hypothalamic neurons, , Portal circulation, , Prolactin (PRL) Stimulates the growth of, mammary glands, lactation, and maintenance of corpus, luteum., Synthesis and secretion of, Thyroid, thyroid hormones T3 and, Stimulating, Hormone (TSH) T4 from thyroid gland., Adrenocorticot- Synthesis and secretion of, ropic Hormone glucocorticoids from the, (ACTH), adrenal cortex., Luteinizing, Hormone (LH), , l, , Posterior pituitary, Anterior pituitary, , Diagrammatic representation of, pituitary and its relationship with hypothalamus, , Stimulates body growth., Hyposecretion causes, dwarfism, i.e. stunted, growth., Hypersecretion causes, gigantism., Excess secretion of GH, in adults causes, acromegaly., , l, , In males, stimulates the, synthesis and secretion, of androgens from, testes., In females, induces, ovulation and maintains, corpus luteum.

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160, Parts of, Pituitary Gland, , CBSE Term II Biology XI, , Hormones, , Follicle, Stimulating, Hormone (FSH), , Functions, l, , l, , Pars intermedia, , Melanocyte, Stimulating, Hormone, (MSH), , 2. Neurohypophysis Oxytocin, (Pars nervosa), , l, , l, , l, , l, , Vasopressin, (Anti-Diuretic, Hormone or, ADH), , l, , l, , In males, FSH and, androgens regulate, spermatogenesis., In females, stimulates, the growth and, development of, ovarian follicles., Acts on melanocytes, and regulates skin, pigmentation., Hypersecretion causes, hyperpigmentation., Acts on the smooth, muscles and, stimulates their, contraction during, childbirth., Stimulates milk, ejection from the, mammary glands., Acts mainly at kidneys, and helps in H 2O and, electrolytes resorption, and prevents diuresis., Hyposecretion causes, diabetes insipidus., , Pineal Gland (Epiphysis), It is a small gland in the brain derived from the embryonic, ectoderm., Location, It is located on the dorsal side of the forebrain between the, cerebral hemispheres., Structure, Pineal is a very small gland reddish grey in colour, vascular, conical in shape and has solid body. It is composed of pineal, cells and supporting glial cells., Hormones, It secretes a hormone called melatonin that plays a very, important role in the regulation of a 24 hrs (diurnal) rhythm, of our body and melatonin also helps in maintaining the, normal rhythms of sleep-wake cycle, body temperature., Metabolism, pigmentation, menstrual cycle as well as our, defence capability is also influenced by this hormone., , Thyroid Gland, The thyroid gland is known to be the largest endocrine gland., Origin, It is endodermal in origin, i.e. originates from the endoderm of, the embryo. The thyroid gland is bilobed, highly vascular organ., Location and Structure, It surrounds the front of the larynx and is composed of two, lobes. Each of its lobe is located on either side of the trachea in, the neck interconnected with each other through a thin flap of, connective tissue called isthmus., Vocal cord, , Thyroid gland, Trachea, , Diagrammatic view of the position of thyroid gland (ventral side), , It is composed of follicles (round in shape) held together by, loose connective tissue called stromal tissues. Each thyroid, follicle is composed of follicular cells, enclosing a cavity., Hormones, The follicular cells synthesise following two hormones, (i) Tetraiodothyronine or thyroxine ( T4 ) hormone, (ii) Triiodothyronine ( T3 ) hormone, Both these hormones are iodinated forms of the amino acid, (tyrosine). They are stored in the colloid that fills the follicles, and are released to the blood when needed. Iodine (in diet) is, essential for the synthesis of hormone at normal rate in thyroid., , Disorders, (i) Hypothyroidism, , This disorder occurs due to the deficiency of iodine in our diet., It leads to the enlargement of thyroid gland commonly known as, goitre., (a) Hypothyroidism in women at the time of pregnancy, affects the development and maturation of the growing, baby and leads to stunted growth (cretinism), mental, retardation, low intelligence quotient, abnormal skin,, deaf-mutism, etc., (b) Hypothyroidism in adult women may cause irregular, menstrual cycle.

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161, , CBSE Term II Biology XI, , (ii) Hyperthyroidism, , It is the condition during which rate of synthesis and, secretion of thyroid hormones is increased to abnormal, high levels. It may occur due to the cancer of the thyroid, gland or due to development of nodules of the thyroid, gland. It adversely affects the body physiology of an organism., Exophthalmic Goitre (Graves’ disease) In this, enlargement, of thyroid gland takes place. Thus, thyroid secretion, increases. It leads to protrusion of the eyeballs, increased, basal metabolic rate and weight loss., , l, , l, , l, , Hashimoto disease An autoimmune disorder in which the, thyroid gland is destroyed by autoimmunity. All the functions of, thyroid gland gets impaired during this disease., , l, , Myxoedema It is caused by deficiency of thyroid hormones in, adults, it is more common in women and is characterised by puffy, appearance due to the accumulation of fat in subcutaneous tissue, because of low metabolic rate and retarded oxidation., , Hormones, Parathyroid glands secrete a single hormone known as, parathormone or Parathyroid Hormone or PTH (functions, opposite to the thyrocalcitonin hormone). The secretion of, PTH is regulated by the circulating level of calcium ions in, the blood., Functions of Parathyroid Hormone, Parathyroid hormone serves several functions in the body,, such as, (i) It increases the level of Ca 2+ in the blood., (ii) It stimulates the process of bone reabsorption, (i.e. dissolution/demineralisation) by acting on bones., (iii) It also stimulates reabsorption of Ca 2+ by the renal, tubules and absorption of Ca 2+ from the digested food., Parathyroid glands, , Functions of Thyroid Hormones, Thyroid hormones serves several functions in the, body, such as, (i) These hormones regulate and maintain the Basal, Metabolic Rate (BMR), i.e. both T3 and T4 hormones, increase the overall metabolic rate of the body., (ii) They support the process of formation of red blood, cells. Also help in controlling the metabolism of, carbohydrates, proteins and fats., (iii) Influences the maintenance of water and electrolyte in, our body. Apart from the hormone T3 and T4 , thyroid, gland also secretes a protein hormone called, Thyrocalcitonin (TCT). Its main function is to regulate, the level of calcium in blood., , Parathyroid Gland, These are small glands in the human neck that produces, parathyroid hormone., Origin, It is endodermal in origin., Location, These glands are situated on the posterior side of the thyroid, gland., , Diagrammatic view of the position of parathyroid gland (dorsal side), , By the above mentioned functions of parathyroid hormone, it, is clear that PTH acts as a hypercalcemic hormone (increases, the level of Ca 2+ in the blood). Parathyroids are under the, feedback control of blood calcium level. A fall in Ca 2+ in, blood stimulates them to secrete PTH. Thus, both the, hormones (TCT and PTH) play a significant role to control, and regulate the concentration of Ca 2+ and phosphorus., , Adrenal Glands (Suprarenals), Location, Our body has a pair of adrenal glands. Each located at the, anterior part of each kidney., Adrenal cortex, Adrenal gland, Fat, Adrenal medulla, , Structure, Parathyroid glands are four in number, i.e. each pair is, situated in the two lobes of the thyroid gland on either side., These are small, flat and oval gland., , Kidney, (a), , (b), , Diagrammatic representation of adrenal gland

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162, , CBSE Term II Biology XI, , Structure, , (c) Sexocorticoids (Androgen), , Adrenal glands are conical yellowish bodies composed of, two types of tissues., These are as follows, , Adrenal cortex also produces a small quantity of androgenic, steroids, i.e. sex hormone (androgens) both in males and, females. These hormones are secreted as DHEA (Dehydroxy, Epiandrosterone), which acts as a precursor of both testosterone, and oestrogen., , 1. Adrenal Cortex, It is an external firm, pale-yellowish tissue derived from, mesoderm of embryo., It is further divided into three concentric layers, (i) Zona Reticularis It is the inner layer of the cortex, whose cells are arranged in the net-like fashion., (ii) Zona Fasciculata It is the middle layer of the cortex., It is the widest of all three layers., (iii) Zona Glomerulosa It is the outermost layer. It is, composed of five layers of compactly arranged cells., Hormones secreted by these three layers of adrenal cortex, are collectively known as corticoids., Three groups of steroid hormones are secreted by adrenal, cortex, such as, , Functions of Sexocorticoids, , (a) Mineralocorticoids (Aldosterone), , 2. Adrenal Medulla, , They regulate the balance of water and electrolytes in our, body. Aldosterone is the major mineralocorticoid found in, our body. It mainly acts on renal tubules stimulating the, reabsorption of Na + and water. Also stimulates the, excretion of K + and phosphate ions from the body., Functions of Mineralocorticoids, , Its main function is in maintaining electrolytes, body fluid, volume, osmotic pressure and blood pressure of the body., (b) Glucocorticoids (Cortisol), , (i) It plays a major role in the growth of axial, pubic and, facial hair during puberty in humans., (ii) Development of acne are also due to these hormones in, young girls., (iii) It also plays an important role in the development of, embryo (foetus)., Cushing’s syndrome is due to excess of cortisol, while an excess of, aldosterone leads to aldosteronism., , l, , Adrenal virilism is caused by excess of sex corticoids in a female., In this, there is development of male secondary sexual characters, such as beard, moustaches, etc., in females., , Activation of Adrenaline and Nor-adrenaline, l, , l, , (i) Cortisol stimulates the liver for the synthesis of, carbohydrates from non-carbohydrate sources, (like amino acids and glycerol). This process is known, as gluconeogenesis. Hence, glucocorticoids stimulate, gluconeogenesis, lipolysis and proteolysis., (ii) Inhibition of cellular uptake and utilisation of amino, acids., (iii) Cortisol is involved in the maintenance of, cardiovascular system and in proper functioning of, kidney., (iv) Cortisol produces anti-inflammatory reactions and, also functions in suppression of immune response., (v) It stimulates the production of RBC., , Addison’s disease is caused by deficiency of mineralocorticoids., , l, , The adrenal medulla lies in the centre of the adrenal gland. It is, an internal soft, dark reddish brown tissue derived from the, ectoderm., The adrenal medulla secretes two hormones, (i) Adrenaline (epinephrine), (ii) Nor-adrenaline (nor-epinephrine), , These are the hormones, which regulate the metabolism of, carbohydrates, proteins and fats. Cortisol is the main, glucocorticoid found in our body., Functions of Glucocorticoids, , l, , Both hormones belong to the category of compounds known, as catecholamines and are secreted in response to any kind, of stress, danger and during emergency situations like, increased respiratory rate, heartbeat, etc., The CNS at the time of stress or danger stimulates the, adrenal medulla to release both these hormones. These are, also known as emergency hormones or hormones of fight or, flight., , Functions of Adrenaline and Nor-adrenaline, , These hormones serve following purposes, (i) Increase alertness., (ii) Dilation of pupil., (iii) Piloerection (raising of hairs of hands and legs)., (iv) Increase in heartbeat and rate of respiration., (v) They also stimulate the breakdown of glycogen due to, which the concentration of glucose increases in the, blood., (vi) Stimulate breakdown of lipids and proteins.

