More from Arunavasir (AC)

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Chapter –2, , Sexual Reproduction, in Flowering Plants, , 1. Parts of Flower, QQ, , In a flower, four different sets of whorls or floral members are attached to a central axis called, thalamus., , QQ, , The outermost and the first accessory whorl is of sepals and is called calyx., , QQ, , The second accessory whorl is of petals and is called corolla., , QQ, , Next to the corolla, is the male reproductive whorl of stamens called androecium., , QQ, , The female reproductive whorl is of carpels and is called gynoecium or pistil., , QQ, , Calyx and corolla are the non-essential whorls while androecium and gynoecium are the essential, whorls., Stigma, Style, , Petal, Anther, , Pistil, , Stamen, , Filament, Sepal, , Ovary, , Ovule, , Thalamus, , Fig. 2.1 A diagrammatic representation of L.S. of a flower, , 2. Functions of Floral Members, QQ, , Calyx, (i) Its main function is to protect the flower in bud condition. It is smaller than the petals in size., (ii) When green, it is photosynthetic in nature., (iii) When coloured, it attracts insects for pollination., , Sexual Reproduction in Flowering Plants 27

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Corolla, , QQ, , (i) It provides colour and scent to attract pollinators., (ii) Sometimes the base of corolla bears some secretory glands and secretes nectar., (iii) They also provide protection to the plant., Androecium: Its main function is the production of microspores, i.e., pollen grains containing male, gametes within the anther lobe., , QQ, , Gynoecium: The function of gynoecium is the production of megaspores eggs, fruits and seeds., , QQ, , 3. Male Reproductive Unit, Stamen is the male reproductive unit and consists of the following two parts:, , QQ, , (i) A long and slender stalk called filament., (ii) A bilobed terminal structure called anther., , Structure of Anther, QQ, , It is composed of two anther sacs or lobes separated by a tissue called connective tissue., , QQ, , The anther is bilobed and each lobe or sac consists of two theca separated by a septum., The anther is a tetragonal (four-sided) structure, consisting of four microsporangia, two in each of, the lobes., , QQ, , Microsporangia develop and get transformed into pollen sacs., , QQ, , (a), , (b), , Fig. 2.2 (a) A typical stamen; (b) Transverse section of an anther, , Structure of Microsporangium, QQ, , A typical microsporangium appears circular and is surrounded by four walls:, (i) Epidermis: It is the outermost single layer of cell which is protective in nature., (ii) Endothecium: It is the second layer with thick cells, help in dehiscence and is protective in, nature., (iii) Middle layer: It is the third layer composed of 1−3 layers of cells, help in dehiscence and is, protective in nature., (iv) Tapetum: It is the fourth and innermost layer of cell with dense cytoplasm and many nuclei. It, provides nourishment to the developing pollen grains., , QQ, , 28, , The centre of each microsporangium is filled with closely arranged similar cells called sporogenous, cells.

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QQ, , At maturity, pollen sac is formed by fusion of two microsporangium in each lobe., , QQ, , A mature anther dehisces by slits and liberate the pollen grains., , Microspore, mother cells, , (a), , , , (b), , Fig. 2.3 (a) Transverse section of a young anther;, (b) Enlarged view of one microsporangium showing wall layers, , Microsporogenesis, QQ, , The process of formation of microspore from a pollen mother cell by meiosis is called microsporogenesis., , Connective tissue, , Fig. 2.4 T.S. of mature dehisced anther with pollen grains, QQ, , QQ, QQ, , Each cell of the sporogenous tissue in a microsporangium acts as a potential pollen mother cell, (PMC) or microspore mother cell., PMC undergoes meiotic divisions to form cluster of four cells called microspore tetrad., On maturity, the anther dehydrates and the microspores separate from each other to form pollen, grains with two layered wall—outer hard exine and inner intine., , Pollen Grains, QQ, , Pollen grains are generally spherical in structure., , QQ, , They possess two prominent wall layers—outer exine and inner intine., , Sexual Reproduction in Flowering Plants 29

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The exine is a hard layer made of sporopollenin which is one of the most resistant organic material, present in nature. It can withstand high temperature and strong acids and alkalis. Even enzymes, cannot degrade sporepollenin and hence pollens are preserved as fossils., , QQ, , QQ, , The inner thin layer of intine is made up of cellulose and pectin., , QQ, , The exine has aperture where sporopollenin is absent, called germ pores., , QQ, , The newly differentiated pollen grain has a central nucleus and dense cytoplasm., , QQ, , Pollen grain is the first cell of a male gametophyte., The protoplast increases in size and mitotically divides into two unequal cells—(a) bigger vegetative, cell which is rich in food reserve and large irregularly shaped nucleus, and (b) smaller spindle-shaped, generative cell with dense cytoplasm and a nucleus. This is called the 2-celled stage., , QQ, , In majority angiosperms, pollens are released in this 2-celled stage, whereas in other species, the, generative cell divides into 2 male gametes and thus pollen is said to be in 3-celled stage., , QQ, , Meiosis, , Microspore/, Pollen mother cell, , Microspore tetrad, , Microspore separated, , (a), , Generative cell, Vegetative, cell, , Mitosis, , 2 male, gametes, , (b), , Vegetative, cell, Mature pollen grain, (2-celled pollen), , 3-celled pollen, (in some plant species), , Fig. 2.5 (a) Enlarged view of a pollen grain tetrad;,       (b) Stages of a microspore maturing into a pollen grain, , Importance of pollen grains, OO, , They contain male gametes for sexual reproduction., , OO, , These are nutrient-rich and thus are taken as food supplements., , OO, , OO, , Pollens can be stored for years in liquid nitrogen at –196°C, to be used later in crop breeding, programmes., They may cause allergies and bronchial afflictions in some people leading to asthma,, bronchitis, etc., , 4. Female Reproductive Unit, QQ, QQ, , 30, , The pistil or gynoecium represents the female reproductive unit of a flower., The gynoecium may have single pistil (called monocarpellary), more than two pistils (called, multicarpellary), fused pistils (called syncarpous) or free pistils (called apocarpous).

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Free, carpels, , (a), , (b), , (c), ,   Fig. 2.6 (a) Pistil of Hibiscus; (b) Multicarpellary, syncarpous pistil of Papaver;,     (c) A multicarpellary, apocarpous gynoecium of Michelia, , Table 2.1: Parts of pistil and their functions, S. No., , Parts, , Functions, , (i), , Stigma, , It receives the pollen grains. It has sticky surface and pollen grains get stuck to it, during pollination., , (ii), , Style, , It is an elongated slender part beneath the stigma, that connects the stigma with, ovary. It holds the stigma to receive the pollen grains. It is through the style that the, pollen tube grows and reaches the ovule., , (iii), , Ovary, , It is the basal swollen part of pistil that contains ovules and eggs., , QQ, , Inside the ovary there is a compartment called ovarian cavity or locule separated by septum., , QQ, , Placenta is the tissue in ovarian cavity from where ovule or megasporangium arise., , Structure of Megasporangium (Ovule), QQ, QQ, , The ovule is stalked and is attached to the placenta by means of a stalk called funicle., The junction between an ovule and a funicle is called hilum. Sometimes, the funicle extends beyond, the hilum to form a ridge called raphae., , QQ, , The ovule is surrounded by one or two protective multicellular integuments., , QQ, , Integument encircles the ovule entirely except at the tip, resulting in a small opening called micropyle., , QQ, , The basal part of an ovule opposite to micropyle is called chalaza., , QQ, , The cells with high or abundant reserve food material enclosed within integument is called nucellus., , QQ, , The female gametophyte located within the nucellus is called an embryo sac., , Sexual Reproduction in Flowering Plants 31

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Chalaza, Outer, integument, Nucellus, Inner, integument, Antipodal cells, Central cell, Embryo sac, , Polar nuclei, , Egg (Oosphere), Synergids, Vascular strand, Integuments, Micropyle, , Hilum, Funiculus, , Fig. 2.7 A diagrammatic view of a typical anatropous ovule, , Megasporogenesis, The process of formation of haploid megaspores from the diploid megaspore mother cell (MMC) is, called megasporogenesis., , QQ, , In the micropylar region, the nucellus contains cells with dense cytoplasm and prominent nucleus, which is differentiated into a single MMC., , QQ, , QQ, , MMC is diploid and undergoes meiosis., , QQ, , MMC first divides transversely into two cells called dyad., These two cells again divide transversely, as a result a linear row of four haploid cells is produced, which is called megaspore tetrad or linear tetrad., , QQ, , Out of these four megaspores, only one remains functional while the other three degenerate., , QQ, , The one functional megaspore develops into the female gametophyte or embryo sac. This is called, monosporic development., , QQ, , Megagametogenesis, QQ, , The formation of female gametophyte (embryo sac) is called megagametogenesis., (i) Megaspore is the first cell of the female gametophyte., (ii) The megaspore increases in size and its nucleus divides mitotically into two nuclei which move, apart to opposite poles. Thus, a 2-nucleate embryo sac is formed., (iii) The two daughter nuclei undergo another mitotic division giving rise to the 4-nucleate stage., (iv) The third mitotic division gives rise to 8-nucleate 7-celled embryo sac., (v) The central cell contains 2 nuclei known as polar nuclei., (vi) The three nuclei at the micropylar region form the egg apparatus., (vii) In the egg apparatus, the middle cell is the largest and is called oosphere/egg/ovum, while, other two naked cells adjoining the egg cell are called synergids., , 32

