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Respiration in Plants, , , , Cellular respiration is an enzyme controlled process of, biological oxidation of food materials in a living cell, using, molecular O;, producing CO, and H,O, and releasing eneray, in small steps and storing it in biologically useful forms,, generally ATP., , , , , , So respiration is catabolic, exothermic and oxidative, , process,, , CohlyO;+60, "5 6CO, +6H,0+energy, hen catonitide Waler TATE), , , , Use of energy : Cellular activities like active transport,, muscle-contraction, bioluminescence, homothermy, locomotion,, nerve impulse conduction, cell division, growth, development, seed, germination require energy. Main source of energy for these, cendergonic activities in all living organisms including plants, comes, from the oxidation of organic molecules., , The energy released by oxidation of organic molecules is, actually transferred to the high energy terminal bonds of ATP, a, form that can be readily utilized by the cell to do work. Once ATP, is formed, its energy may be utilized at various places in the cell, to drive energy- requiring reactions. In these processes, one of, the three phosphate groups is removed from the ATP molecule., Thus the role of ATP as an intermediate energy transforming, compound between energy releasing and energy consuming, reactions., , , , , , Significance of respiration : Respiration plays a sig, role in the life of plants, The important ones are given below :, , (1) It releases energy, which is consumed in various metabolic, Processes necessary for life of plant., , (2) Energy produced can be regulated according to, requirement of all activities., , (3) It converts insoluble food into soluble form., , (4) Intermediate products of cell respiration can be used in, different metabolic pathways e.g.,, , ‘Acetyl CoA (in the formation of fatty acid, cutin and, + @- ketoglutaric acid (in the formation of glutamic, , , , isopren, , , , acid) ; Oxaloacetic acid (in the formation of aspartic, pyrimidines and alkaloids); Succinyl- CoA (synthesis of pyrrole, compounds of chlorophyll)., , (5) It liberates which is used in, , photosynthesis., , carbon dioxide,, , (6) Krebs cycle is a common pathway of oxidative breakdown, of carbohydrates, fatty acids and amino acids., , (7) It activates the different meristematic tissues of the plant., , CO, intake in photosynthesis balanced with CO, release in, respiration = Compensation point,, , Comparison between respiration and combustion =, According to Lavosier cell respiration resembles the combustion, (eg, buming of coal, wood, oil ete.) in the breakdown of complex, organic compounds in the presence of oxygen and production of, carbon dioxide and energy, but there are certain fundamental, differences between the two processes

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r ., , , , , , , , , , , , , , , , , , , , Table : 4.4-1, Differences between cell respiration and combustion, S.No. | Characters | Cell respiration Combustion, (i) | Natureof | Biochemical and | Physico-chemical, process stepped process. | and spontaneous, process,, (i) | Sie of Inside the cells, ‘Non-cellular., occurrence, (ii) | Controt Biological control! | Uncontrolled,, (i) | Energy Energy released in| Large amount of, release steps energy is released at, atime,, ()_[ Temperature | Remain within limits. | Rises very high,, (wi) | Light Nolight is produced. | Light may be, produced,, (wit) | Enzymes | Controlled by Not controlled by, enzymes. enzymes,, (vil) | intermediates | A number of No intermediate is, intermediates are | produced., produced., , , , , , , , , , Phases of respiration, There are three phases of respiration, , (1) External respiration : It is the exchange of respiratory, gases (O; and CO,) between an organism and its environment,, , , , (2) Internal or Tissue respiration : Exchange of, respiratory gases between tissue and extra cellular environment ., , Both the exchange of gases occur on the principle of diffusion., , (3) Cellular respiration : It is an enzymatically-controlled, stepped chemical process in which alucose is oxidised inside, the mitochondria to produce energy-rich ATP molecules with, high-energy bonds., , , , So, respiration is a biochemical process., Respiratory substrate or Fuel, , In respiration many types of high energy compounds are, oxidised. These are called respiratory substrate or respiratory fuel, and may include carbohydrates, fats and protein., , (1) Carbohydrate : Carbohydrates such as glucose, fructose, (hexoses), sucrose (disaccharide) or