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163, , CBSE Term II Biology XI, , Pancreas, , (ii) Insulin, , It is a composite gland that acts as both exocrine and, endocrine gland. Such glands are also called heterocrine, gland., , l, , Origin, It originates from the endoderm of the embryonic germ layers., , This peptide hormone plays a major role in regulation of, glucose level in the blood. It mainly acts on hepatocytes, and adipocytes (cells of adipose tissue), increasing the, cellular glucose uptake and utilisation., As a result, the movement of glucose takes place rapidly, from blood to liver cells and cells of adipose tissues by, decreasing the blood glucose level (hypoglycemia)., , l, , Location, It lies below the stomach, in the loop of duodenum., Structure, It is elongated yellowish gland that consists of large, number of acini and ducts. Besides these, pancreas consists, of 1-2 millions of small group of specialised cells, called, Islets of Langerhans (after the name of their discoverer, Paul Langerhans in 1869)., In normal human pancreas, these cells represent only 1-2%, of the pancreatic tissue., Each islet consists of major two types of cells as, (i) α-cells (about 25%) It secretes a peptide hormone, called glucagon., (ii) β-cells (about 60%) It secretes another peptide, hormone called insulin., , Deficiency Disorder of Insulin, l, , Diabetes mellitus is the common complex disorder caused due to, prolonged hyperglycemia., , l, , This is associated with the loss of glucose (when complete glucose, cannot be reabsorbed by the kidneys) in the urine as pancreas, fails to release adequate amount of insulin to lower the level of, glucose in the body., , l, , During this disorder, cells fail to utilise glucose and other, carbohydrate for production of energy instead start utilising, proteins and fats for it (due to which person becomes weak)., Diabetic patients are successfully treated with insulin therapy., , l, , l, , Note Apart from α and β-cells, Islets of Langerhans consist of two or, more types of cells called delta cells or D-cells (about 10%), which secrete somatostatin hormone and PP-cells or F-cells, (which secrete Pancreatic Polypeptide-PP hormone)., , Hormones, Glucagon and insulin have antagonistic effect on blood, glucose level. This can be cleared from the functioning given, below, (i) Glucagon, , This peptide hormone plays an important role in maintaining, the normal blood glucose levels. It brings about change of liver, glycogen to blood glucose., Functions of Glucagon, , This hormone serves following functions, (a) It acts mainly on liver cells (hepatocytes) and stimulates, glycogenolysis, which results in an increased blood, sugar known as hyperglycemia., (b) Apart from this, glucagon also stimulates the process of, gluconeogenesis which also contributes to, hyperglycemia. Glucagon is known as hyperglycemic, hormone because it reduces the cellular glucose uptake, and utilisation., (c) It reduces glycogenesis and also enhances lipolysis., Note Glucagon also stimulates the secretion of insulin from beta cells, by its paracrine effect., , Functions of Insulin, This hormone serves following functions, (a) Insulin stimulates the conversion of glucose to, glycogen (glycogenesis) in the target cells., (b) Decreases gluconeogenesis., (c) Decreases glycogenolysis., (d) Also reduces the catabolism of proteins and fats., (e) Increases synthesis of fat in the adipose tissue from, fatty acids., , Testes, These are the primary sex organ of males. They perform dual, role, i.e. function as endocrine gland apart from acting as, male sex organ., Location, A pair of testis is located in the scrotal sac (outside abdomen), of male individuals., Structure, A testis is composed of many seminiferous tubules which are, lined by germinal epithelium and stromal or interstitial, tissue., This epithelium consists of three types of cells, (i) Follicular cells give rise to sperms., (ii) Interstitial cells or Leydig cells secrete group of, hormones called androgens mainly testosterone., (iii) Sertoli cells provide nourishment to sperms and also, secrete hormone (inhibin).

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164, Hormones, , Interstitial cells present in the intertubular spaces produce a, group of hormones, i.e. androgens. These include, testosterone, dihydrotestosterone and androstenedione.But, mainly secretes testosterone., Functions, , Androgen (mainly testosterone) performs a variety of, functions given below, (a) It regulates the development, maturation and functions, of male accessory sex organs like epididymis, vas, deferens, seminal vesicles, prostate gland, urethra, etc., (b) These hormones also stimulate changes associated with, puberty in males, i.e. muscular growth, growth of facial, and axillary hair, aggressiveness, low pitch of voice, etc., (c) Also stimulates the process of spermatogenesis, i.e., formation of spermatozoa., (d) Promotes the growth of body tissues such as bones and, muscles and helps in the formation of musculine body., (e ) Also have anabolic effects (synthetic effects) on the, metabolism of protein and carbohydrate., , CBSE Term II Biology XI, , (d) Plays a role in the development of growing ovarian, follicles., (e) Appearance of female secondary sex characters (deposit, of fat on thigh and hip region, high pitch, etc)., Progesterone, , (a) It is secreted in very high amount continuously during, pregnancy (i.e. supports pregnancy by forming placenta, and preventing contractions in uterine wall)., (b) It also acts on mammary glands and stimulates the, formation of alveoli (sac-like structures that store milk), and milk secretion., (c) It also helps in forming a mucus plug at cervix., Note Relaxin is another hormone secreted by ovary in the later stages of, pregnancy. Its main role is in softening ligament, widening pelvic, cavity, also affects other ligaments such as of foot, etc. Due to, which women may experience increase in their foot size during, pregnancy., , Mechanism of Hormone Action, , These are the primary sex organ in females that serve to, produce ova (female gametes) and female sex hormones., , Hormones are released from their respective gland in very, small amount. They carryout widespread effects in the body, of an individual. Their response is very specific and accurate., Their effects are produced on target tissues by binding to the, specific proteins known as hormone receptors, located in the, target tissues only., , Location, , Types of Hormones, , A pair of ovaries is located in the pelvic cavity (in the, abdomen)., , On the basis of the chemical nature, hormones are divided, into following four groups, (i) Peptide, Polypeptide, Protein Hormones (e.g. insulin,, glucagon, pituitary hormones, hypothalamic hormones,, etc)., (ii) Steroids (e.g. cortisol, testosterone, oestradiol and, progesterone)., (iii) Iodothyronines (e.g. thyroid hormones)., (iv) Amino acid derivatives (e.g. epinephrine)., , Ovaries, , Structure, It is an almond-shaped structure. Internally, it is composed of, ovarian follicles and stromal tissues., Hormones, Ovary produces two groups of steroid hormones,, i.e. oestrogen and progesterone. Oestrogens are secreted by, granulosa cells of Graafian follicle. After ovulation, the, ruptured follicle is converted to another structure called, corpus luteum, responsible for secretion of progesterone., Functions, , Both oestrogen and progesterone play a vital role in various, processes in female., These are as follows, Oestrogen, , (a) It helps in the growth of uterine endometrium layer, during each menstrual cycle., (b) It directly influences the development of mammary, glands., (c) Regulates female sexual behaviour and stimulates, growth and activities of female secondary sex organs., , Types of Hormone Receptors, Hormone receptors are of following two types, (i) Membrane Bound Receptors Hormone receptors, present on the cell membrane of the target cells., (ii) Intracellular Receptors Hormone receptors present, inside the target cell, e.g. nuclear receptor (present in, the nucleus of a cell)., Hormone-Receptor Complex, Binding of a hormone to receptor leads to the formation of a, hormone-receptor complex. Formation of this complex leads to, certain biochemical reactions or changes in the respective target, tissue. Metabolism of target tissue and their physiological function, are thus, regulated by hormones.

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165, , CBSE Term II Biology XI, , Hormones that interact with the membrane bound receptors do, not enter their target cell in normal condition, but generate, secondary messengers such as cyclic AMP (cAMP), IP3 , Ca 2+ ,, etc., which regulate cellular metabolism of the body, e.g. protein, or peptide hormone., Note Hormones do not participate in a metabolic reaction themselves,, they instead act as messengers only, i.e. mainly primary, messengers., , Functioning of Peptide Hormone, Protein hormone is water soluble in nature, binds to the extrinsic, receptors (present on cell surface) to form the hormone-receptor, complex. The formation of this complex causes the release of, enzyme, adenylate cyclase. This activated enzyme, thus leads to, the formation of cAMP (i.e. cyclic adenosine monophosphate), from ATP in the cell from the receptor site., , chromosome function by interaction of hormone-receptor, complex with the genome, e.g. steroid hormone,, iodothyronines, etc., Functioning of Steroid Hormone, Steroid hormones are lipid soluble in nature, so they can, easily diffuse through the cell membrane and bind to, receptor molecules present in the cytoplasm to form a, hormone-receptor complex that enters the nucleus., In nucleus, they bind to specific intracellular receptor site on, chromosomes and regulate gene expression that results in, physiological responses., Thus, the cumulative biochemical actions result in, physiological and developmental effects., , (e H, .g or, .o m, es on, tro e, ge, n), , Action of Hormone Through, Extracellular Receptor, , Activated, , ATP → cAMP + PPi, adenyl cyclase + Mg 2+, , The hormone receptor complex changes the permeability of the, cell membrane to facilitate the passage of materials through it, (and thereby, regulates cellular activities of the cell causing, specific response to occur)., , mRNA, , Hormone (e.g. FSH), Receptor, , Formation of hormone, receptor complex, , Ovarian cell membrane, t, Hormone-receptor, complex, , Response I, , Mechanism of hormone action : Steroid hormone, , ⇒, , Generation of second messenger, 2, (cyclic AMP or Ca +), ⇒, , Biochemical response, ⇒, , Physiological response, (ovarian growth), , Antagonistic and Synergistic Interactions, of Hormones, l, , Hormones can show both antagonistic and synergistic, interactions with each other. In antagonistic interactions, effects, of two hormones are opposite to each other on the target cells., For example, insulin and glucagon hormones, act, antagonistically on blood glucose level., , l, , In synergistic interaction, two or more hormones tend to, complement each other for their effect on target cells. For, example, oestrogen, progesterone, oxytocin, prolactin all acts, synergistically for the secretion, production and ejection of milk, in mammary glands., , Diagrammatic representation of the mechanism of hormone action of, peptide or protein hormone, , Action of Hormone Through, Intracellular Receptors, Hormones that interact with intracellular receptors are, mostly involved in the regulation of gene expression or