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(viii) The three nuclei at the chalazal end are surrounded by cytoplasm and cellular wall. These are, called antipodal cells., (ix) Female gametophyte is 7 celled, 8 nucleate as it consist of 7 cells but 8 nuclei (2 nuclei in polar, cell)., , (a), , (b), (c), Fig. 2.8 (a) Parts of the ovule showing a large megaspore mother cell, a dyad and a tetrad of megaspores;, (b) 2, 4 and 8-nucleate stages of embryo sac and a mature embryo sac;, (c) A diagrammatic representation of the mature embryo sac, , 5. Pollination, QQ, , The transfer of pollen grains from anther and their deposition over stigma of the pistil is termed as, pollination. Depending upon sources of pollen grains, pollination is of three types., , Autogamy, 1. The transfer of pollen grains is, from anther to stigma of the, same flower, e.g., pea, rice,, wheat, etc. It is self-pollination., 2. Brings pollen with similar, genetic constitution on stigma., , Geitonogamy, 1. The transfer of pollen grains is, from anther of one flower to the, stigma of another flower of, same plant, e.g., Cucurbita., 2. It is functionally cross-pollination, but genetically similar to, autogamy., , Xenogamy/Allogamy, 1. The transfer of pollen grains is, from anther of one flower to the, stigma of another flower of, different plant, e.g., Papaya,, maize., 2. Brings genetically different, types of pollen grains to stigma., , Sexual Reproduction in Flowering Plants 33

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Contrivances or Devices for Self-pollination (Autogamy), Cross-pollination can be prevented by exhibiting, , QQ, , (i) Cleistogamous flowers: These are bisexual closed flowers which never open and the anthers, dehisce inside these closed flowers, e.g., Commelina and produce seed set even in absence of, pollinators., (ii) Homogamy: It is the condition of the maturity of anther and stigma at the same time, i.e.,, synchrony in pollen release and stigma receptivity. e.g., Catharanthus (Vinca)., (iii) Close association between anther and stigma, e.g., Mirabilis., , Advantages of Self-pollination, (i) Pure breed of parents is maintained., (ii) Large numbers of pollen grains are not required for pollination., (iii) Seed production is ensured., (iv) Plants do not need to develop mechanisms for attracting pollinators., , Disadvantages of Self-pollination, (i) Variations are not introduced in the progeny., (ii) Vitality of the breed decreases with time., (iii) Adaptability to changing environment is reduced., , Contrivances or Devices for Cross-pollination (Xenogamy/Allogamy), QQ, , Self-pollination can be prevented by exhibiting, (i) Dicliny or Unisexuality: Male and female flowers are separate. Dioecious condition is seen in, papaya., (ii) Dichogamy: The condition in which the stamens and stigma of a bisexual flower mature at, different times. It is of two types:, , (a) Protandry: This is the condition where anthers mature earlier than the stigma and release, pollens., (b) Protogyny: This is the condition where the stigma matures earlier than the anther., (iii) Self-sterility or self-incompatibility: It is a genetic mechanism that prevents self-pollination., Pollen grains of a flower do not germinate on stigma of same flower due to similar sterile genes., (iv) Chasmogamous flowers: These are open flowers with exposed stamens and stigma which, facilitate cross-pollination., , Advantages of cross-pollination:, (i) Variation in the progeny is introduced through recombination., (ii) The progenies have better adaptability to changing environment., (iii) Plants develop new traits like disease resistance., (iv) The defective characters are eliminated over the generations., , Disadvantages of cross-pollination:, (i) Large numbers of pollen grains need to produced of which most are lost during the process of, pollination., (ii) There is always a chance that pollination may not occur., (iii) It is less economical., , 34

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Adaptation for Water Pollination/Hydrophily, QQ, , QQ, , QQ, , QQ, , QQ, , The form of pollination in which pollens are, distributed by water is called hydrophily., It is very common in algae, bryophytes,, pteridophytes and some angiosperms., Vallisneria and Hydrilla are submerged, freshwater hydrophytes in which hydrophily is, observed., In sea-grasses (e.g., Zostera), female flowers are, submerged in water to receive pollen grains, for pollination inside water. Pollens are long,, needle-like and are carried passively by water., , Fig. 2.9 Pollination by water in Vallisneria, , In Vallisneria, the female flower stalk is long to, reach the water surface to receive the pollen grains carried by water currents and the stalks coil up, after pollination., , QQ, , Pollen grains are protected from wetting by the presence of a mucilaginous covering., , QQ, , Flowers are not very colourful and do not produce nectar., , Adaptation for Wind Pollination/Anemophily, QQ, , The form of pollination in which wind distributes the pollens is called anemophily., , QQ, , Pollen grains are light in weight, non-sticky, dry and may be winged as in Pinus., , QQ, , Stamens are well-exposed for easy dispersal of pollen grains in the wind., , QQ, , The stigma is sticky, large and feathery to trap pollen grains floating in the air, e.g., tassels in corn cob., , QQ, , Numerous flowers are packed together to form inflorescence., , QQ, , Single ovule is present in each ovary. Flowers are not very colourful and do not produce nectar., , Fig. 2.10 A wind-pollinated plant showing, compact inflorescence and well-exposed stamens, , Fig. 2.11 Insect pollination, , Adaptation for Insect Pollination/Entomophily, QQ, , The form of pollination in which insects distribute pollens is called entomophily., , QQ, , Flowers are large, sticky and brightly coloured., , QQ, , If small, number of flowers are clustered into inflorescence to make them conspicuous., , QQ, , They have honey and nectar glands, which are highly fragrant to attract insects., , QQ, , The pollen grain surface is sticky due to exine layer and stigma is sticky due to mucilaginous secretion., , QQ, , The flowers offer floral rewards like nectar and pollen grains for pollination to insects., , Sexual Reproduction in Flowering Plants 35

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QQ, , In some species, floral rewards provide safe place to lay eggs, e.g., Amorphophallus., , QQ, , The flower sometimes secrete foul odour to attract insects like flies and beetles., , 6. Pollen−Pistil Interaction, QQ, , All the events from pollen deposition on the stigma until the entry of the pollen tubes into the ovule, are together called pollen–pistil interactions., , (Secondary nucleus), , Hilum, (a), , (b), , (c), , Fig. 2.12 (a) L.S. of pistil showing path of pollen tube growth;, (b) Enlarged view of an egg apparatus showing entry of pollen tube into a synergid;, (c) Discharge of male gametes into a synergid and the movements of the sperms, one into the egg and the, other into the central cell, QQ, QQ, , It is a dynamic process involving pollen recognition by stigma/pistil for compatible pollen., Incompatible pollens or sterile pollens are rejected by the pistil and do not allow growth of pollen, tube., , QQ, , Compatible pollens are encouraged by pistil for growth and development of pollen tubes., , QQ, , The pollen tube grows through stigma and style to reach the ovary., , QQ, , It then enters the ovule through micropyle and reaches the synergids, guided by filiform apparatus., , 7. Artificial Hybridisation, QQ, QQ, , QQ, , QQ, , Commonly used technique in plant breeding programmes to obtain desirable characters., Anthers are removed from the bisexual flowers using forceps. This is emasculation and is done, before the anther dehisces., The emasculated flower is covered with a paper bag to prevent contamination from unwanted, pollens. This is called bagging., On attaining maturity, mature pollens from desirable plant are dusted on stigma of bagged flower, and rebagged for fruit development., , 8. Double Fertilisation/Triple Fusion, QQ, QQ, , QQ, , 36, , On reaching synergid, pollen tube releases the two male gametes into cytoplasm of synergid., One of the male gamete fuses with egg nucleus to form a diploid cell called zygote. This event is, called syngamy., Other male gamete fuses with polar nuclei at the centre to produce a triploid primary endosperm, nucleus (PEN). This is termed as triple fusion.

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QQ, , QQ, , QQ, , As syngamy and triple fusion take place simultaneously in the embryo sac, it is termed as double, fertilisation., The central cell after triple fusion forms primary endosperm cell (PEC) which later develops into, endosperm., The zygote later develops into an embryo., , 9. Post-fertilisation Events, QQ, , The following events after double fertilisation are collectively called post-fertilisation events:, (i) Development of endosperm from primary endosperm nucleus (PEN), (ii) Development of embryo from zygote, (iii) Development of seeds from ovule, (iv) Development of fruit from ovary, , Endosperm Development, QQ, , Endosperm develops first, followed by an embryo., , QQ, , Endosperm develops from PEN., , QQ, , QQ, , PEN undergoes successive nuclear divisions to give rise to free nuclei and this stage of endosperm, development is called free nuclear endosperm., Subsequently, cell wall is formed on the periphery and endosperm becomes cellular. It is now called, cellular endosperm., , Functions, (i) The cells of endosperm tissue are triploid and filled with reserve food material to nourish the, developing embryo., (ii) The water of tender coconut in the centre is free-nuclear endosperm and white kernel in the, outer part is the multicellular endosperm., (iii) The endosperm may be completely consumed by the developing embryo, e.g., pea, beans, or it, may persist in mature seed, e.g., coconut., , Embryo Development, QQ, , Early development of embryo from the zygote is called embryogeny., , QQ, , Embryo develops from zygote at the micropylar end of embryo sac., , QQ, , The nutrition for development is provided by endosperm., , QQ, , The zygote divides mitotically to form proembryo., , QQ, , The different stages of the developing proembryo are globular and heart-shaped embryo, which, finally forms mature embryo., , Embryogeny in Dicots, QQ, QQ, , QQ, , QQ, , The zygote undergoes transverse division forming a large basal cell and a small apical or terminal cell., The large basal cell enlarges and undergoes transverse division to from a group of 6–10 cells called, suspensor., The first cell of the suspensor towards the micropylar end is called haustorium, whereas the last cell, of the suspensor towards the chalazal end is called hypophysis that later develops into radicle., The smaller terminal or apical cell undergoes one vertical division. The two cells formed from, terminal cell divide by a transverse division thus forming four embryonal cell (quadrant stage)., , Sexual Reproduction in Flowering Plants 37

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Basal, cell, Apical, cell, , Mature dicot embryo, (a), , (b), , (c), , (i), , (ii), , (iii), , (iv), , (v), , (vi), , (vii), , (viii), , Scutellum, Coleoptile, Shoot apex, Epiblast, , Radicle, Root cap, Coleorrhiza, (d), , Mature monocot embryo, , Fig. 2.13 (a) Fertilised embryo sac showing zygote and primary endosperm nucleus (PEN);, (b) Stages in embryo development in a dicot [shown in reduced size as compared to (a),    (c) Mature dicot embryo,    (d) Stages in embryo development in a monocot, , QQ, , 38, , Finally these four cells divide vertically forming 8-celled proembryo (octate stage). Four cells at the, apex give rise to plumule and another four give rise to hypocotyl except its tip.