starch, insulin, hemicellulose, (polysaccharide) etc; are the main substrates, Glucose are the first, energy rich compounds to be oxidised during respiration. Brain, cells of mammals utilized only glucose as respiratory substrate., Complex carbohydrates are hydrolysed into hexose sugars before, being utilized as respiratory substrates. The energy present in one, gram carbohydrate is 4.4 Keal or 18.4 kd., , (2) Fats : Under certain conditions (mainly when, carbohydrate reserves have been exhausted) fats are also oxidised, Fat are used as respiratory substrate after their hydrolysis to fatty, acids and glycerol by lipase and their subsequent conversion to, hexose sugars, The energy present in one gram of fais is 9.8 Keal, or 41kJ, which is maximum as compared to another substrate., , , , Respiration in Plants 697, , The respiration using carbohydrate and fat as respiratory, substrate, called floating respiration (Blackmann)., , (3) Protein : In the absence of carbohydrate and fats ,, protein also serves as respiratory substrate. The energy present in, one gram of protein is : 4.8 Kal or 20 kJ. when protein are used, as respiratory substrate respiration is called protoplasmic, respiration,, , , , Types of respiratory organism, , , , Organism can be grouped into following four classes on the, basis of their respiratory habit., , (1) Obligate aerobes : These organisms can respire only in, the presence of oxygen. Thus oxygen is essential for their survival., , (2) Facultative anaerobes : Such organisms usually respire, aerobically (i.e., in the presence of oxygen) but under certain, condition may also respire anaerobically (e.g., Yeast, parasites of, the alimentary canal)., , (3) Obligate anaerobes : These organisms normally respire, anaerobically which is their major ATP- yielding process. Such, organisms are in fact killed in the presence of substantial amount of, ‘oxygen (e.9., Clostridium botulinum and C. tetani)., , (4) Facultative aerobes : These are primarily anaerobic, ‘organisms but under certain condition may also respire aerobically,, Types of respiration, , On the basis of the availability of oxygen and the complete or, incomplete oxidation of respiratory substrate. The respiration may, be either of the following two types : Aerobic respiration and, Anaerobic respiration, , Aerobic respiration, , It uses oxygen and completely oxidises the organic food, mainly carbohydrate (Sugars) to carbon dioxide and water. It, therefore, releases the entire energy available in glucose., , CoHti20, +60, —™_ 6CO, + 6H,0+ energy (686 Kecl), , , , is divided into two phases : Glycolysis, Aerobic oxidation of, pyruvic acid,, , Glycolysis / EMP pathway, , (1) Discovery : It was given by Embden, Meyerhof and, Parnas in 1930. It is the first stage of breakdown of glucose in, the cell., , (2) Definition : Glycolysis ( Gr. glykys= sweet, sugar; Iysis=, breaking) is a stepped process by which one molecule of glucose, (6c) breaks into two molecules of pyruvic acid (3c)., , (3) Site of occurrence : Glycolysis takes place in the, cytoplasm and does not use oxygen. Thus, it is an anaerobic, pathway. In fac, it occurs in both aerobic and anaerobic respiration.

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L Respiration in Plants 699, , , , , , , , , , , , , \—__- HPO,, , , , , , dehydrogenase ee SG, n=] Aconitase =, Fumarese ea, @ EE] I, ee aes E 120-H.0, Fag dehydrogenase Dg ata, @® [aeeainlewed tociie J NADH, _ at leet os dehydrogenase J,, a Gee thiokinace, , , , , , , Glutamic acid, , , , 4-2 Diagrammatic representation of oxidative decarboxylation of pyruvic acid and different chemical, oA., , reactions in Kreb's cycle starting from Acetyl C, , ‘Summary of Kreb's cycle, , (i) All the enzymes, reactants, intermediates and products of, TCA cycle also are found in aqueous solution in the matrix, except, the succinate dehydrogenase (mitochondrial marker enzyme), which is located in the inner mitochondrial membrane., , (ii) Oxidation of one mole of acetyl CoA uses 4 molecules of, water and releases one molecule of water., , (iii) Liberates 2 molecules of carbon dioxide., , {iv) Gives off 4 pairs of hydrogen atoms., , , , (v) Produces one GTP/ ATP molecule during the formation of, succinate,, , (vi) One mole of acetyl CoA gives 12 ATP during oxidation in, Krebs cycle., , (vii) Regenerates oxaloacetate used in last cycle for reuse., , ‘The above summary is for one molecule of acetyl coenzyme, ‘A, There are two acetyl coenzyme A molecules formed from one, molecule of glucose by glycolysis and oxidative decarboxylation of, pyruvate,