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166, , CBSE Term II Biology XI, , Chapter, Practice, PART 1, Objective Questions, l, , Multiple Choice Questions, 1. Endocrine glands, (a) do not possess ducts, (b) sometimes do not have ducts, (c) pour their secretion into blood through ducts, (d) always have ducts, (a) The endocrine glands are ductless glands that, secrete chemical messengers (called hormones)., , 2. Which of the following statements is correct in, relation to the endocrine system?, (a) Organs in the body like gastrointestinal tract, heart,, kidney and liver do not produce any hormones, (b) Non-nutrient chemicals produced by the body in, trace amount that act as intercellular messenger are, known as hormones, (c) Releasing and inhibitory hormones are produced by, the pituitary gland, (d) Adenohypophysis is under direct neural regulation, of the hypothalamus, (b) Statement in option (b) is correct in relation to the, endocrine system whereas the other statements are, incorrect., , 3. GnRH, a hypothalamic hormone, needed in, , reproduction, acts on, (a) anterior pituitary gland and stimulates secretion of, LH and oxytocin, (b) anterior pituitary gland and stimulates secretion of, LH and FSH, (c) posterior pituitary gland and stimulates secretion of, oxytocin and FSH, (d) posterior pituitary gland and stimulates secretion, of LH and relaxin, (b) GnRH is a hypothalamic hormone. It stimulates, the anterior lobe of pituitary gland to secrete LH and, FSH, which in turn stimulates the gonadal activity., , 4. Choose the correct statement about, ‘neurohypophysis’., (a) It stores the hormones produced by adenohypophysis, (b) It is poorly developed and functionless in humans, (c) It stores and releases hormones secreted by hypothalamus, (d) It secretes its own hormones, (c) Statement in option (c) is correct., , 5. Gigantism and dwarfism are the diseases related to, (a) prolactin hormone of mammary gland, (b) growth hormone of adenohypophysis, (c) luteinizing hormone of pituitary gland, (d) thyroid stimulating hormone of thyroid, (b) Gigantism and dwarfism are diseases related to growth, hormone., , 6. Select the incorrect statement., (a) The thyroid gland plays a negligible role in the regulation, of the basal metabolic rate, (b) The thyroid gland secretes thyroxine (T4 ) and, triiodothyronine ( T3 ), (c) The lobes of thyroid gland are interconnected with a thin, flap of connective tissue called isthmus, (d) The thyroid gland is composed of two lobes which are, located on either side of the trachea, (a) Statement in option (a) is incorrect and can be corrected, as, The thyroid gland plays an important role in the regulation of, the basal metabolic rate., Rest of the statements are correct., , 7. Choose the statements which correctly indicates the, functioning of thyroid hormones., I. Regulation of the basal metabolic rate., II. Stimulate the process of RBCs formation., III. Regulating the blood phosphorus levels., IV. Maintenance of pH and lipids balance.

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167, , CBSE Term II Biology XI, , The correct option is, , 10. Match the following columns., , (a) I, II and IV, (b) I and II, (c) I, II, III and IV, (d) III and IV, (b) Statements I and II are correctly indicate the, functioning of thyroid hormones. Statements III and, IV are incorrect and can be corrected as, l, , l, , Thyroid hormone regulates the blood calcium levels., Thyroid hormone maintains the balance of water and, electrolytes., , Column I, (Hormones of adrenal gland), A., , Mineralocorticoids, (Aldosterone), , 1., , Suppresses immune, response, , B., , Cortisol, , 2., , Growth of pubic hair, and axial hair during, puberty, , C., , Androgenic steroids of 3., adrenal cortex, , Increased blood glucose, concentration, , D, , Catecholamine, , Regulates balance of, H 2O and electrolytes, , 8. Identify A, B, C and D in the given diagrams and, , choose the correct combination., , C, , D, B, , (a) A–Thyroid, B–Trachea, C–Vocal cord,, D–Parathyroid glands, (b) A–Trachea, B–Thyroid, C–Vocal cord,, D–Parathyroid glands, (c) A–Trachea, B–Vocal cord, C–Thyroid,, D–Parathyroid glands, (d) A–Parathyroid glands, B–Thyroid, C–Vocal cord,, D–Trachea, (a) A–Thyroid, B–Trachea, C–Vocal cord,, D–Parathyroid glands, , 9. Consider the following statements with respect, to parathyroid gland., I. It regulates calcium and phosphate level in, blood., II. It elevates blood calcium level in children., III. It inhibits bone dissolution., IV. It has no role in bone formation., Choose the option containing incorrect, statements., (a) I and III, (b) II and V, (c) III and IV, (d) I and IV, (c) Statements III and IV are incorrect about, parathyroid gland and can be corrected as, , l, , Codes, A B C D, (a) 3 4 1 2, (c) 4 1 2 3, (c) A–4, B–1, C–2, D–3, , 4., , A B C D, (b) 2 3 4 1, (d) 1 2 3 4, , 11. Which of the following represents the action of, , A, , l, , Column II, (Functions), , It starts bone dissolution (osteoclastic action) and, stimulates excretion of calcium in blood., It affects the formation and growth of bones, membrane, permeability, nerve functioning and muscular activity of, body., , Rest statements are correct., , insulin?, (a) Increases blood glucose levels by hydrolysis of glycogen, (b) Increases blood glucose levels by stimulating glucagon, production, (c) Decreases blood glucose levels by forming glycogen, (d) Increases blood glucose level by promoting cellular, uptake of glucose, (c) Insulin plays a major role in the regulation of glucose, homeostasis. Insulin also stimulates conversion of glucose to, glycogen (glycogenesis) in the target cells and thus,, decreases blood glucose level., , 12. Given below are endocrine glands and their, characteristics., I. Testes – Present in scrotal sac, II. Ovary – Present outside abdominal cavity, III. Placenta – Produce hormones during pregnancy, Choose the option containing incorrectly matched, pairs., (a) I and II, , (b) II and III, , (c) Only II, , (d) Only III, , (c) Pair II in option (c) is incorrectly matched and can be, corrected as, Females have a pair of ovaries located inside the abdomen., Ovary is the primary female sex organ., Rest others are correctly matched endocrine glands and, their characteristics., , 13. The activity of formation of milk and the ejection of, milk is controlled by, (a) oxytocin and prolactin, respectively, (b) prolactin and oxytocin, respectively, (c) prolactin and prolactin, respectively, (d) oxytocin and oxytocin, respectively, (b) Prolactin regulates the growth of the mammary glands, and formation of milk. Oxytocin stimulates contraction of, uterus and milk ejection.

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168, , CBSE Term II Biology XI, , 1. Assertion (A) GnRH stimulates the pituitary, , 14. Match the following columns., Column I, (Types), , Column II, (Examples), , A., , Protein hormones, , 1., , Epinephrine, , B., , Steroid hormones, , 2., , Testosterone, progesterone, , C., , Iodothyronines, hormones, , 3., , Thyroid hormone, , D. Amino acid derivative 4., hormones, , Insulin and glucagon, , Codes, A B C D, (a) 1 2 3 4, (b) 4 3 2 1, (c) 4 2 3 1, (d) 4 2 1 3, (c) A–4, B–2, C–3, D–1, , (a) Both A and R are true and R is the correct, explanation of A., The hypothalamic hormones regulate the synthesis and, secretion of pituitary hormones. Like GnRH, (Gonadotropin Releasing Hormone) is released into the, pituitary through a portal circulating system where it, causes the anterior pituitary to release hormones like LH, and FSH. These two hormones stimulate gonadal activity, and hence called gonadotropins., , 2. Assertion (A) In old persons, there is gradually, , weakening of immune system., Reason (R) It is because of degeneration of, thymus gland., , 15. Identify A, B and C in the diagrammatic, , representation of the mechanism of hormone action., A, B, , Response 1, C, Physiological responses, , Select the correct option from the following., (a) A – Steroid hormone, B–Hormone-receptor complex,, C – Protein, (b) A–Protein hormone, B–Receptor, C–Cyclic AMP, (c) A – Steroid hormone, B–Receptor, C–Second, messenger, (d) A – Protein hormone, B – Cyclic AMP,, C – Hormone-receptor complex, (b) A – Protein hormone, B –Receptor, C–Cyclic AMP, l, , synthesis and release of gonadotropins., Reason (R) Hypothalamic hormones regulate the, synthesis and secretion of pituitary hormones., , Assertion-Reasoning MCQs, Direction (Q. Nos. 1-5) Each of these questions contains, two statements, Assertion (A) and Reason (R). Each of, these questions also has four alternative choices, any one, of which is the correct answer. You have to select one of the, codes (a), (b), (c) and (d) given below., (a) Both A and R are true and R is the correct, explanation of A, (b) Both A and R are true, but R is not the correct, explanation of A, (c) A is true, but R is false, (d) A is false, but R is true, , (a) Both A and R are true and R is the correct, explanation of A., In old persons, there is gradually weakening of immune, system because of degeneration of thymus gland., Thymus secretes a hormone named thymosin which, stimulates the development of certain kinds of WBCs, involved in generating immunity. It is prominent at the, time of birth, but it gradually atrophies in adults and its, disappearance causes ageing., , 3. Assertion (A) Our body secretes adrenaline in, , intense cold., Reason (R) Adrenaline raises metabolic rate., (a) Both A and R are true and R is the correct, explanation of A., Adrenaline is secreted in our body during cold, which, raises metabolic rate. It causes vasoconstriction of, essentially all the blood vessels of the body and increased, activity of the heart which prevents heat loss. Shivering, which is a rhythmic contraction of skeletal muscles, produces heat. Adrenaline, nor-adrenaline, etc., increase, the metabolic rate by stimulating the breakdown of fats., , 4. Assertion (A) Glucagon is a steroid hormone., , Reason (R) Glucagon is hyperglycemic hormone., (d) A is false, but R is true because, Glucagon is a peptide hormone, which plays an, important role in maintaining the normal blood glucose, level. This hormone stimulates the process of, gluconeogenesis and reduces the cellular glucose uptake, and utilisation., Thus, glucagon is hyperglycemic hormone., , 5. Assertion (A) Hormones interacting with, , membrane bound receptors normally do not enter, the target cells., Reason (R) They generate second messengers like, cyclic AMP, IP 3 and Ca 2+ .