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Structure of dicotyledonous embryo, (i) A typical dicotyledonous embryo consists of an embryonal axis, and two cotyledons., (ii) The portion of embryonal axis above the level of cotyledon is, called epicotyl, which develops into plumule or baby shoot, (future shoot)., (iii) The cylindrical portion below the level of cotyledon is the, hypocotyl, which develops into radicle or root tip (future root)., (iv) The root tip is often covered with a root cap (calyptra)., , Fig. 2.14 A typical dicot embryo, , (v) Mango, apple, radish, rose, etc., are some dicot plants., , Structure of monocotyledonous embryo, (i) A typical monocotyledonous embryo consists of one cotyledon., (ii) The cotyledon is situated on one side (lateral) of the embryonal axis and is called scutellum., (iii) The radicle and root cap are situated at the lower end of embryonal axis in an undifferentiated, sheath called coleorhiza., (iv) The shoot apex and few leaf primordia are enclosed in a hollow foliar structure in epicotyl, region called coleoptile., (v) The portion of the embryonal axis above the level of attachment of scutellum is called epicotyl., (vi) Grass, banana, bamboo, palm, etc., are some monocot plants., , Seed Development, QQ, , Seed is a fertilised ovule which is the final product of sexual reproduction., , QQ, , It consists of the following:, (i) Seed coat(s): 1–2 in number, having an opening called micropyle. Outer integument forms, outer seed coat (testa) and inner integument forms inner seed coat (tegmen)., (ii) Cotyledons: 1–2 in number and rich in reserve food material., (iii) Embryonal axis, , (Non-endospermous), , QQ, QQ, , (Endospermous), , Sometimes in the seed, nucellus may persist. This is called perisperm, e.g., in black pepper., With maturity, the water content of seed decreases and finally enters a state of inactivity called, dormancy., , Advantages of seeds, (i) Seeds posses better adaptive strategies for dispersal to form a new colony., (ii) The reserve food of seed support the growth of seedling till they become nutritionally, independent., (iii) The hard seed coats (testa + tegmen) provide protection against injury., (iv) They provide genetic recombination and variation as they are the product of sexual reproduction., (v) Seeds are stored to be consumed throughout the year, to overcome drought and natural calamities., (vi) Depending upon the mobility of seeds, they are used to raise crop in favourable season., , Sexual Reproduction in Flowering Plants 39

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(a), , (b), , (d), , (c) Onion, , Fig. 2.15 Structure of some seeds, , Fruit Development, QQ, QQ, , The ovary matures to form fruit and the ovarian wall develops into the fruit wall called pericarp., Fruits can be, (i) Fleshy, e.g., orange, mango, etc., (ii) Dry, e.g., mustard, groundnut, etc., , Fruit that develops only from ovary, e.g., pea, wheat, ,maize., , QQ, , Fruit that develops from ovary and the thalamus, or other part of flower, e.g., apple, strawberry., , Fruits consist of three parts: (a) outer skin called epicarp, (b) middle flesh called mesocarp, (c) innermost, part called endocarp, , Epicarp, (a), , Fig. 2.16 False fruits of apple and strawberry, , 40, , (b)

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Parthenocarpic Fruit, QQ, , Fruits that are formed without fertilisation are called parthenocarpic fruits. These do not have seeds,, e.g., banana. Parthenocarpy can also be induced artificially by growth hormones., , Embryo sac, in ovule, , Fig. 2.17 Summary of fruit formation that includes germination of a seed, vegetative growth and, the production of flowers that eventually bear fruit, which contains seeds, , 11. Special Mechanisms of Reproduction, (i) Apomixis, OO, , OO, , The phenomenon of asexual reproduction that imitates sexual reproduction by formation of, seed without fertilisation is called apomixis or agamospermy., Ways of development of apomictic seeds:, , (a) A diploid egg is formed without reduction division and develops into embryo without, fertilisation., (b) Some cells of the nucellus, which are diploid in nature, start dividing and without fertilisation, develop into embryo, e.g., citrus fruits and mango., , (ii) Polyembryony, OO, , The occurrence of more than one embryo in a seed is called polyembryony, e.g., orange., , OO, , Ways of forming polyembryonic seeds:, , (a) Development of cells like synergids, cells of nucellus, cells of integument, into embryo., (b) Formation of more than one embryo sac in an ovule., (c) Formation of more than one egg in an embryo sac., , Sexual Reproduction in Flowering Plants 41

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NCERT Textbook Questions, Q. 1. Name the parts of an angiosperm flower in which development of male and female gametophyte, take place., Ans. Development of male and female gametophytes takes place in anther and ovary, respectively., Q. 2. Differentiate between microsporogenesis and megasporogenesis. Which type of cell division, occurs during these events? Name the structures formed at the end of these two events., Ans., Table 2.2: Differences between microsporogenesis and megasporogenesis, S. No., , Microsporogenesis, , Megasporogenesis, , (i), , In this process, haploid microspores are, formed from diploid microspore mother cell, or pollen mother cell (MMC or PMC)., , In this process, haploid megaspores are, formed from diploid megaspore mother cell, (MMC)., , (ii), , It occurs inside the microsporangia or pollen, sac of an anther., , It occurs inside the nucellus of ovule or, megasporangium., , (iii), , There are many microspore mother cells in a, microsporangium., , There is generally a single megaspore mother, cell in a megasporangium., , (iv), , The four microspores formed from a single, microspore mother cell are generally arranged, in a tetrahedral structure., , The four megaspores formed from a, megaspore mother cell are arranged in the, form of a linear tetrad., , (v), , All the four microspores arranged in a, tetrahedral tetrad are functional., , Only one megaspore remain functional while, the other three degenerates., , (vi), , The microspores, gametophyte., , The functional megaspore gives rise to female, gametophyte., , give, , rise, , to, , male, , Meiosis occurs during micro- and megasporogenesis. Microspores (pollen grains) are formed, at the end of microsporogenesis and female gametophyte (embryo sac) are formed at the end of, megasporogenesis., Q. 3. Arrange the following terms in the correct developmental sequence: pollen grain, sporogenous, tissue, microspore tetrad, pollen mother cell, male gametes., Ans. Sporogenous tissue, Pollen mother cell, Microspore tetrad, Pollen grain, Male gametes., Q. 4. With a neat, labelled diagram, describe the parts of a typical angiosperm ovule., Ans. For diagram, refer to Fig. 2.7., Refer to Basic Concepts Point 3 (Structure of Megasporangium)., Q. 5. What is meant by monosporic development of a female gametophyte?, Ans. Out of the four megaspores, three degenerate and only one remains functional which develops, into a female gametophyte or embryo sac. This is called monosporic development, i.e., when, embryo sac develops from one single megaspore it is called monosporic embryo sac., Q. 6. With a neat diagram and explain the 7-celled, 8-nucleate nature of the female gametophyte. , , [CBSE Delhi 2017], Ans. Female gametophyte or embryo sac is a small oval structure that contains a 3-celled egg apparatus,, 3 antipodal cells and one binucleate central cell hence, it is 7-celled and 8-nucleate structure., (i) Egg apparatus: It consists of two synergids and an egg cell towards the micropylar end. The, cells of egg apparatus are uninucleate. Synergids towards its micropylar end have cellular, thickenings called filiform apparatus that helps in guiding pollen tube into the synergids., (ii) Antipodal cells: Chalazal end of embryo sac contain three cells of various shapes and sizes, called antipodal cells., (iii) Central cell: It is the single and largest cell which is bounded by a membrane of embryo, sac. It contains two polar nuclei which later fuse to form diploid secondary nucleus. After, fertilisation the central cell gets converted into triploid primary endosperm cell (PEC) which, forms endosperm., For diagram, refer to Fig. 2.8(c)., , 42

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Q. 7. What are chasmogamous flowers? Can cross-pollination occur in cleistogamous flowers? Give, reasons for your answer., Ans. Chasmogamous flowers are open flowers with exposed stamens and stigma which facilitate, cross-pollination., No cross-pollination occurs in cleistogamous flowers as these flowers are closed and never open, and thus no transfer of pollen from outside to stigma of the flower is possible., Q. 8. Mention two strategies evolved to prevent self-pollination in flowers., Ans. The two strategies evolved to prevent self-pollination in flowers are:, (i) Maturation of anthers and stigma at different time periods in a bisexual flower prevents selfpollination (dichogamy)., (ii) Production of unisexual flowers., Q. 9. What is self-incompatibility? Why does self-pollination not lead to seed formation in selfincompatible species?, Ans. Self-incompatibility or self sterility is the inability of an intersexual or bisexual plant to produce, viable seeds on self-pollination, in spite of producing functional male and female gametes. Since,, fertilisation does not take place, no seeds are produced. It is a genetic mechanism that prevents, self pollen from fertilizing ovules by inhibiting pollen tube growth in pistil., Q. 10. What is bagging technique? How is it useful in a plant breeding programme?, Ans. It is the covering of female plant with butter paper germ to avoid their contamination from, foreign pollens during breeding programme., Q. 11. What is triple fusion? Where and how does it take place? Name the nuclei involved in triple fusion., Ans. Triple fusion is fusion of one male gamete and two polar nuclei (or secondary nucleus; if the two, have already fused) in the central cell of embryo sac to form primary endosperm nucleus., It takes place in the central cell of an embryo sac. Three nuclei are involved in triple fusion, i.e.,, one male nucleus and two polar nuclei in the central cell., Q. 12. Why do you think the zygote is dormant for sometime in a fertilised ovule?, Ans. The zygote is dormant for sometime in a fertilised ovule because the embryo which is developed, from zygote may obtain nutrition from endosperm., Q. 13. Differentiate between:, (a) hypocotyl and epicotyl, (b) coleoptile and coleorhiza, (c) integument and testa, (d) perisperm and pericarp., Ans. (a), Table 2.3: Differences between hypocotyl and epicotyl, S. No., , Hypocotyl, , Epicotyl, , (i), , The region of the embryonal axis that, lies between the radicle and the point of, attachment of cotyledons is called hypocotyl., , The region of the embryonal axis that lies, between the plumule and cotyledons is called, epicotyl., , (ii), , Hypocotyl pushes the seed above the soil, in epigeal germination., , Epicotyl pushes the plumule above the soil in, hypogeal germination., , (iii), , It is an important component of embryonic, root system., , It is an important component of embryonic, shoot system., , (b), , Table 2.4: Differences between coleoptile and coleorhiza, S. No., , Coleoptile, , Coleorhiza, , (i), , The shoot apex and few leaf primordia, are enclosed in a hollow foliar structure in, epicotyl region in monocots and is called, coleoptile., , The radicle and root cap are situated at the, lower end of embryonal axis are enclosed by, undifferentiated sheath called coleorhiza., , (ii), , It comes out of the soil., , It remains inside the soil., , (iii), , It emerges from the soil, turns green and, carries out photosynthesis., , It remains in the soil and is non-green in, colour., , Sexual Reproduction in Flowering Plants 43

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(c), , Table 2.5: Differences between integument and testa, S. No., , Integument, , Testa, , (i), , It is the protective covering of the ovule It is the protective covering of the seed., (nucellus)., , (ii), , It is thin and living., , It is thick and dead., , (iii), , It is part of pre-fertilisation., , It is part of post-fertilisation., , (d), , Table 2.6: Differences between perisperm and pericarp, S. No., , Perisperm, , Pericarp, , (i), , It represents persistent remains of nucellus It represents the wall of fruit formed by the, (of ovule) in the seed., ovarian wall., , (ii), , It is a part that belongs to seed., , It is a part that belongs to fruit., , (iii), , It is usually dry., , It can be dry or fleshy., , Q. 14. Why is apple called a false fruit? Which part(s) of the flower forms the fruit?, Ans. False fruits are those fruits in which accessory floral parts also contribute to fruit formation. In, apple, the thalamus also contributes to fruit formation. Therefore, it is called a false fruit. The fruit, develops from the ovary of the flower., Q. 15. What is meant by emasculation? When and why does a plant breeder employ this technique?, Ans. Emasculation is a practice of removal of stamens/anthers before the anther dehisces from bisexual, flowers in female parent. A plant breeder employs this technique in the bud condition before the, anthers begin to differentiate. It is required to prevent self-pollination., Uses in plant breeding:, (i) Prevention of contamination and pollination of stigma of female flowers with foreign, undesirable pollens., (ii) Prevention of damage by animals., Q. 16. If one can induce parthenocarpy through the application of growth substances, which fruits, would you select to induce parthenocarpy and why?, Ans. Only fleshy fruits like orange, watermelon, lemon, etc., should be selected as parthenocarpic, fruits. Here seeds of fruits are irritant during consumption so seeds are removed so as to make, the fruits even more valuable. It is easy to make fruit juices, jams, etc. with seedless fruits., Q. 17. Explain the role of tapetum in the formation of pollen grain wall., Ans. Tapetum is the innermost wall layer of a microsporangium. It nourishes the developing pollen, grains and also help in the formation of wall of pollen grains. The cells of tapetum secrete Ubisch, granules that provide sporopollenin and other materials for exine formation., Q. 18. What is apomixis and what is its importance?, Ans. Apomixis is a type of asexual reproduction that mimics sexual reproduction to form seeds, without fertilisation., In apomictic seeds, parental characters are maintained in the progeny/offspring as there is no, meiosis or segregation of characters., If desired hybrid seeds are made apomictics the farmers can keep on using the hybrid seeds to, raise new crops year after year., , Multiple Choice Questions, Choose and write the correct option in the following questions., 1. In a cereal grain, the single cotyledon of embryo is represented by, (a) coleoptile , (b) coleorhiza, (c) scutellum , (d) hypocotyl, , 44, , [1mark]

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2. In a typical complete, bisexual and hypogynous flower the arrangement of floral whorls on the, thalamus from the outermost to the innermost is, [NCERT Exemplar], (a) calyx, corolla, androecium and gynoecium (b) calyx, corolla, gynoecium and androecium, (c) gynoecium, androecium, corolla and calyx (d) androecium, gynoecium, corolla and calyx, 3. A dicotyledonous plant bears flowers but never produces fruits and seeds. The most probable, cause for the above situation is , [NCERT Exemplar], (a) plant is dioecious and bears only pistillate flowers, (b) plant is dioecious and bears both pistillate and staminate flowers, (c) plant is monoecious, (d) plant is dioecious and bears only staminate flowers., 4. In angiosperms, male gametes are formed by the division of, (a) microspore mother cell , (b) microspore, (c) generative cell , (d) vegetative cell, 5. During microsporogenesis, meiosis occurs in, [NCERT Exemplar], (a) endothecium , (b) microspore mother cells, (c) microspore tetrads , (d) pollen grains., 6. From among the sets of terms given below, identify those that are associated with the, gynoecium. , [NCERT Exemplar], (a) Stigma, ovule, embryo sac, placenta, (b) Thalamus, pistil, style, ovule, (c) Ovule, ovary, embryo sac, tapetum, (d) Ovule, stamen, ovary, embryo sac, 7. Starting from the innermost part, the correct sequence of parts in an ovule are , , [NCERT Exemplar], (a) egg, nucellus, embryo sac, integument, (b) egg, embryo sac, nucellus, integument, (c) embryo sac, nucellus, integument, egg, (d) egg, integument, embryo sac, nucellus, 8. From the statements given below choose the option that are true for a typical female, gametophyte of a flowering plant., [NCERT Exemplar], (i) It is 8-nucleate and 7-celled at maturity, (ii) It is free-nuclear during the development, (iii) It is situated inside the integument but outside the nucellus, (iv) It has an egg apparatus situated at the chalazal end, (a) (i) and (iv), (b) (ii) and (iii), (c) (i) and (ii), (d) (ii) and (iv), 9. Autogamy can occur in a chasmogamous flower if, (a) pollen matures before maturity of ovule, (b) ovules mature before maturity of pollen, (c) both pollen and ovules mature simultaneously, (d) both anther and stigma are of equal lengths., 10. Dioecy states, (a) unisexuality of a flower , (c) bisexuality of a plant , , [NCERT Exemplar], , (b) bisexuality of a flower, (d) unisexuality of a plant, , 11. Choose the correct statement from the following., (a) Cleistogamous flowers always exhibit autogamy, (b) Chasmogamous flowers always exhibit geitonogamy, (c) Cleistogamous flowers exhibit both autogamy and geitonogamy, (d) Chasmogamous flowers never exhibit autogamy, , [NCERT Exemplar], , 12. Which of the following structures are haploid in nature?, (a) nucellus and antipodals , (b) Microspore and antipodals, (c) Egg cell and antipodals , (d) Egg and central cell, , Sexual Reproduction in Flowering Plants 45

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13. Filiform apparatus performs the function of, (a) opening the pollen tube , (c) entry of pollen tube into synergids, , (b) guiding the pollen tube to egg, (d) prevents growth of more than one pollen tube, , 14. Unisexuality of flowers prevent, (a) geitonogamy , (c) xenogamy , , (b) autogamy, (d) both geitonogamy and xenogamy, , 15. A particular species of plant produces light, non-sticky pollen in large numbers and its stigmas, are long and feathery. These modifications facilitate pollination by, [NCERT Exemplar], (a) insects , (b) water, (c) wind , (d) animals., 16. From among the situations given below, choose the one that prevents both autogamy and, geitonogamy. , [NCERT Exemplar], (a) Monoecious plant bearing unisexual flowers, (b) Dioecious plant bearing only male or female flowers, (c) Monoecious plant with bisexual flowers, (d) Dioecious plant with bisexual flowers, 17. In a fertilised embryo sac, the haploid, diploid and triploid structures are [NCERT Exemplar], (a) synergid, zygote and primary endosperm nucleus, (b) synergid, antipodal and polar nuclei, (c) antipodal, synergid and primary endosperm nucleus, (d) synergid, polar nuclei and zygote., 18. In an embryo sac, the cells that degenerate after fertilisation are, [NCERT Exemplar], (a) synergids and primary endosperm cell, (b) synergids and antipodals, (c) antipodals and primary endosperm cell, (d) egg and antipodals., 19. Transfer of pollen grains from the anther to the stigma of another flower of same plant is, called, (a) geitonogamy, (b) autogamy, (c) xenogamy, (d) cross-pollination, 20. While planning for an artificial hybridisation programme involving dioecious plants, which, of the following steps would not be relevant?, [NCERT Exemplar], (a) Bagging of female flower, (b) Dusting of pollen on stigma, , (c) Emasculation , (d) Collection of pollen, 21. In angiosperms, a functional megaspore develops into, (a) embryo sac, (b) endosperm, (c) ovule, , (d) pollen grain, , 22. Scutellum is, (a) grass embryo, , (d) grass cotyledon, , (b) grass seed, , (c) grass fruit, , 23. In the embryos of a typical dicot and a grass, true homologous structures are , , [NCERT Exemplar], (a) coleorhiza and coleoptile, (b) coleoptile and scutellum, (c) cotyledons and scutellum, (d) hypocotyl and radicle., 24. The phenomenon observed in some plants wherein parts of the sexual apparatus is used for, forming embryos without fertilisation is called, [NCERT Exemplar], (a) parthenocarpy , (b) apomixis, (c) vegetative propagation , (d) sexual reproduction., 25. In a flower, if the megaspore mother cell forms megaspores without undergoing meiosis and, if one of the megaspores develops into an embryo sac, its nuclei would be [NCERT Exemplar], (a) haploid , (b) diploid, (c) a few haploid and a few diploid, (d) with varying ploidy., , 46