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169, , CBSE Term II Biology XI, , (a) Both A and R are true and R is the correct explanation, of A., Hormones interacting with membrane bound receptors, normally do not enter the target cells because they, generate second messengers like cyclic AMP, IP 3 , Ca 2+ ,, etc. These are responsible for the amplification of signal., The hormone is called first messenger and cAMP is, termed as second messenger., l, , Case Based MCQ, 1. Direction Read the following passage and answer, the questions that follows., At the age of 5, Kabir was diagnosed with an, autoimmune disease, named diabetes mellitus. The, doctors advised Kabir’s parents to monitor Kabir’s, sugar level regularly and to give him insulin, injections regularly. Doctor also counsel the parents, about the importance of insulin in our body., (i) Insulin is a ............. hormone., (a) steroid, (b) proteinaceous, (c) amine, (d) amino acid derivative, (b) Insulin is a proteinaceous hormone. It is water soluble, and binds to the surface receptors of the cell., , PART 2, Subjective Questions, l, , Short Answer (SA) Type Questions, 1. Define the following, (i) Exocrine gland, (iii) Hormones, , (ii) Insulin is secreted by, (a) pituitary gland, (b) adrenal gland, (c) pancreas, (d) thyroid gland, (c) Insulin is secreted by the β-cells of the islets of, Langerhans (pancreas). It is a heterocrine gland., , (iii) Which hormone acts antagonistic to insulin?, (a) Oxytocin, (b) Prolactin, (c) Vasopressin, (d) Glucagon, (d) Glucagon acts antagonistic to insulin hormone. Insulin, decreases sugar level whereas glucagon increases it., , (iv) In the absence of insulin in body,, (a) blood glucose level decreases, (b) bone dissolution increases, (c) blood glucose level increases, (d) growth is inhibited, (c) If the level of insulin hormone decreases in body the, glucose would not be utilised by the cells and thus, its, level would keep on increasing., , (v) The other hormone secreted by the structure which, secrete insulin also, is, (a) somatostatin, (b) cortisol, (c) prolactin, (d) aldosterone, (a) Pancreas secretes insulin, glucagon and somatostatin., The secretion of insulin and glucagon is inhibited by, somatostatin., , endocrine system (chemical and hormonal coordination), is necessary., , 3. Distinguish between endocrine and exocrine, , glands., (ii) Endocrine gland, (NCERT), , (i) Exocrine gland is a gland that pours its secretion on, the surface or into a particular region by means of, ducts for performing a metabolic activity, e.g., sebaceous glands, sweat glands, salivary glands, etc., (ii) Endocrine gland is a gland that pours its secretion, into blood or lymph for reaching the target organ, because the gland is not connected with the target, organ by any duct. It is also known as ductless gland., (iii) Hormones are non-nutrient chemicals which act as, intercellular messengers and are produced in trace, amount., , 2. Why is chemical and hormonal coordination, , necessary?, The nerve fibres do not innervate all the cells of the body, and cellular functions need to be regulated in a, continuous manner. So, to regulate this coordination,, , Differences between endocrine and exocrine glands are, as follows, Endocrine Glands, , Exocrine Glands, , They do not have ducts., , They have ducts., , They secrete hormones, directly into the blood., , They secrete their secretions, into the ducts., , e.g. thyroid, hypothalamus, e.g. sweat and oil glands (of, pituitary, etc., skin) liver and salivary glands., , 4. Comment ‘hormones are called informational, , molecules’., Hormones are known as informational molecules because, their synthesis takes place in one part of the body, i.e. the, endocrine cells and are carried by the blood to another, part of the body, i.e. target organ or tissues where they, stimulate or inhibit the specific physiological processes, according to the need of the body.

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170, , CBSE Term II Biology XI, , 5. Diagrammatically indicate the location of the, , various endocrine glands in our body., , (NCERT), , Location of different endocrine glands, Hypothalamus, , Pineal gland, , Pituitary gland, Thyroid and parathyroid, glands, Thymus gland, Pancreas, Adrenal gland, , Ovaries, (in female), Testes (in male), , 6. How are the hypothalamic hormones transported to, , target organs?, The hypothalamic hormones secreted by the, neurosecretory cells called nuclei are transported through, the hypothalamic axons and released from their nerve, endings and mixed with blood of hypophyseal portal vein., These are then transported to anterior pituitary., The posterior pituitary hormones pass through the axons, that reach the posterior pituitary and remain stored in the, axon terminals, till they are stimulated for release., , 7. Draw a neat and labelled diagram of the pituitary, , gland with hypothalamus connection also showing, its various hormones., Hypothalamus, Influndibulum, Adenohypophysis, GH (general body growth), TSH (thyroid stimulation), ACTH (adrenal cortex stimulation), FSH (gonad stimulation,, LH or, follicle development), ICSH (gonad stimulation, interstitial cell, MSH, development), Oxytocin (pigmentation) Prolactin, (breast, (milk ejection,, development, labour pain initiation), milk formation), , Neurohypophysis, ADH, (water, reabsorption, from DCT), , Pituitary hormones and their major hormones, , 8. Why the pituitary gland is called ‘master gland of, , endocrine orchestra’?, Pituitary gland secretes several hormones, e.g. TSH,, ACTH, etc., which in turn regulate the functioning of, other endocrine gland. That is why it is called master, gland of endocrine orchestra. But pituitary gland itself is, being controlled by the hormones released by the, hypothalamus of the brain., , 9. Briefly mention the mechanism of action of FSH., (NCERT), , In males, FSH and androgens regulate spermatogenesis., In females, FSH stimulates growth and development of, the ovarian follicles. It stimulates the secretion of, oestrogen in ovaries., , 10. A milkman is very upset one morning as his cow, , refuses to give any milk. The milkman’s wife gets, the calf from the shed. On fondling by the calf, the, cow gave sufficient milk., Describe the role of endocrine gland and pathway, associated with this response., (NCERT Exemplar), The fondling by the calf stimulates the release of oxytocin, from the posterior pituitary. Oxytocin brings about, contraction of the smooth muscles of the mammary glands, that causes ejection of milk., , 11. Which hormones are secreted by the posterior, , pituitary gland? What function does each serve?, Where are these hormones actually produced? How, are these hormones transported to the region from, where they are released?, Oxytocin and vasopressin are secreted by the posterior, pituitary gland., (i) Oxytocin is released into the blood when, hypothalamic neurons are stimulated by the, widening of uterus at the time of delivery or by the, sucking of breasts by an infant. It induces, contraction of smooth muscles of the uterus during, the birth of a youngone and myoepithelial cells of, mammary glands to cause release of milk during, sucking by an infant. Therefore, it is also known as, ‘birth hormone’., (ii) Vasopressin is also called Antidiuretic Hormone, (ADH). It decreases the loss of water in urine by, increasing reabsorption of water in distal convoluted, tubules, collecting tubules and collecting ducts of, kidneys., , 12. Which hormone is responsible for maintenance of, , diurnal rhythm of our body? Mention its source., The hormone responsible for diurnal rhythm of our body, is melatonin. The source of its secretion is pineal gland., , 13. George comes on a vacation to India from US. The, , long journey disturbs his biological clock and he, suffers from jet lag. What is the cause of his, discomfort?, Jet lag is caused by the disruption of the body clock as it, is out of synchronisation with the unfamiliar time zone of, the two different parts of the world. The body, experiences different patterns of light and dark then it is, normally used to which disrupts the natural sleep-wake, cycle., Melatonin is a hormone that plays a key role in body, rhythms and jet lag. After the sun sets, the eyes perceive

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171, , CBSE Term II Biology XI, , darkness and alert the hypothalamus to begin releasing, melatonin, which promotes sleep. Conversely, when the, eyes perceive sunlight, they tell the hypothalamus to, with-hold melatonin production. However, the, hypothalamus cannot read just its schedule instantly, it, takes several days., , 14. Which endocrine gland is called the ‘biological, , clock’ and why?, Pineal gland may be called as the ‘biological clock.’ Its, secretion is melatonin which has antigonadotrophic, effect. The gland receives photoperiod information via, neural circuit from the eyes. Pineal gland also controls, annual rhythm of reproduction. The seasonal changes in, photoperiod may be translated into physiological effect, via the pineal and its endocrine products., , 15. Give the name of the endocrine gland that produces, , calcitonin and also mention the role played by this, hormone., Calcitonin (CT) or thyrocalcitonin hormone is produced, by thyroid glands., It is hypocalcemic and hypophosphatemic peptide, hormones, which check excess plasma Ca 2 + and phosphate, by decrease mobilisation from bones., , 16. Write short notes on the functions of the following, , hormones, (i) Parathyroid hormone (PTH), (ii) Thyroid Hormones, (iii) Thymosins, , (NCERT), , (i) Functions of PTH are as follows, l, , l, , It increases the level of Ca 2+ in the blood., It stimulates the process of bone reabsorption, (i.e. dissolution/demineralisation) by acting on bones., , (ii) Functions of thyroid hormones are as follows, l, , l, , These hormones regulate and maintain the Basal, Metabolic Rate (BMR), i.e. both T3 and T4 hormones, increase, the overall metabolic rate of the body., These support the process of formation of red blood, cells and also help in controlling the metaboilsm of, carbohydrates, proteins and fats., , (iii) Functions of thymosins are as follows, Thymosins, when released in the blood has a, stimulating effect on the entire immune system., Apart from this, thymosin also promotes the, production of antibodies to the provide humoral, immunity., , 17. In countries where dietary intake of iodine is low,, , goitres, enlargement of the thyroid are common., What would you say about the chain of events, leading to the formation of goitre?, In the absence of iodine, neither thyroxine nor, triiodothyronine hormone is produced, due to which, their concentration in the blood decreases. To, compensate this, the anterior pituitary secretes large, amounts of TSH, which stimulates the growth of the, , thyroid gland, sometimes to gigantic proportions, thus, leading to the formation of goitre., However, enlargement of the gland cannot increase, production of the hormones, because of the deficiency of, the of main ingredient, i.e. thyroxine hormone., , 18. Differentiate between insulin and glucagon., Differences between insulin and glucagon are as follows, Insulin, , Glucagon, , It is a hormone secreted by, beta cells of pancreas., , It is a hormone secreted by, alpha cells of the pancreas., , It is secreted in response to, high blood sugar level., , It is secreted in response to, low blood glucose level., , It makes muscle, red blood, cells and fat cells to take up, glucose in from the blood., , If functions to cause the liver, to release stored glucose, from its cells into the blood., , 19. Mention the difference between hypothyroidism, , and hyperthyroidism., , (NCERT Exemplar), , Hypothyroidism is low secretion of thyroxine hormone., Hyperthyroidism is oversecretion of thyroid hormone. It, occurs due to low or hyperactivity of the thyroid gland., , 20. What are the effects of hypothyroidism (observed, , during pregnancy) on the development and, maturation of a growing baby?, (NCERT Exemplar), Hypothyroidism during pregnancy causes defective, development and maturation of the growing baby leading, to stunted growth (cretinism), mental retardation, low, intelligence, abnormal skin, deaf-mutism, etc., , 21. On an educational trip to Uttarakhand, Ketki and, , her friends observed that many local people were, having swollen necks. Please help Ketki and her, friends to find out the solutions to the following, questions., (i) Which probable disease are these people suffering, from?, (ii) How is it caused?, (iii) What effect does this condition have on, pregnancy?, (NCERT Exemplar), (i) The people are suffering from the goitre disease., (ii) Goitre is caused by deficiency of iodine which leads, to the hypothyroidism., (iii) It leads to defective development of foetus and birth, of child with cretinism., , 22. Calcium plays a very important role in the, , formation of bones. Write about the role of, endocrine glands and hormones responsible for, maintaining calcium homeostasis. (NCERT Exemplar), The secretion of Parathyroid Hormone (PTH) regulates, the concentration of calcium ions ( Ca 2+ )., Parathyroid hormone increases the Ca 2+ levels in the, blood, It acts on bones and stimulates the process of bone, resorption (dissolution/ demineralisation). It also