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26. Function of germ pore is, (a) emergence of radicle , (c) growth of pollen tube , , (b) absorption, (d) release of male gamete, , Answers, 1. (c), 11. (a), 21. (a), , 2. (a), 12. (c), 22. (d), , 3. (d), 13. (b), 23. (c), , 4. (a), 14. (b), 24. (b), , 5. (b), 15. (c), 25. (b), , 6. (a), 16. (b), 26. (c), , 7. (b), 17. (c), , 8. (c), 18. (b), , 9. (c), 19. (a), , 10. (d), 20. (c), , Assertion-Reason Questions, In the following questions a statement of assertion followed by a statement of reason is given. Choose, the correct answer out of the following choices., (a) Assertion and reason both are correct statements and reason is correct explanation for assertion., (b) Assertion and reason both are correct statements but reason is not correct explanation for, assertion., (c) Assertion is correct statement but reason is wrong statement., (d) Assertion is wrong statement but reason is correct statement., 1. Assertion :, Reason :, 2. Assertion, Reason, 3. Assertion, Reason, 4. Assertion, Reason, , :, :, :, :, :, :, , 5. Assertion :, Reason, , :, , 6. Assertion :, Reason :, 7. Assertion :, Reason :, 8. Assertion :, Reason, , :, , 9. Assertion :, Reason, , :, , 10. Assertion :, Reason :, , The endosperm of angiosperms is generally triploid (3n)., It develops from primary endosperm nucleus formed by fusion of haploid male, gamete and diploid secondary nucleus., Dictogamy refers to maturation of male and female sex organs at different times., This is a safeguard against cross fertilisation., Megaspore mother cell undergoes meiosis to produce four megaspores., Megaspore mother cell and megaspores are both haploid., Entomophilous plants produce less pollen when compared to anemophilous plants., The wastage of pollen is reduced to the minimum in entomophilous plants because, of the directional pollination., A structure of a typical microsporangium in angiosperms consists of four wall, layers—epidermis, endothecium, middle layers and tapetum., The function of outer three wall layers is protection and also help in dehiscence of, anther to release pollen., A pollen grains can withstand harsh conditions., The exine of pollen grains is made up of sporopollenin which is resistant to high, temperatures, strong acids or alkali as well as enzymatic degradation., In plants, apomixis is a type of asexual reproduction that mimics sexual reproduction., In apomixis seeds are produced without the fusion of gametes., In coconut, the water represents the free nuclear endosperm and the white kernel, represents the cellular endosperm., PEN undergoes a number of free nuclear divisions which are followed by wall, formation., In monosporic type of embryo development megaspore is situated towards the, micropylar end and remains functional., In monosporic development the embryo sac develops from a single functional, megaspore., Microspore is the first cell of male gametophyte., It is diploid in nature., , Answers, 1. (a), , 2. (c), , 3. (c), , 4. (b), , 5. (b), , 6. (a), , 7. (a), , 8. (c), , 9. (d), , 10. (c), , Sexual Reproduction in Flowering Plants 47

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Case-based/Source-based Question, 1. Study the diagram given below and answer the questions that follow:, , (i), (ii), (iii), Ans. (i), (ii), (iii), , Identify the figure given above., Name the initial cell from which this structure has developed., Draw the next mature stage and label the parts., It is a globular embryo of a dicot plant., Zygote, , 2. Fertilisation is essential for production of seed, but in some angiosperms, seeds develop, without fertilisation., (i) Give an example of an angiosperm that produces seeds without fertilisation., (ii) Name the process., (iii) Explain the two ways by which seeds develop without fertilisation., Ans. (i) In the members of family Asteraceae, seeds develop without fertilisation., (ii) This process is called apomixis., (iii) Two ways by which seeds develop without fertilisation are:, (a) In some species, the diploid (2n) egg cell is formed without reduction division and, develops into embryo without fertilisation., (b) In many varieties of Citrus and mango fruits, some of the nucellar cells surrounding, the embryo sac start dividing, protrude into the embryo sac and then develop into, embryos., 3. Given below is an enlarged view of one microsporangium of a mature anther., , Microspore, mother cells, , 48

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(i) An anther with malfunctioning tapetum often fails to produce viable male gametophytes., Give one reason., (ii) The meiocyte of rice has 24 chromosomes. How many chromosomes are present in its, endosperm?, (iii) State the reason why pollen grains lose their viability when the tapetum in the anther is, malfunctioning., Ans. (i) A malfunctioning tapetum is not able to provide optimum nutrition for the production of, viable male gametophytes., (ii) 36 chromosomes, (iii) Due to malfunctioning of tapetum, the developing pollen grain do not get proper nourishment, and thus lose its viability., 4. Observe the figure of fertilised embryo sac of an angiosperm and answer the questions that follow., , (i) In the embryos of a typical dicot and a grass, which are the true homologous structures?, (ii) Normally one embryo develops in one seed but when an orange seed is squeezed many, embryos of different shapes and sizes are seen. Mention how it has happened., (iii) How many nuclei are present in a fully developed male gametophyte of flowering plants?, Ans. (i) Cotyledons and scutellum, (ii) An orange seed has many embryos because of polyembryony., (iii) Three (one vegetative nucleus and two male nuclei), 5. Observe the diagram of pollen grain with germ tube and two male gametes given below., Answer the questions that follow:, , (i) How many pollen grains and ovules are likely to be formed in the anther and the ovary, of an angiosperm bearing 25 microspore mother cells and 25 megaspore mother cells, respectively?, , Sexual Reproduction in Flowering Plants 49

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(ii) How do the pollen grains of Vallisneria protect themselves?, (iii) If the stamens are well exposed, usually which mode of pollination the plant is expected, to follow?, Ans. (i) 100 pollen grains and 25 ovules, (ii) They have mucilaginous covering to prevent them from getting wet., (iii) Wind-pollination, , Very Short Answer Questions, , [1 mark], , Q. 1. Draw a diagram of a matured microspore of an angiosperm. Label its cellular components, only. , [CBSE (F) 2014], Ans., Generative cell, Vegetative cell, , Q. 2. Give an example of a plant which came into India as a contaminant and is a cause of pollen, allergy. , [CBSE (AI) 2014], Ans. Parthenium or Carrot grass., Q. 3. The microscopic pollen grains of the past are obtained as fossils. Mention the characteristic of, the pollen grains that makes it happen., Ans. The exine of pollen grains have an outermost hard layer composed of a chemical, sporopollenin., It is highly resistant to high temperature, strong acids and alkali. So, pollen grains are obtained, as fossils., Q. 4. State the function of filiform apparatus found in mature embryo sac of an angiosperm. , , [CBSE (F) 2014], Ans. The filiform apparatus guides the pollen tube into the synergid., Q. 5. What is funiculus?, Ans. Funiculus is the stalk of ovule that attaches it to the placenta., Q. 6. How many germ pores are there in the pollen grains of monocots and dicots?, Ans. There are three germ pores in dicots and one in monocots., Q. 7. In maximum angiosperms pollen grains are shed at the two-celled stage. Name the 2 cells., Ans. Vegetative cell and generative cell are the two-celled stage in which pollen grains are shed., Q. 8. Name the component cells of the ‘egg apparatus’ in an embryo sac., [NCERT Exemplar], Ans. Two synergids and an egg., Q. 9. Why do pollen grains of some flowers trigger ‘sneezing’ in some people?, [CBSE (F) 2012], Ans. They result in an allergic reaction., Q. 10. Name the tissue present in the fertilised ovules of angiospermic plants that supplies food and, nourishment to the developing embryo., Ans. Endosperm, Q. 11. How many cells are found in a typical embryo sac?, Ans. There are seven cells in a typical embryo sac. These are one egg cell, two synergids, three antipodal, cells and a central cell., Q. 12. What is an anatropous ovule?, Ans. It is an ovule that is completely inverted through 180° such that the micropyle comes close to the, base of the funiculus and nucellus remains straight., Q. 13. Papaver and Michelia both have multicarpellary ovaries. How do they differ from each, other? , [CBSE (F) 2012], Ans. Papaver has syncarpous gynoecium whereas Michelia has apocarpous gynoecium., , 50

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Q. 14. An anther with malfunctioning tapetum often fails to produce viable male gametophytes., Give any one reason., [CBSE Delhi 2013], Ans. A malfunctioning tapetum does not provide enough nourishment to the developing male, gametophytes and thus fail to produce viable male gametophytes., Q. 15. How is it possible in Oxalis and Viola plants to produce assured seed-sets even in the absence, of pollinators? , [CBSE (F) 2012], Ans. By presence of cleistogamous flowers., Q. 16. A bilobed, dithecous anther has 100 microspore mother cells per microsporangium. How many, male gametophytes this anther can produce?, [CBSE Delhi 2010], Ans. The bilobed anther can produce 1600 male gametophytes., Q. 17. The diploid number of chromosomes in an angiospermic plant is 16. What will be the number, of chromosomes in its endosperm and antipodal cells?, [CBSE 2019 (57/5/1)], Ans. Endosperm—24 chromosomes, Antipodals—8 chromosomes., Q. 18. How do flowers of Vallisneria get pollinated?, [CBSE (F) 2013], Ans. In Vallisneria, the female flower stalk is long to reach the water surface to receive the pollen grains, carried by water currents and then it gets coiled after pollination., Q. 19. How many microspore mother cells would be required to produce one hundred pollen grains, in a pollen sac? And why?, [CBSE (F) 2013], Ans. 1 microspore mother cell undergoes meiosis to form 4 pollen grains. In order to produce 100, pollen grains, 25 microspore mother cells must undergo meiosis., Q. 20. What is pollen–pistil interaction and how is it mediated?, [CBSE (F) 2014], Ans. The ability of the pistil to recognise the pollen followed by its acceptance or rejection is called, pollen–pistil interaction. It is mediated by chemical components of pollen interacting with those, of pistil., Q. 21. How many microsporangia are present in a typical anther of an angiosperm? [CBSE (F) 2013], Ans. Four, Q. 22. Pea flowers produce assured seed sets. Give a reason., [CBSE (AI) 2010], Ans. Pea flowers are cleistogamous, i.e., anther and stigma lie close to each other in closed flowers. So, when anthers dehisce in the flower buds, pollen grains come in contact with the stigma to effect, pollination. Thus, assured seeds are produced in pea., Q. 23. Name the part of the flower which the tassels of the corn-cob represent., [CBSE (AI) 2014], Ans. Style and stigma, Q. 24. Write the function of coleoptile., [CBSE Delhi 2012], Ans. It protects the plumule of the monocot embryo., Q. 25. Write the function of scutellum., [CBSE Delhi 2012], Ans. It provides nourishment and protection to the developing embryo., Q. 26. Name the part of gynoecium that determines the compatible nature of pollen grain. , , [NCERT Exemplar], Ans. Stigma, Q. 27. Who discovered double fertilisation in angiosperms?, Ans. S. G. Nawaschin (1897) discovered double fertilisation in angiosperms., Q. 28. Name a plant in which dichogamy is found., Ans. Magnolia, Q. 29. What is nucellus?, Ans. The body of the ovule consists of a mass of parenchymatous cells rich in reserve food material, which is called nucellus., , Sexual Reproduction in Flowering Plants 51