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172, , CBSE Term II Biology XI, , stimulates reabsorption of Ca 2+ by the renal tubules and, increases Ca 2+ absorption from the digested food. It is, thus, clear that PTH is a hypercalcemic hormone, i.e. it, increases the blood Ca 2+ levels. Along with TCT, it plays, a significant role in calcium balance in the body., , 23. When does the secretion of adrenocorticotropin, , take place in the body? What is the purpose of its, secretion?, Adrenocorticotropin is secreted when, Adrenocorticotropin Releasing Hormone (ACRH), stimulates the corticotroph cells of the anterior lobe of, pituitary gland., It is released because its stimulation is responsible for the, synthesis and secretion of glucocorticoid steroid hormone, from the adrenal cortex of adrenal gland., , 24. How do you justify the statement that hormones of, , adrenal medulla are emergency hormones?, Hormones of adrenal medulla, i.e. adrenaline and, nor-adrenaline (belong to the category of compounds, called catecholamines) are secreted in response to any, kind of stress, danger and during emergency situations, like fall in blood pressure or sugar, increase respiratory, rate and heartbeat. CNS at the time of stress or danger, stimulates adrenal medulla to release these hormones. All, these conditions need more energy for their action. As, these hormones prepare the body to face stress or danger, hence, these are called emergency hormones., , 25. Inflammatory responses can be controlled by a, , certain steroid. Name the steroid, its source and, also its other important functions. (NCERT Exemplar), Inflammatory responses are controlled by steroid, hormones called glucocorticoids, which are secreted by, adrenal cortex. Its other functions are to stimulate, gluconeogenesis, lipolysis and proteolysis and inhibit, cellular uptake and utilisation of amino acids., , 28. Give examples of, (i) hyperglycemic hormone and hypoglycemic, hormone, (ii) hypercalcemic hormone, (iii) gonadotropic hormone, (iv) progestational hormone, (v) blood pressure lowering hormone, (vi) androgens and oestrogens, (NCERT), (i) Glucagon and insulin, respectively, (ii) Parathyroid hormone, (iii) Follicle Stimulating Hormone (FSH) and Luteinizing, Hormone (LH), (iv) Progesterone, (v) Atrial Natriuretic Factor (ANF), (vi) Androgens are mainly testosterone and oestrogens, include oestriol, oestradiol and oestrone., , 29. Correct the following statements by replacing the, , term underlined., (i) Insulin is a steroid hormone., (ii) TSH is secreted from the corpus luteum., (iii) Tetraiodothyronine is an emergency hormone., (iv) The pineal gland is located on the anterior part of, the kidney., (NCERT Exemplar), (i), (ii), (iii), (iv), , Insulin is a proteinaceous hormone., TSH is secreted from the thyroid glands., Adrenaline is an emergency hormone., The pineal gland is located on the dorsal side of the, forebrain., , 30. Fill up the blank spaces (i)-(vi) in the table given, , below., Names of, Secreted, Endocrine Gland Hormones, , Functions of the, Hormone, , Differences between hyperglycemia and hypoglycemia, are as follows, , Pituitary, , (i) .........., , Reabsorption of water and, electrolytes in kidney., , Hyperglycemia, , Hypoglycemia, , (ii) .........., , Insulin, , (iii)....., , It results from hyposecretion, of insulin., , It results from, hypersecretion of insulin., , Thymus, , Thymosins, , (iv)....., , Its symptoms include high, blood glucose level,, breakdown of muscles, tissues,, loss of weight and tiredness., , Its symptoms include low, blood glucose level, hunger,, sweating, irritability, double, vision., , Ovary, , (v) ..... and, (vi) ....., , 26. Differentiate between hyperglycemia and, , hypoglycemia., , 27. State whether True or False., (i) Pars distalis produces six trophic hormones., (ii) B-lymphocytes provide cell-mediated immunity., (iii) Insulin resistance results in a disease called, (NCERT Exemplar), diabetes mellitus., (i) True, , (ii) False, , (iii) True, , (i), (ii), (iii), (iv), (v), (vi), , Development of growing, ovarian follicles controls, metabolism of proteins,, fats and carbohydrates., , Vasopressin, Pancreas, Reduces blood glucose level, Differentiation of T-lymphocytes, Oestrogen, Progesterone

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173, , CBSE Term II Biology XI, , 31. Mention the major classes of hormones being in, , 34. Explain amplification of a signal in hormone action., , humans. Give examples of each., , What is its role?, , Although hormones are chemically diverse, they, generally belong to one of four different chemical, groups, (i) Steroid Hormones These hormones are, manufactured by endocrine cells from cholesterol,, an important type of lipid in the human body., Examples include cortisol, aldosterone, oestrogen,, progesterone and testosterone., (ii) Amino Acid Derivatives The thyroid hormones, (T3 and T4 ) are synthesised from the amino acid, tyrosine and iodide, respectively. Adrenaline (also, known as epinephrine) and nor-adrenaline (also, known as nor-epinephrine) are produced by the, medulla of the adrenal gland and these are also, derived from tyrosine., Melatonin is synthesised from the amino acid, tryptophan., (iii) Protein Hormones These hormones are long,, folded chains of amino acids. Included among, these hormones are insulin, glucagons, parathyroid, hormone, growth hormone, prolactin, etc., (iv) Peptide Hormones Hormones such as oxytocin, and antidiuretic hormone are smaller than protein, hormone. They are made up of a short chain of, amino acids., , Although hormones are present in very small amounts,, they effectively regulate many physiological processes., This is the result of signal amplification, an increase in, signal strength. For example, a single hormone receptor, complex can stimulate the production of many cAMP, molecules. In turn, each cAMP can activate a protein, kinase that phosphorylates many protein molecules. In this, way, a single hormone molecule can activate many, proteins., , 32. (i) What is termed as first messenger and second, messenger in the target cells., (ii) How do protein hormones act on target cells?, (i) Hormone is called first messenger and cAMP is, called second messenger., (ii) Protein hormone is water soluble, it binds to the, extrinsic receptor present on the cell surface of the, plasma membrane. Hormones when bind to them, activate a membrane bound enzyme adenyl cyclase,, which catalyses the conversion of ATP to cAMP., The cAMP then activates one more enzymes, known as protein kinases. After phosphorylation of, protien, alteration of its function occurs which, thereby, leads to some metabolic effect., , 33. What is the role of second messenger in protein, , hormone action?, , (NCERT Exemplar), , Hormones which do not enter the target cells, interact, with specific receptors located on the surface of the, target cell membranes and generates second messengers, (e.g. cAMP) on the inner side of the plasma membrane., The second messenger, in turn, carries out all the, hormonal functions., , 35. What is meant by ‘antagonistic effect’? Illustrate your, , answer with an example., It refers to the effect of a hormones that are countered by, an antagonistic (opposing) signal, often another hormone., For example, the sympathetic and parasympathetic nervous, systems achieve antagonistic effect on heartbeat., This mechanism involves the use of more than one second, messenger. In heart cells cyclic form of Adenosine, Monophosphate (cAMP), serves as a second messenger,, speeding up muscle cell contraction in response to, adrenaline, while cyclic Guanosine Monophosphate, (cGMP) serves as another second messenger, slowing, muscle contraction in response to acetylcholine., , 36. Write short note on feedback mechanism of hormone, , action., The regulation of hormonal secretion in the body of an, organism is called feedback control. This helps to maintain, a homeostasis within the endocrine system., Feedback control is of two types, (i) Negative feedback where the end product of a, biochemical process inhibits its own production, e.g., regulation of release of thyroxine hormone., (ii) Positive feedback, where hormones released by one, gland stimulates other gland which further lead to, even more significant changes in the same direction., , 37. Write a note on hormone receptors., Hormones are released from their respective gland in very, small amount. They carry out widespread effects in the, body of an individual. Their response is very specific and, accurate. Their effects are produced on target tissues by, binding to the specific proteins known as hormone, receptors, located in the target tissues only., Hormone receptors are of following two types, (i) Membrane Bound Receptors Hormone receptors, present on the cell membrane of the target cells., (ii) Intracellular Receptors Hormone receptors present, inside the target cell, e.g. nuclear receptor (present in, the nucleus of a cell).

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174, l, , CBSE Term II Biology XI, , Long Answer (LA) Type Questions, 1. Hypothalamus is a super master endocrine gland., , Elaborate., , (NCERT Exemplar), , Hypothalamus regulates a wide spectrum of body, functions. It contains several groups of neurosecretory, cells called nuclei, which produce hormones. These, hormones regulate the synthesis and secretion of pituitary, hormones. However, the hormones produced by, hypothalamus are of two types, the releasing hormones, (which stimulate secretion of pituitary hormones) and the, inhibiting hormones (which inhibit secretions of pituitary, hormones)., The hormones reach the pituitary gland through a portal, circulatory system and regulate the functions of the, anterior pituitary. The posterior pituitary is under the, direct regulation of hypothalamus., The oxytocin and vasopressin are the two hormones, synthesised by hypothalamus that are transported to, posterior pituitary., , 2. Explain the following by giving scientific reasons., (i) Hypothalamus and pituitary function as an, integrated and coordinated system., (ii) Body growth is greatly accelerated at puberty in, males., (i) The hypothalamus and pituitary function as an, integrated and coordinated system because both of, them are connected at the base of the brain., They interact to each other in two ways, (a) By the hypophyseal portal system, which is a, system of blood vessels that connect part of, hypothalamus to the anterior lobe of pituitary, gland. Hypothalamus secretes hormones into, this portal system and the hormones act on the, anterior pituitary, triggering the synthesis/, secretion of pituitary hormone., (b) The other is that they have direct anatomical, connection between the hypothalamus and the, posterior lobe of pituitary (posterior pituitary is, actually are extension of hypothalamus)., (ii) Puberty is the phenomenon of physical changes by, which child’s body matures into an adult male,, capable of sexual reproduction to enable fertilisation., It is initiated by the hormonal signals from the brain, to the gonads, i.e. testes in a male. In response to the, signals, gonads produce hormones that in turn, stimulates the growth, function and transformation of, the brain, muscles, blood, hair, sexual organs, etc. An, androgen called as testosterone in males, functions as, principal sex hormone, producing all changes in male, related to growth and development at puberty., , 3. List the hormones secreted by the following., (i) Hypothalamus, (ii) Pituitary, (iii) Thyroid, (iv) Parathyroid, (NCERT), (v) Adrenal, (vi) Pancreas, , Hormones secreted by the following glands are, (i) Hypothalamus secretes thyrotropin releasing, hormone, adrenocorticotropin releasing hormone,, gonadotropin releasing hormone, somatotropin, releasing hormone, prolactin releasing hormone,, melanocyte stimulating hormone, releasing, hormone., (ii) (a) Pars distalis part of pituitary (anterior pituitary), secretes Growth Hormone (GH), Prolactin, (PRL), Thyroid Stimulating Hormone (TSH),, Adrenocorticotropic Hormone (ACTH),, Luteinizing Hormone (LH), Follicle Stimulating, Hormone (FSH)., (b) Pars intermedia secretes Melanocyte Stimulating, Hormone (MSH)., (c) Pars nervosa secretes oxytocin and vasopressin., (iii) Thyroid secretes thyroxine (T4 ) and triiodothyronine, (T3 )., (iv) Parathyroid secretes Parathyroid Hormone (PTH)., (v) Adrenal, (a) secretes adrenaline, nor-adrenaline from adrenal, medulla., (b) also secretes corticoids (glucocorticoid and, mineralocorticoid) and sexocorticoids from, adrenal cortex., (vi) α-cells of pancreas secrete glucagon, while the, β-cells secrete insulin. The delta cells (δ) secrete, somatostatins., , 4. What are the hormones of adenohypophysis and, , also write their target organs?, , (NCERT Exemplar), , The anterior lobe of pituitary is called adenohypophysis., It secretes various hormones. These are as follows, (i) Somatotropic Hormone (STH) or Growth Hormone, (GH) target the cells which undergo growth., (ii) Thyroid Stimulating Hormone (TSH) or Thyrotropin, influence the cells of thyroid gland., (iii) Prolactin Hormone (PRL) or Mammotrophin, Hormone (MTH) or Luteotrophin Hormone (LTH), called the ‘hormone of maternity’ activates mammary, glands during pregnancy and after childbirth., (iv) Adrenocorticotropic Hormone (ACTH) stimulates, cortex of adrenal gland., (v) Gonadotropic hormones are of two types, (a) Follicle Stimulating Hormone (FSH) stimulates, the growth of ovarian follicles., (b) Luteinizing Hormone (LH) acts on corpus, luteum to secrete progesterone but in males it, activates cells of Leydig to secrete androgens., , 5. (i) Give a diagrammatic representation of the, mechanism of protein hormone (e.g. FSH) action., (ii) Illustrate the differences between the mechanism, of action of a protein and a steroid hormone., (NCERT Exemplar)

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175, , CBSE Term II Biology XI, , (i) Diagrammatic representation of the mechanism of, hormone action of peptide or protein hormone, Hormone (e.g. FSH), Receptor, , Formation of hormone, receptor complex, , Ovarian cell, membrane, , Response I, , ⇒, Generation of second messenger, 2, (cyclic AMP or Ca +), , ⇒, Biochemical response, , ⇒, Physiological response, (ovarian growth), , (ii) Differences between mechanism of action of, a protein and a steroid hormone are as follows, Protein Hormones, , Steroid Hormones, , They interact with, membrane bound, receptors., , They interact with, intracellular receptors., , They generate second, They regulate gene, messengers, expression or chromosome, (cyclic AMP, IP 3, Ca 2+ , function by the interaction of, hormone receptor complex, etc)., with the genome., The second messengers Cumulative biochemical, action of hormone receptor, regulate cellular, complex results in, metabolism., physiological and, developmental effects., l, , Case Based Questions, 1. Refer to the diagram given below and answer the, , following questions., Parathyroid glands, , Parathyroid hormone increases the level of Ca 2+ in the, blood. It stimulates the process of bone reabsorption (i.e., dissolution/demineralisation) by the action on bones., It also stimulates reabsorption of Ca 2+ by the renal tubules, and absorption of Ca 2+ from the digested food. By the, above mentioned functions of parathyiond hormone, it is, clear that PTH acts as a hypercalcemic hormone (increases, the level of Ca 2+ in the blood)., , (iii) Mention the structural characteristic of parathyroid, gland., Parathyroid glands are four in number, i.e. each pair is, situated in the two lobes of the thyroid gland on either side., These are small, flat and oval gland., , (iv) What does the hormone of parathyroid gland called?, Which ion regulate the level of these hormones?, Parathyroid glands secrete a single hormone known as, parathormone or Parathyroid Hormone, i.e. PTH, (functions opposite to the thyrocalcitonin hormone). The, secretion of PTH is regulated by the circulating level of, calcium ions in the blood., , 2. Direction Read the following passage and answer the, , questions that follows., Lakshita was studying endocrine system for her unit, test. She was confused how hormones produce their, effects on the target tissue. She read many times, but, still did not understand the process. She asked the, same to her neighbour Stuti, a biology teacher in a, school. Stuti explained her about the hormone, receptor complex through diagrams and flowcharts., (i) Name the two types of receptors., Two types of receptors are, (a) membrane bound extracellular receptors,, (b) intracellular receptors., , (ii) Why do different hormones use different types of, receptors?, The hormones which cannot enter the target cell, need, membrane bound (extracellular) receptors and the, hormones which can enter the target cell, need, intracellular (mostly nuclear) receptors., , (iii) What are second messengers? Give two examples?, Second messengers are those chemicals, which are, generated in the target cells, by those hormones which, cannot enter the cells, to bring about the biochemical, changes, e.g. Inositol Triphosphate (IP 3 ) cyclic Adenosine, Monophosphate (cAMP)., , (i) What is the relation of parathyroid gland and, thyroid gland?, Parathyroid glands are small glands in the human neck, that produces parathyroid hormone. These glands are, situated on the posterior side of the thyroid gland., , (ii) Why is parathyroid hormone called a, hypercalcemic hormone?, , (iv) Mention the role of second messenger in the, mechanism of protein hormone action., Second messenger regulate the metabolism of a cell, which, results in many physiological effects., , (v) Give the name of the major classes of hormones., The major classes of hormones are, (a) Steroid hormones, (b) Amino acid derivatives,, (c) Protein hormones, (d) Peptide hormones

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Chapter Test, Multiple Choice Questions, , 1. The posterior pituitary gland is not a ‘true’ endocrine, gland because, (a) it is provided with a duct, (b) it only stores and releases hormones, (c) it is under the regulation of hypothalamus, (d) it secretes enzymes, , 2. Identify the hormone with its correct matching of, , these questions also has four alternative choices, any, one of which is the correct answer. You have to select one, of the codes (a), (b), (c) and (d) given below., (a) Both A and R are true and R is the correct explanation of A, (b) Both A and R are true, but R is not the correct explanation, of A, (c) A is true, but R is false, (d) A is false, but R is true, , 1. Assertion (A) Endocrine glands are called ductless, , source and function., , glands., , (a) Oxytocin – Posterior pituitary, growth and maintenance of, mammary glands, (b) Melatonin – Pineal gland, regulates the normal rhythm of, sleep-wake cycle, (c) Progesterone – Corpus luteum, stimulation of growth and, activities of female secondary sex organs, (d) Atrial natriuretic factor – Ventricular wall increases the, blood pressure, , Reason (R) Hormones produced by endocrine glands, are released into the blood and transported to distant, target organs., , 3. Which of the following is true for ‘parathormone’?, (a) It increases blood calcium level and decreases calcium, store of the bone, (b) It decreases blood calcium level and increases calcium, store of the bone, (c) It increases blood glucose level and decreases calcium, store of the bone, (d) It decreases blood glucose level and increases calcium, store of the bone, , 4. The layer of adrenal cortex from outer to inner region, , 2. Assertion (A) Pineal gland secretes two biogenic, hormones., Reason (R) Serotonin is secreted by pituitary gland., , 3. Assertion (A) Pancreas is a composite gland., Reason (R) It acts both as an exocrine and an, endocrine gland., , Short Answer Type Questions, , 1. Name the T3 and T4 components of thyroid hormones., Explain their specification., , 2. Which hormonal deficiency is responsible for the, following?, (i) Diabetes mellitus (ii) Goitre, , are, (a), (b), (c), (d), , zona glomerulosa, zona fasciculata, zona reticularis, zona reticularis, zona glomerulosa, zona fasciculata, zona fasciculata, zona reticularis, zona glomerulosa, zona reticularis, zona fasciculata, zona glomerulosa, , 5. Hormones that interact with membrane bound, receptors normally, , 3. Enlist the functions of glucagon in human body., 4. How does progesterone function in a human female?, 5. What is meant by synergistic effect? Explain with an, example., , Long Answer Type Questions, , (a) enters into the cell membrane, (b) do not enter into the cell, (c) generate secondary messenger, (d) Both (b) and (c), , 1. ‘Adrenal cortex releases variety of hormones which, have different regulatory effects in human body’. Justify, this statement by explaining different hormones, secreted by adrenal cortex and their functions., , Assertion-Reasoning MCQs, Direction (Q. Nos. 1-3) Each of these questions contains, two statements, Assertion (A) and Reason (R). Each of, , 2. Explain the structure of pancreas and also mention the, role of the hormone secreted by it., , Answers, Multiple Choice Questions, 1. (b), , 2. (b), , 3. (a), , 4. (a), , Assertion-Reasoning MCQs, 1. (a), , 2. (c), , 3. (a), , (iii) Cretinism, (NCERT), , 5. (d), , For Detailed Solutions, Scan the code

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Biology, Class 11th ( Term II ), , Practice Paper 1, , *, , (Solved), Time : 2 Hours, Max. Marks : 35, , General Instructions, , 1. There are 9 questions in the question paper. All questions are compulsory., 2. Question no. 1 is a Case Based Question, which has five MCQs. Each question carries one mark., 3. Question no. 2-6 are Short Answer Type Questions. Each question carries 3 marks., 4. Question no. 7-9 are Long Answer Type Questions. Each question carries 5 marks., 5. There is no overall choice. However, internal choices have been provided in some questions. Students have to attempt, only one of the alternatives in such questions., , * As exact Blue-print and Pattern for CBSE Term II exams is not released yet. So the pattern of this, paper is designed by the author on the basis of trend of past CBSE Papers. Students are advised, not to consider the pattern of this paper as official, it is just for practice purpose., , 1. Direction Read the following passage and answer the questions that follows., In a lecture on cell cycle and its division, the teacher taught the two basic stages of cell cycle viz, interphase, and M-phase. She also taught about the substages of each basic stage and their significance. After that she, asked some questions which are as follows., (i) What is the average duration of cell cycle in humans and yeast?, (a) 20 hrs, 60 min, (c) 30 hrs, 120 min, , (b) 24 hrs, 90 min, (d) 22 hrs, 70 min, , (ii) The interphase is divided into three main phases. Three phases are, (a) G1 -phase, M-phase and G2 -phase, (c) G1 -phase, synthesis phase and G2 -phase, , (b) M-phase, S-phase and divisional phase, (d) M-phase, G2 -phase and divisional phase, , (iii) Choose the correct sequence of two main events in mitosis., (a) Karyokinesis followed by cytokinesis, (b) Cytokinesis followed by karyokinesis, (c) Karyokinesis followed by separation of the daughter cells, (d) Cytokinesis followed by separation of the daughter cells, , (iv) Which of the following events takes place during diplotene stage of prophase-I of meiosis?, (a) Compaction of chromosomes, (c) Formation of synaptonemal complexes, , (b) Formation of recombination nodules, (d) Dissolution of synaptonemal complex, , (v) Splitting of centromere and hence separation of chromatids occurs during, (a) prophase-II, (c) anaphase-II, , (b) anaphase-I, (d) metaphase-II