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Q. 30. Name the common function that cotyledons and nucellus perform., [NCERT Exemplar], Ans. Cotyledons and nucellus provide nourishment., Q. 31. Which are the three cells found in a pollen grain when it is shed at the three-celled stage? , , [NCERT Exemplar], Ans. One vegetative cell and two male gametes., Q. 32. What features of flowers facilitate pollination by birds?, Ans. Presence of a large quantity of nectar, bright colours of petal, fragrance and large flowers attract, birds from long distances., Q. 33. Name the type of pollination in self-incompatible plants., [NCERT Exemplar], Ans. Xenogamy., Q. 34. Mention any two characteristics of pollen grains of plants such as maize and Cannabis., Ans. (i) Pollen grains are small, dry and light in weight, non-sticky., (ii) Pollen are produced in large numbers., Q. 35. Define parthenocarpy., Ans. Parthenocarpy is an economically important process in which seedless fruit is formed without, fertilisation, for example, banana., Q. 36. In a case of polyembryony, if an embryo develops from the synergid and another from the, nucellus, which is haploid and which is diploid?, [NCERT Exemplar], Ans. Synergid embryo is haploid and nucellar embryo is diploid., , Short Answer Questions, , [2 marks], , Q. 1. In the T.S. of a mature anther given below, identify “a” and “b” and mention their function.,    , , Ans. a—Sporogenous tissue: It forms pollen grains., , b—Tapetum: It provides nourishment to the developing pollen grains., Q. 2. In a flowering plant a microspore mother cell produce four male gametophytes while a, megaspore mother cell form only one female gametophyte. Explain., [CBSE Delhi 2017], Ans. Male gametophytes are formed by meiosis of single microspore mother cell whereas female, gametophytes are formed by meiosis of single megaspore mother cell to produce 4 megaspores,, out of which 3 degenerate and only one survives. The surviving megaspore undergoes mitotic, division to form the female gametophyte., Q. 3. Name the organic materials the exine and intine of an angiosperm pollen grains are made up, of. Explain the role of exine., [CBSE Delhi 2014], Ans. Exine is made up of sporopollenin and intine is made up of cellulose and pectin. Exine is the most, resistant organic material and can withstand high temperature, acidic and alkali environment., Q. 4. Differentiate between the two cells enclosed in a mature male gametophyte of an, angiosperm. , [CBSE (AI) 2013], Ans., Table 2.7: Differences between vegetative and generative cell of pollen grain, S.No., , 52, , Vegetative cell, , Generative cell, , (i), , It is bigger in size., , It is smaller and floats in the cytoplasm of vegetative cell., , (ii), , It has food reserves., , It gives rise to two male gametes.

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Q. 5. “Pollen grains in wheat are shed at 3-celled stage while in peas they are shed at 2-celled stage.”, Explain. Where are germ pores present in a pollen grain?, [CBSE (AI) 2017], Ans. At the time of shedding wheat pollen consists of one vegetative and two male gametes, which is, the 3-celled stage. While pea pollen consists of one vegetative and one generative cell which is the, 2-celled stage. Germ pores are present on the exine where sporpollenin is absent., Q. 6. Gynoecium of a flower may be apocarpous or syncarpous. Explain with the help of an example, each. , [CBSE (AI) 2016], Ans. The gynoecium represents the female reproductive part of the flower. When there are more than, one pistil, if the pistils are fused together, the flower is said to be syncarpous and if the pistils are, free, it is said to be apocarpous. For example, pistil of Papaver is syncarpous and that of Michelia, is apocarpous., Q. 7. Name all the haploid cells present in an unfertilised mature embryo sac of a flowering plant., Write the total number of cells in it., [CBSE (AI) 2013], Ans. The haploid cells in an unfertilised mature embryo sac are: egg cell, synergids, antipodals and, central cell. There are 7 cells in total., Q. 8. Draw a diagram of pollen grain with germ tube and two male gametes., Ans., , Q. 9. Why does the zygote begin to divide only after the division of primary endosperm cell? , , [NCERT Exemplar], Ans. The zygote needs nourishment during its development. As the mature, fertilised embryo sac, offers very little nourishment to the zygote, the primary endosperm cell (PEC) divides and, generates the endosperm tissue which nourishes the zygote. Hence, the zygote always divides, after division of PEC., a, Q. 10. Given alongside is an enlarged view of one microsporangium, of a mature anther., b, , (i) Name ‘a’, ‘b’ and ‘c’ wall layers. , , (ii) Mention the characteristics and function of the cells, Microspore, forming wall layer ‘c’.      , mother cells, Ans. (i) a = Endothecium, b = Middle layers, c = Tapetum, c, (ii) Tapetum provides nourishment to the developing pollen, grains. The tapetal cells also secrete Ubisch granules that, provide sporopollenin and other materials for exine formation., Q. 11. Which is the triploid tissue in a fertilised ovule? How is the triploid condition achieved? , , [NCERT Exemplar], Ans. The triploid tissue in the ovule is the endosperm. Its triploid condition is achieved by the fusion, of two polar nuclei and one nucleus of male gamete, referred to as triple fusion., Q. 12. Fill in the following labels with the type of cell function., X, , A, , B, , Ans. X—Meiosis (Reduction division); A—Mitosis;, polar nuclei, antipodals and egg apparatus., , C, , D, , B—Mitosis; C—Mitosis; D—Cells reorganised as, , Sexual Reproduction in Flowering Plants 53

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Q. 13. Mention the ploidy of the different types of cells present in the female gametophyte of an, angiosperm. , [CBSE Delhi 2017], Ans. , Table 2.8: Ploidy of cells in female gametophyte, Cells in female gametophyte, , Their ploidy, , 1. Synergids, , Haploid, , 2. Egg, , Haploid, , 3. Polar nuclei, , Haploid, , 4. Antipodals, , Haploid, , 5. Central cell, , 2 haploid nuclei, , Q. 14. Write briefly the role of pollination in the growth and development in an angiosperm., Ans. Pollination is transfer of pollen grains from anthers to the stigma of a flower. Pollination is, prerequisite for fertilisation, events after fertilisation like endosperm development, seed setting, and fruit formation. Thus, pollination plays an important role in the growth and development of, angiosperms., Q. 15. Explain any two devices by which autogamy is prevented in flowering plants., Ans. (i) Male and female flowers are present on different plants., (ii) The stamens and stigma of a bisexual flower mature at different times., (a) Anthers mature earlier than the stigma and release pollens., (b) The stigma matures earlier than the anther., (iii) Flowers are self-sterile or self-incompatible., (iv) Chasmogamous flowers are present with exposed stamens and stigma which facilitate crosspollination. , (Any two), Q. 16. What is cleistogamy? Write one advantage and one disadvantage of it, to the plant. , , [CBSE 2019 (57/4/1)], Ans. Pollination occurring in closed flowers is referred to as cleistogamy., , Advantage: It ensures self-pollination and assured seed set formation in absence of pollinators., Disadvantage: It does not allow cross-pollination. This can cause inbreeding depression as there, will be no genetic variation., Q. 17., , (a) List any two characteristic features of wheat flowers that make it a good example of wind, pollination., , (b) It is observed that plant breeders carrying out wheat hybridisation often take pollen grains, from the ‘pollen banks’. Do you agree ? Give one reason in support of your answer. , , [CBSE 2019 (57/3/1)], Ans. (a) Light pollen grains/Pollen grains more in number/well exposed stamen/feathery and sticky, stigma/Numerous flowers are packed into an inflorescence., (Any two), (b) Yes., Viability of wheat pollen grain is only 30 minutes and so it is stored in pollen bank for a long, period of time for later use., Q. 18. List the two steps that are essential for carrying out artificial hybridisation in crop plants and, why. , [CBSE (F) 2014], Ans. (a) Selection of parents: Only those plants should be selected which have desired traits., , Emasculation: Removal of anthers from flower before they are mature and dehisce., (b) Crossing over: Pollen grains from selected male plant is collected and transferred to the, female plant after which it is bagged., Q. 19. Explain the steps that ensure cross pollination in an autogamous flower., [CBSE Delhi 2013], Ans. A bisexual flower is emasculated at unopened stage to prevent self-pollination in the flower and, it is bagged after emasculation to prevent contact of unwanted pollen grain with the stigma of, , 54