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178, , CBSE Term II Biology XI, , 2. Even though a very few cells in a C 4 -plant carry out, the biosynthetic Calvin pathway, yet they are highly, productive. Can you discuss why?, Or Does pyruvic acid enter the Krebs’ cycle directly?, , 3. What are the assumptions made during the, calculation of net gain of ATP?, , 4. Write the role of diaphragm and intercostal muscles, in the inspiration process., , 5. Explain how during light reaction of photosynthesis,, ATP synthesis as a chemiosmotic phenomenon takes, place?, Or The role of ethylene is both positive and negative., Justify the statement., , 6. Suggest some ways in which inhibitors are important, , Rate of photosynthesis, , to plant survival in natural adverse conditions., Or The following figure shows the effect of light on, the rate of photosynthesis. Based on the graph,, answer the questions that follows., , E, , B, , C, , (i) At which point(s) (A, B or C) in the curve, light, acts as a limiting factor?, (ii) What could be the limiting factor(s) in region A?, (iii) What do C and D represent on the curve?, , 7. Discuss about the regulation of respiration., Or The glomerular filtrate in the loop of Henle, gets concentrated in the descending and then gets, diluted in the ascending limbs. Explain., , 8. Explain the following by giving scientific reasons, (i) Hypothalamus and pituitary function as an, integrated and coordinated system., (ii) Body growth is greatly accelerated at puberty in, males., Or Give scientific reasons of the following, statements., (i) Adrenals are called glands of emergency., (ii) Parathormone is also called Collip's hormone., (iii) The hormones released by the posterior lobe of, pituitary are not its own products., (iv) Endocrine glands directly release their products, into the blood., , 9. Describe the internal structure of human heart., , A, , Or Which organ is acts as the command and, control system of all body activities in humans?, Discuss about their location and protective, covering., , D, Light intensity, , Explanations, 1. (i) (b) The average duration of cell cycle in humans and yeast, are 24 hrs and 90 min, respectively., (ii) (c) Interphase is divided into three main phases, i.e., G1-phase, Synthesis phase and G 2-phase., (iii) (a) The mitosis phase or M-phase starts with the nuclear, division, corresponding to the separation of daughter, chromosome (karyokinesis) and ends with division of, cytoplasm (cytokinesis). Hence, option (a) is correct., (iv) (d) Prophase-I of meiosis is long and complex. It is further, subdivided into five phases, i.e. leptotene, zygotene,, pachytene, diplotene and diakinesis. During diplotene, stage dissolution of synaptonemal complex takes place., While the other three events take place in leptotene,, pachytene and zygotene phases., (v) (c) Splitting of centromere and hence separation of, chromatids occurs during anaphase-II of meiosis-II., 2. C 4-plants chemically fix carbon dioxide in the cells of the, mesophyll by adding it to the 3 molecule Phosphoenol, Pyruvate (PEP), a reaction catalysed by an enzyme called PEP, carboxylase. It creates the 4 carbon organic acid, oxaloacetic, acid. Oxaloacetic acid synthesised by this process is then, , translocated to specialised bundle sheath cells where the, enzyme, RuBisCO and other Calvin cycle enzymes are located, and where CO2 released by decarboxylation of the 4 carbon, acids is then fixed by RuBisCO enzyme to form, 3-phosphoglyceric acids (3C)., The physical separation of RuBisCO from the oxygen driven, light reactions inhibits photorespiration and increases, CO2-fixation. This way photosynthetic capacity of the, C 4-plants increases many folds than C 3-plants., Or, No, pyruvic acid as such does not enter Krebs’ cycle, pyruvate, is first decarboxylated, and then oxidised by the enzyme, pyruvate dehydrogenase to form acetyl Co-A. This molecule, enters the mitochondria for further oxidation reaction. This is, the connecting link between glycolysis and Krebs’ cycle., During the process, NAD + is reduced to NADH + H + ., The summary of the reaction is given below, Pyruvic acid + Co-A + NAD +, , Pyruvate dehydrogenase, , →, Mg 2+, , Acetyl Co-A + CO2 + NADH + H +

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CBSE Term II Biology XI, , During this process, two molecules of NADH are produced, (from the metabolism of two molecules of pyruvic acid, produced during glycolysis) and thus, it results in a net gain, of 6 ATP molecules (2 NADH × 3 = 6 ATP)., 3. The calculations of net gain of ATP can be made only on, certain assumptions, (i) There is a sequential, orderly pathway functioning with, one substrate forming the next and with glycolysis, TCA, cycle and ETS pathway following one after another., (ii) The NADH synthesised in glycolysis is transferred into, the mitochondria and undergoes oxidative, phosphorylation., (iii) None of the intermediates in the pathway are utilised to, synthesise any other compound., (iv) Only glucose is being respired, no other alternative, substrates are entering in the pathway at any of the, intermediary stages., But this kind of assumptions are not really valid in a living, system. All pathways work simultaneously and do not take, place one after another. Substrates enter the pathways and, are withdrawn from it as and when needed; enzymatic rates, are controlled by multiple means. In overall steps, there is a, net gain of 36 ATP molecules during aerobic respiration of, one molecule of glucose., 4. The diaphragm and intercostal muscles (external and internal), present between the ribs help in generation of a pressure, gradient between the lungs and the atmosphere., During inspiration diaphragm is lowered by contraction of its, muscle fibres and becomes flat. The external intercostal, muscles contract pulling the ribs and sternum upward and, outward. This increases the volume of thoracic cavity and, thus, decrease the intra-pulmonary pressure. The greater, atmospheric pressure outside the body now causes the air to, flow rapidly into external nares, which sequentially leads to, alveoli. Thus, causing inspiration., 5. Chemiosmosis requires a membrane, a proton pump, a proton, gradient and ATP synthase enzyme. Energy is used to pump, protons across a membrane, to create a gradient or a high, concentration of protons within the thylakoid lumen. ATP, synthase enzyme catalyses the formation of ATP, along with, the NADPH produced by the movement of electrons. The, energy carried by ATP molecules will be used immediately in, the biosynthetic reaction taking place in the stroma for fixing, CO 2 and synthesis of sugars., Or The role of ethylene is both positive and negative. Ethylene is, a simple gaseous PGR. It is synthesised in large amount by, tissues undergoing senescence and ripening. It also promotes, senescence and abscission of plant organs especially of leaves, and flowers. This is its negative effect., As it’s positive effect, ethylene breaks seed and bud, dormancy, initiates germination in peanut seeds, sprouting of, potato tubers. It promotes internode/petiole elongation in, deep water rice plants. It helps leaves/ inner parts of the, shoot to remain above water., 6. Inhibitors are important to the survival of higher plants in, temperate zones where there are extreme variation in, weather conditions prevails. Here plants become dormant, during harsh winter period and become active plant on, coming favourable conditions. Seeds often will not begin to, , 179, germinate until they have been exposed to cold. The breaking, of dormancy and the beginning of growth depend on the, release from inhibition of metabolic activities., Or (i) At points B and C of the curve, the rate of photosynthesis, did not increase with an increase in its intensity, because, light becomes a limiting factor under these conditions., (ii) In A region, the rate of photosynthesis shows, proportionate increase upto a certain CO2 concentration,, beyond which the rate again becomes constant., (iii) Points C and D represent that if the light intensity is, doubled, CO2 concentration again becomes limiting factor, beyond this concentration., 7. The respiratory rhythm can be maintained and moderated by, human beings to suit the demands of the body tissues., It is under dual control, i.e. nervous and chemical. This is, explained below as, 1. Neural Control The respiratory rhythm centre is, composed of a group of neurons located in the medulla, oblongata and pons Varolii. A chemosensitive area is, located adjacent to rhythm centre that is highly sensitive, to CO2 and hydrogen ions., They increase activity of this centre, which in turn signals, the respiratory centre to make necessary changes in order, to eliminate these substances. Oxygen does not have a, significantly direct effect on the respiratory centre of the, brain in controlling respiration., 2. Chemical Control Large number of chemoreceptors are, located in the carotid bodies, which lie bilaterally in the, bifurcations of the common carotid arteries. Their, afferent nerve fibres pass through glossopharyngeal, cranial nerve and thus, to dorsal respiratory area of the, medulla oblongata. Receptors of aortic arch and carotid, artery recognise changes in CO2 and H + concentration, and send necessary signals to the rhythm centre for, remedial actions., Or The gradient of increasing hyperosmolarity of medullary, interstitium is maintained by a counter-current mechanism, and the proximity between the Henle’s loop and vasa recta., This gradient is mainly caused by NaCl and urea. The, transport of these substances facilitated by the special, arrangement of Henle’s loop and vasa recta is called the, counter-current mechanism. NaCl is transported by the, ascending limb of Henle’s loop, which is exchanged with the, descending limb of vasa recta. NaCl is returned to the, medullary interstitium by the ascending part of vasa recta., But, contrarily, the water diffuses into the blood of ascending, limb of vasa recta and is carried away into the general blood, circulation., Permeability to urea is found only in the deeper parts of thin, ascending limbs of Henle’s loops and collecting ducts. Urea, diffuses out of the collecting ducts and enters into the thin, ascending limb. A certain amount of urea recycled in this way, is trapped in medullary interstitium by the collecting tubule., This mechanism helps in the maintenance of a concentration, gradient in the medullary interstitium. Presence of such, gradient helps in an easy passage of water from the collecting, tubule, resulting in the formation of concentrated urine, (filtrate), i.e. nearly four times concentrated than the initial, filtrate formed.

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180, , CBSE Term II Biology XI, , (a) By the hypophyseal portal system, which is a, system of blood vessels that connects part of, hypothalamus to the anterior lobe of pituitary, gland. Hypothalamus secretes hormones into this, portal system and the hormones act on the, anterior pituitary, triggering the synthesis/, secretion of pituitary hormone., (b) The other is that they have direct anatomical, connection between the hypothalamus and the, posterior lobe of pituitary (posterior pituitary is, actually an extension of hypothalamus). Thus, it is, said that hormones released through posterior, pituitary are actually released from the, hypothalamus., (ii) Puberty is the phenomenon of physical changes by which, child’s body matures into an adult male, capable of sexual, reproduction to enable fertilisation. It is initiated by the, hormonal signals from the brain to the gonads, i.e. testes in, a male., In response to the signals, gonads produce hormones that, in turn stimulate libido and the growth, function and, transformation of the brain, muscles, blood, hair, sexual, organs, etc. An androgen called as testosterone in males,, functions as principal sex hormone, producing all changes, in male related to growth and development at puberty., Or (i) It is called so, because hormones of adrenal medulla, increase the metabolism for preparing the animal to face, physical, emotional stress as well as emergencies which, could be life threatening., (ii) It is called so, because a Canadian Endocrinologist James, B Collip discovered parathormone in 1925., (iii) The hormones released by posterior lobe of pituitary, gland are, in fact, synthesised by the neurons in the, hypothalamus and sent to the former via axons for release., (iv) Endocrine glands are ductless glands and their products, act at a distant organ or tissue., 9. Internally, the chambers of heart, i.e. two auricles (atria) and, ventricles are separated by different septa and valves., Auricles (Atria), These are the upper two thin-walled and smaller chambers., They serve to receive the blood, therefore are called, receiving chambers (right atrium and left atrium). Both the, right and the left atria are separated by a thin, muscular wall,, known as interatrial septum., (i) Right Atrium This right chamber deals with only impure, (deoxygenated) blood. It receives impure blood from, various parts of the body, through two major veins, i.e., superior and inferior vena cava., It also receives blood from the walls of the heart itself, (through a coronary sinus)., (ii) Left Atrium This chamber is meant to deal with only, pure (oxygenated) blood. It receives blood (pure) from, , lungs through two pulmonary veins (i.e. one from the each, lung)., Ventricles These are lower two chambers of the heart, that, pumps the blood away from the heart. These functions as, pumping chambers. Both the right and the left ventricles, are separated by the interventricular septum., The atrium and the ventricle of the same side are also, separated by another septum, a thick fibrous tissue called, Atrio-Ventricular septum (i.e. AV septum)., Arch of, aorta, , Right pulmonary, artery, Right pulmonary, veins, , Pulm, arter onary, y, , 8. (i) The hypothalamus and pituitary function as an integrated, and coordinated system because both of them are, connected at the base of the brain., They interact to each other in the following two ways, , Left pulmonary artery, Left pulmonary veins, Left atrium, , Right atrium, , Right ventricle, , Left ventricle, Chordae tendineae, Interventricular, septum, , (i) Right Ventricle It receives impure blood from right, atrium and pumps blood into pulmonary artery, which, further takes this blood to lungs for purification., (ii) Left Ventricle It receives pure (oxygenated) blood from, left atrium and pumps its pure blood to aorta (largest, artery in the pathway), which in turn takes this blood to, whole body and organs., Or The brain is the central information processing organ of our, body and acts as the ‘command and control system’ of all, body activities., It controls the following activities, (i) The voluntary movements and balance of the body., (ii) Functioning of vital involuntary organs, e.g. lungs, heart,, kidneys, etc., (iii) Thermoregulation, hunger and thirst., (iv) Circardian (24 hrs) rhythms of our body., (v) Activities of several endocrine glands and human, behaviour., (vi) It is also the site for processing of vision, hearing, speech,, memory, intelligence, emotions and thoughts., Location The brain is the anterior most part of the central, neural system, which is located in the cranium (cranial cavity), of the skull., Protective Coverings of the Brain It is covered by three, membranes or meninges (cranial meninges) present in the, cranial region of the skull. These membranes are as follows, (i) The outermost membrane, the duramater is the tough, fibrous membrane adhering close to the inner side of the, skull., (ii) The middle membrane, is very thin layer called arachnoid, membrane (arachnoid mater)., (iii) The innermost membrane, the piamater is thin, very, delicate, which is in contact with the brain tissue.

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Biology, Class 11th ( Term II ), , Practice Paper 2, , *, , (Unsolved), Time : 2 Hours, Max. Marks : 35, , General Instructions, , 1. There are 9 questions in the question paper. All questions are compulsory., 2. Question no. 1 is a Case Based Question, which has five MCQs. Each question carries one mark., 3. Question no. 2-6 are Short Answer Type Questions. Each question carries 3 marks., 4. Question no. 7-9 are Long Answer Type Questions. Each question carries 5 marks., 5. There is no overall choice. However, internal choices have been provided in some questions. Students have to attempt, only one of the alternatives in such questions., , * As exact Blue-print and Pattern for CBSE Term II exams is not released yet. So the pattern of this, paper is designed by the author on the basis of trend of past CBSE Papers. Students are advised, not to consider the pattern of this paper as official, it is just for practice purpose., , 1. Direction Read the following passage and answer the questions that follows., The heart is made up of cardiac muscles. The ventricular walls are thicker than that of the atrial walls. The, rhythm of heart is maintained by a highly specialised cardiac musculature called the nodal tissue distributed, evenly in the heart muscles., The figure given below shows a section of human heart with structures involved in the initiation and, transmission of electrical impulses during a heartbeat., , A, C, , B, , (i) Choose the correct labelling for A, B and C., A, (a) SA node, (b) AV node, (c) SA node, (d) AV node, , B, AV node, SA node, AV node, SA node, , C, Purkinje fibres, Bundle of His, Bundle of His, Purkinje fibres

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182, , CBSE Term II Biology XI, , (ii) Which of the following structures is also known as pacemaker?, (a) AV node, (c) Bundle of His, , (b) SA node, (d) Purkinje fibres, , (iii) Which of the given labelled structure is required for the transmission of depolarisation wave through the, ventricles?, (a) A, (c) C, , (b) B, (d) Both (a) and (b), , (iv) The technique that is used to identify a damage or defect in tissues of the heart is, (a) radiotherapy, (c) chemotherapy, , (b) ECG, (d) X-ray, , (v) The first heart sound occurs due to, (a) opening of semilunar valve, (c) onset of auricular systole, , (b) closing of semilunar valve, (d) sudden closure of AV valves, , 2. Give reasons for the following., (i) Plants are the lungs of nature., (ii) Chlorophyll-b and other accessory pigments are necessary for photosynthesis., (iii) In the high light intensities, the chlorophyll-a gets damaged., Or Two groups (A and B) or bean plants of similar size and same leaf area were placed in identical conditions., Group A was exposed to light of wavelength 400-450 nm and Group B to the light of wavelength of 500-550 nm., Compare the photosynthetic rate of the two groups by giving reason., , 3. What is the metabolic fates of pyruvic acid?, Or Which plant hormone can transform genetically dwarf plants into tall plants? State the mechanism involved, with suitable example., , 4. Which parts of the plants produce gibberellins? State two functions of this hormone and mention why it was, named gibberellin., Or Explain the reasons of following, (i) Photosynthesis can occur in the absence of light., (ii) Even non-green leaves can make the food., (iii) Photosynthesis can occur under water., , 5. Name the site (s) of pyruvate synthesis. Also, write the chemical reaction, wherein pyruvic acid dehydrogenase, acts as a catalyst., Or Why do cut leaves dipped in cytokinins stay green for longer duration?, , 6. What physiological circumtances lead to erythroblastosis foetalis?, 7. Why division of cell is important for us?, Or Explain, why a pair of homologous chromosomes is genetically different, but a pair of sister chromatids is, genetically identical before crossing over in meiosis., , 8. For maintenance of homeostasis the regulation of water and solute contents in the body is of prime importance., Describe how does the vertebrate kidneys performs this regulation., Or Describe the important steps in muscle contraction., , 9. How do gases (O 2 and CO 2 ) are transported in blood?, Or What is brain? Also describe the components of CNS with their functions., , Answers, 1. (i) (c), , (ii) (b), , (iii) (c), , (iv) (b), , (v) (d)

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Biology, Class 11th ( Term II ), , Practice Paper 3, , *, , (Unsolved), Time : 2 Hours, Max. Marks : 35, , General Instructions, , 1. There are 9 questions in the question paper. All questions are compulsory., 2. Question no. 1 is a Case Based Question, which has five MCQs. Each question carries one mark., 3. Question no. 2-6 are Short Answer Type Questions. Each question carries 3 marks., 4. Question no. 7-9 are Long Answer Type Questions. Each question carries 5 marks., 5. There is no overall choice. However, internal choices have been provided in some questions. Students have to attempt, only one of the alternatives in such questions., , * As exact Blue-print and Pattern for CBSE Term II exams is not released yet. So the pattern of this, paper is designed by the author on the basis of trend of past CBSE Papers. Students are advised, not to consider the pattern of this paper as official, it is just for practice purpose., , 1. Study the given figure of brain and answer the questions that follows, A, Forebrain, , C, , B, D, , (i) Which part is the largest and most complex of all the parts of the human brain?, (a) A, (c) C, , (b) B, (d) D, , (ii) Which of the following form the brain stem?, (a) Midbrain, (c) Forebrain, , (b) Hindbrain, (d) Both (a) and (b), , (iii) Which part of the brain control body temperature?, (a) A, (c) C, , (b) B, (d) D

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184, , CBSE Term II Biology XI, , (iv) The spinal cord is made up which of the following type of nervous tissues?, (a) Grey matter only, (c) Both (a) and (b), , (b) White matter only, (d) None of these, , (v) The structure which contains and protects the brain in vertebrate animals is, (a) cerebral aqueduct, (c) corpus callosum, , (b) cranium, (d) cerebral hemisphere, , 2. Glomerular filtrate and urine both are product of kidney function yet they differ from each other. Explain how?, Or Write a short note on, (i) coronary artery disease, (ii) angina pectoris, , 3. What conditions enable RuBisCO to function as an oxygenase?, Or How are gibberellins useful in agriculture to improve productivity? Give any three points in support of your, answer., , 4. Name the two important enzymes of C 3 and C 4 -pathways, respectively. What important role do they play in, fixing CO 2 ?, , 5. What are the roles played by antenna complex and photosystems in the process of photosynthesis?, Or Cyclic photophosphorylation results in the production of ATPs and not NADPH. Give reasons., , 6. Complete the following equation of conversion of pyruvic acid into acetyl coenzyme-A. Where does this process, occur inside the cell?, Mg 2+, , Pyruvic acid + Co-A + … → Acetyl Co-A + … + …, Pyruvate dehydrogenase, , 7. Explain meiosis-II in an animal cell., Or Write brief note on the following, (i) Synaptonemal complex, (ii) Metaphase plate, , 8. Terrestrial animals are generally either ureotelic not ammonotelic. Why?, Or (i) Androgen regulates the development, maturation and other important function in human male. List, them., (ii) Name the disorder/disease caused by, (a) Insufficient secretion of thyroid hormone in adults., (b) Insufficient amount of insulin secreted by pancreas., , 9. Give the transport of carbon dioxide as bicarbonate. Also explain chloride shift., Or Differentiate between, (i) Actin and myosin filament, (ii) A-band and I-band, (iii) Red muscle fibres and white muscle fibres, , Answers, 1. (i) (a), , (ii) (d), , (iii) (b), , (iv) (c), , (v) (b)