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the flower. Artificial pollination is then performed when the stigma is ready and the flower is, rebagged., Q. 20. Geitonogamous flowering plants are genetically autogamous but functionally cross-pollinated., Justify. Give similarity of geitonogamy with autogamy and xenogamy., [CBSE Delhi 2013], Ans. Geitonogamous flowers are genetically autogamous because both male and female flowers are, borne on the same plant. They are functionally cross-pollinated because the pollen from one, flower is transferred to the stigma of a different flower., Q. 21. How does the Mediterranean orchid Ophrys ensures its pollination by bees? [CBSE Delhi 2010], Ans. The petals of the Ophrys resemble the female of a bee species in size, colour and odour. Male bee, mistakes the Ophrys for female bee and tries to copulate. Few pollen grains adhered to the body of, the male bee fall over stigma of the flower thereby leading to pollination showing sexual deceit., Q. 22. Why should a bisexual flower be emasculated and bagged prior to artificial pollination?, , [CBSE (F) 2010], Ans. A bisexual flower is emasculated to prevent self-pollination in the flower and it is bagged after, emasculation to prevent contact of unwanted pollen grain with the stigma of the flower., Q. 23. Write the cellular contents carried by the pollen tube. How does the pollen tube gain its entry, into the embryo sac?, [CBSE (F) 2012], Ans. Pollen tube carries two male gametes., Pollen tube, after reaching the ovary, enters the ovule through the micropyle and then enters one, of the synergids through the filiform apparatus which guides the entry of pollen tube into egg, cell., Q. 24. A pollen grain in angiosperm at the time of dehiscence from an anther could be 2-celled or, 3-celled. Explain. How are the cells placed within the pollen grain when shed at a 2-celled, stage? , [CBSE (AI) 2017], Ans. In 2-celled stage the mature pollen grain contains one generative and vegetative cells, whereas in, 3-celled stage one vegetative cell and two male gamete cells are present., The generative cell being small floats in the cytoplasm of the vegetative cell. The pollen grains are, shed at this 2-celled stage., Q. 25. State one advantage and one disadvantage of cleistogamy., [CBSE (AI) 2012], Ans. Advantage: Self-pollination is assured/Seed production is assured., Disadvantage: Least variations observed/Leads to inbreeding depression., Q. 26. Name the product of fertilisation that forms the kernel of coconut. How does the kernel differ, from coconut water?, [CBSE (F) 2012], Ans. Endosperm forms the kernel of coconut., The coconut water is free-nuclear endosperm whereas kernel is cellular endosperm., Q. 27. List the post-fertilisation events in angiosperms., [CBSE Delhi 2014], Ans. (i) Development of endosperm, (ii) Embryogeny/development of embryo, (iii) Seed formation, (iv) Fruit formation, Q. 28. Mention the function of each of the following:, (a) Tassels of corn cob., (b) Tapetum in the microsporangium. , [CBSE (F) 2012], Ans. (a) These are the stigma and style which wave in the wind to trap pollen grains., (b) Provides nourishment to the developing pollen grains., Q. 29. Describe the development of endosperm after double fertilization in an angiosperm. Why, does endosperm development proceeds that of zygote?, [CBSE Delhi 2015], Ans. Refer to Basic Concepts Point 9 (Endosperm Development)., Cells of the endosperm provide nutrition to the developimh embryo., , Sexual Reproduction in Flowering Plants 55

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Q. 30. Draw a vertical section of a maize grain and label (i) pericarp, (ii) scutellum, (iii) coleoptile and, (iv) radicle. , [CBSE 2019 (57/5/1)], Ans. Refer to Fig. 2.15(d)., Q. 31. Explain the function of each of the following:, (a) Coleorhiza     , (b) Germ pores , [CBSE (AI) 2012], Ans. (a) Coleorhiza protects the radical of (monocot) embryo., (b) Germ pores allow germination of pollen grain and formation of pollen tubes., Q. 32. Differentiate between albuminous and non-albuminous seeds, giving one example of each. , , [CBSE Delhi 2011], Ans. Albuminous seeds have residual endosperm in them. For example, maize., Non-albuminous seeds do not have any residual endosperm. For example, pea., Q. 33. Mention the reasons for difference in ploidy of zygote and primary endosperm nucleus in an, angiosperm. , [CBSE Delhi 2010], OR, In angiosperms, zygote is diploid while primary endosperm cell is triploid. Explain., , [CBSE (AI) 2013], Ans. A zygote is formed by the fusion of haploid male gamete with the haploid egg to form a diploid, cell; whereas, primary endosperm nucleus (PEN) is formed by the fusion of haploid male gamete, with two haploid polar nuclei, forming a triploid nucleus., Q. 34. Some angiosperm seeds are said to be ‘albuminous’, whereas few others are said to have a, perisperm. Explain each with the help of an example., [CBSE (F) 2014], Ans. Albuminous seeds are those which retain a part of endosperm as it is not completely used up, during embryo development. For example, in wheat and maize. In some seeds remnants of, nucellus are also persistent. This residual, persistent nucleus is the perisperm. For example, in, black pepper and beet., Q. 35. Double fertilisation is reported in plants of both, castor and groundnut. However, the, mature seeds of groundnut are non-albuminous and castor are albuminous. Explain the postfertilisation events that are responsible for it., [CBSE Delhi 2015], Ans. The development of endosperm (preceding the embryo) takes place from primary endosperm, nucleus (PEN) in both, castor and groundnut., The developing embryo derives nutrition from endosperm., PEN undergoes repeated division to give free nuclei. Subsequently cell wall is formed and, endosperm becomes cellular. At this stage endosperm is retained in castor or is not fully consumed, but in groundnut endosperm is consumed by growing embryo., Q. 36., , (a) You are given castor and bean seeds. Which one of the two would you select to observe the, endosperm?, , (b) The development of endosperm precedes that of embryo in plants. Justify. , , [CBSE 2019 (57/2/1)], Ans. (a) Castor, (b) Endosperm stores reserve food materials. It provides nutrition to the developing embryo,, therefore its development precedes that of embryo., Q. 37., , (a) Mature seeds of legumes are non-albuminous. Then, can it be assumed that double, fertilisation does not occur in legumes? Explain your answer., , (b) List the differences between the embryos of dicot (pea) and monocot (grass family)., , [CBSE (AI) 2014], Ans. (a) No it cannot be assumed so because fertilisation does takes place but the endosperm is, consumed during embryo development., , 56

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(b), , Table 2.9: Differences between dicot and monocot embryo, S. No., , Dicot embryo, , Monocot embryo, , (i), , It has two cotyledons., , It has one cotyledon., , (ii), , Radicle and plumule are not covered with, sheath., , Radicle is covered with coleorhiza and, plumule is covered by coleoptile., , Q. 38. Draw a sectional view of an apple and label the different parts of an ovary in it. Fruits develop, from an ovary. Then why is apple referred to as a false fruit?, [CBSE (F) 2013, 2017], Ans. Refer to Fig. 2.16(a)., In apple, the thalamus also contributes to fruit formation. Therefore, it is called a false fruit., Q. 39. What is pericarp? Mention its functions., Ans. The wall of the ovary that develops into wall of the fruit is called pericarp., , Functions: (i) Protects the seed till its maturity.,   (ii) Helps in seed dispersal., Q. 40. A non-biology person is quite shocked to know that apple is a false fruit, mango is a true fruit, and banana is a seedless fruit. As a biology student how would you satisfy this person? , , [CBSE Delhi 2015], Ans. In apple only the thalamus (along with ovary) portion contributes to fruit formation. Therefore,, it is a false fruit. Mango develops only from the ovary, therefore it is a true fruit., Banana develops from ovary but without fertilisation. The method is known as parthenocarpy., Since there is no fertilisation, no seeds are formed in banana., Q. 41. Why are some seeds referred to as apomictic seeds? Mention one advantage and one, disadvantage to a farmer who uses them., [CBSE (AI) 2015; (F) 2015], Ans. Seeds that are produced without fertilisation are referred to as apomictic., , Advantage: Desired characters are retained in offspring (progeny) as there is no segregation of, characters in offspring (progeny). Seed production is assured even in absence of pollinators., Apomictic seeds are economical as they can be used to grow crops year after year., , Disadvantage: Cannot control accumulation of deleterious genetic mutation. These are usually, restricted to narrow ecological niches and lack ability to adapt to changing environment., Q. 42. Explain any two ways by which apomictic seeds get developed., [CBSE (F) 2013], Ans. Ways by which apomictic seeds develop are:, (i) A diploid egg is formed without reduction division which develops into embryo without, fertilisation., (ii) Some cells of the nucellus, which are diploid in nature, start dividing and without fertilisation, develop into embryo., Q. 43. If you squeeze a seed of orange you might observe many embryos of different sizes? How is it, possible? Explain. , [CBSE (AI) 2010, Delhi 2011], Ans. In orange, the nucellar cells surrounding the embryo sac start dividing, protrude into the embryo, sac and develop into a number of embryos of different sizes., Q. 44. Banana is a parthenocarpic fruit whereas oranges show polyembryony. How are they different, from each other with respect to seeds?, Ans. Banana develops from an ovary without fertilisation having non-viable seeds so it is called, parthenocarpic fruit. An orange contain seeds with more than one embryo thus, it shows, polyembryony., Q. 45., , (a) How are parthenocarpic fruits produced by some plants and apomictic seeds by some, others? Explain., , (b) When do farmers prefer using apomictic seeds?, [CBSE (AI) 2016], Ans. (a) Parthenocarpic fruits are formed when ovary develops into fruit without fertilisation., Apomictic seeds are formed when formation of seeds take place without fertilisation., , Sexual Reproduction in Flowering Plants 57

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(b) To maintain hybrid characters (year after year in a desired plant) and to avoid buying hybrid, seeds every year (expensive seeds) farmers prefer using apomictic seeds., Q. 46. What is agamospermy? How is agamospermy different from parthenogenesis and parthenocarpy?, Ans. The phenomenon of asexual reproduction that mimics sexual reproduction as it forms seed, without fertilisation is called agamospermy., Parthenogenesis refers to the development of unfertilised egg into an adult individual. On the, other hand, parthenocarpy is the phenomenon of formation of fruits without fertilisation of an, ovary., , Long Answer Questions–I, , [3 marks], , Q. 1., , (a) Name the organic material exine of the pollen grain is made up of. How is this material, advantageous to pollen grain?, (b) Still it is observed that it does not form a continuous layer around the pollen grain. Give, reason., (c) How are ‘pollen banks’ useful?, [CBSE (AI) 2016], Ans. (a) Sporopollenin, It is most resistant material to high temperature, strong acids on alkali and no enzymes can, degrade it., (b) Germs pores are present to allow pollen tube to emerge out for pollen germination., (c) Pollen banks help in storing pollen grains for years for crop breeding programmes., Q. 2. Write the functions of:, (a) Coleoptile , (b) Tapetum   , (c) Scutellum [CBSE Delhi 2012], Ans. (a) Coleoptile: It protects the plumule of the monocot embryo., (b) Tapetum: It provides nourishment to developing pollen., (c) Scutellum: It provides nourishment and protection to the developing embryo., Q. 3. When and where do tapetum and synergids develop in flowering plants? Mention their, functions. , [CBSE 2019 (57/2/1)], Ans. Tapetum develop during microsporogenesis in the microsporangium (anther). It nourishes the, developing pollen grains., Synergids develop during megasporogenesis in the megasporangium (ovule). Synergids have, filiform apparatus to guide the pollen tube into it., Q. 4. Where are the following structures present in a male gametophyte of an angiosperm? Mention, the function of each one of them., (a) Germ pore   (b) Sporopollenin, (c) Generative cell, [CBSE 2019 (57/2/1)], Ans. (a) Germ pore: Exine of pollen grain. It is the site from where pollen tube emerges., (b) Sporopollenin: Exine of pollen grains. It protects the pollen grains from high temperature,, strong acids and alkali, enzymes and adverse conditions., (c) Generative Cells: These are present in pollen grains. These give rise to two male gametes., Q. 5. Draw the diagram of microsporangium of an angiosperm and label any four parts. State the, function of its innermost wall layer., [CBSE Sample Paper 2015, 2017, 2018], Ans. Refer to Fig. 2.3(b)., Tapetum nourishes the developing pollen grains, Q. 6. Make a list of any three outbreeding devices that flowering plants have developed and explain, how they help to encourage cross-pollination., [CBSE (AI) 2014], Ans. (i) Time of pollen release and stigma receptivity are different (not synchronised). This prevents, self-pollination., (ii) Anther and stigma are placed at different positions, so the pollens cannot come in contact, with the stigma of the same flower., , 58

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(iii) Self-incompatibility, which is a genetic mechanism to prevent the pollen germination on the, stigma of the same flower., Q. 7. Why are angiosperm anthers called dithecous? Describe the structure of its microsporangium., , [CBSE (AI) 2014], Ans. The anthers of angiosperms are called dithecous because they are bilobed and each lobe of anther, has two theca., Microsporangium is surrounded by four wall layers named as epidermis, endothecium, middle, layer and tapetum. In young anther, a group of compactly arranged homogenous cells called, sporogenous tissue occupies the centre of each microsporangium which produce microspores or, pollen grains., Q. 8. The generative cell of a 2-celled pollen divides in the pollen tube but not in a 3-celled pollen., Give reasons. , [NCERT Exemplar] [HOTS], Ans. In a 3-celled pollen, the generative cell has already divided and formed 2 male gametes. Hence, it, will not divide again in the pollen tube. As the generative cell has not divided in a 2-celled pollen,, it divides in the pollen tube., Q. 9. During an excavation assignment, scientists collected pollen grains of a plant preserved in, deeper layers of soil. Analyse the properties of pollen grains which help in the fossilization. , , [CBSE Sample Paper 2016] [HOTS], Ans. Pollen has an outer layer called exine which is made of sporopollenin., It is the most resistant organic material known. It can withstand high temperature, strong acids, and alkali as well. No enzyme that degrades sporopollenin is so far known., Q. 10. Draw a longitudinal section of a post-pollinated pistil showing entry of pollen tube into a, mature embryo sac. Label filiform apparatus, chalazal end, hilum, antipodals, male gametes, and secondary nucleus., [CBSE Delhi 2010; 2019 (57/4/1)], Ans. Refer to Fig. 2.12(a) and (b)., Q. 11. (a) Draw a labelled sketch of a mature 7-celled, 8-nucleate embryo-sac., (b) Which one of the cell in an embryo-sac produce endosperm after double fertilisation? , , [CBSE (F) 2016], Ans. (a) Refer to Fig. 2.8(c), (b) Central cell, Q. 12. What will be the ploidy of the cells of the nucellus, microspore mother cell, the functional, megaspore and female gametophyte?, [HOTS], Ans. Nucellus, : Diploid, Microspore mother cell, : Diploid, The functional megaspore : Haploid, Female gametophyte, : Haploid, Q. 13. Given below are the events that are observed in artificial hybridisation programme. Arrange them, in the correct sequential order in which they are followed in the hybridisation programme., (a) re-bagging; , (b) selection of parents;, (c) bagging; , (d) dusting the pollen on stigma;, (e) emasculation; , (f) collection of pollen from male parent. , , [NCERT Exemplar] [HOTS], Ans. (b); (e); (c); (f); (d); (a)., Q. 14. Explain the process of artificial hybridisation to get improved crop variety in (i) plants bearing, [CBSE (AI) 2010], bisexual flowers (ii) female parent producing unisexual flowers., Ans. (i) In plants bearing bisexual flowers, the anthers are removed from the flower before they, dehisce. This is called emasculation. The emasculated flowers are covered with a bag of, butter paper to prevent contamination of stigma with unwanted pollen. This process is called, bagging. When this stigma attains receptivity, mature pollen grains are dusted on the stigma, and the flowers are rebagged to allow the fruits to develop., , Sexual Reproduction in Flowering Plants 59

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(ii) If the female parent produces unisexual flowers, emasculation is not done. The flower buds, are bagged before the flowers open. When the stigma becomes receptive, pollen is dusted on, stigma and the flower is rebagged., Q. 15. Differentiate between geitonogamy and xenogamy in plants. Which one between the two will, lead to inbreeding depression and why?, [CBSE Delhi 2011], Ans., Table 2.10: Differences between geitonogamy and xenogamy, S. No., , Geitonogamy, , Xenogamy, , (i), , It is transfer of pollen grains from the anther, to the stigma of another flower of same plant., , It is transfer of pollen grains from the anther, to the stigma of a different plant., , (ii), , The pollen grains are genetically similar to the, plant., , The pollen grains are genetically different, from the plant., , Geitonogamy will lead to inbreeding depression because the pollen grains are genetically similar,, which results in inbreeding. Continued inbreeding will thus reduce fertility and productivity., Q. 16. Write the differences between wind-pollinated and insect-pollinated flowers. Give an example, of each type. , [CBSE (F) 2014], Ans., Table 2.11: Differences between wind-pollinated and insect-pollinated flowers, S. No., , Wind-pollinated flowers, , Insect-pollinated flowers, , (i), , These produce large numbers of pollen grains., , These produce less number of pollen grains., , (ii), , These are dull, nectarless and scentless., , These are bright, scented and have nectar., , (iii), , Stamens are long and protrude above petals., , Stamens lie within the corolla tube., , (iv), , The pollen grains are dry, light, small and, smooth., For example, ragweed., , The pollen grains are larger, heavier with, appendages like hooks and barbs., For example, rose, sweet pea., , Q. 17. (i) Write the characteristic features of anther, pollen and stigma of wind-pollinated flowers., (ii) How do flowers reward their insect pollinators? Explain., [CBSE (AI) 2010, 2012], Ans. (i) The characteristics of wind-pollinated flowers are:, (a) Pollen grains are light in weight, non-sticky, dry and winged, so that they can be easily, transported., (b) Well-exposed stamens for easy dispersal of pollen grains in the wind., (c) The stigma is sticky, large, feathery to trap pollen grains in air., (d) Numerous flower are packed together to form inflorescence., (d) The flowers are small and inconspicuous., (ii) Insect pollinators are rewarded in following ways:, (a) The flowers offer floral reward like nectar and pollen grain., (b) In some species floral reward provides safe place to lay eggs., Q. 18. (a), (b), Ans. (a), (b), , Mention any four strategies adopted by flowering plants to prevent self-pollination., Why is geitonogamy also referred to as genetical autogamy?, [CBSE (AI) 2010], Refer to Basic Concepts Point 5 [Contrivances for self-pollination (Autogamy)]., Geitonogamy is the transfer of pollen grains from the anther to the stigma of another flower, of the same plant. Although geitonogamy is functionally cross-pollination involving a, pollinating agent, genetically it is similar to autogamy, since the pollen grains come from the, same plant., , Q. 19. State the significance of pollination. List any four differences between wind-pollinated and, animal pollinated flowers., Ans. Pollination is the phenomena of transfer of pollen grains from anthers to the stigma of a pistil., Pollination is prerequisite for the beginning of fertilisation., , 60

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Table 2.12: Differences between wind-pollinated and animal-pollinated flowers, S. No., , Wind-pollinated flowers, , Animal-pollinated flowers, , (i), , This kind of flower is pollinated by abiotic This kind of flower is pollinated by biotic, pollinating agent., pollinating agent., , (ii), , They are small and inconspicuous., , (iii), , The pollen grains are dry, light and non-sticky The pollen gains are generally sticky in animal, so that they can be easily transported by wind. pollinated flowers., , (iv), , The flowers are often clustered so as to carry Flowers reward pollinators in terms of pollen,, out pollination., nectar or safe place to lay eggs., , They are large, colourful, fragrant and rich in nectar., , Q. 20. (a) How does cleistogamy ensure autogamy?, (b) State one advantage and one disadvantage of cleistogamy to the plant. , , [CBSE (AI) 2012; Delhi 2013], Ans. (a) Cleistogamous flowers do not open. Therefore, the pollens have to land on the stigma of the, same flower. This ensures autogamy., (b) Advantage: Self-pollination is assured, thus ensuring seed formation., Disadvantage: Least variations observed and it leads to inbreeding depression., Q. 21. (a) Describe the endosperm development in coconut., (b) Why is tender coconut considered a healthy source of nutrition?, (c) How are pea seeds different from castor seeds with respect to endosperm? , , [CBSE (AI) 2013], Ans. (a) The primary endosperm nucleus (PEN) undergoes successive nuclear divisions to give rise to, free nuclei. Subsequently, cell wall is formed towards the periphery and endosperm becomes, cellular, leaving free nuclear endosperm in the central part. This division is followed by, cytokinesis and thus endosperm becomes cellular and is called cellular endosperm., (b) It is rich in many nutrients like fats, proteins, carbohydrates, minerals, vitamins. Hence,, tender coconut is considered a healthy source of nutrition., (c) In peas, the endosperm is used up and there is no endosperm present in the mature seed. In, castor, the endosperm remains intact in the mature seed., Q. 22. Differentiate between perisperm and endosperm by giving one example of each. , , [CBSE (AI) 2012], Ans., Table 2.13: Differences between perisperm and endosperm, S. No., , Perisperm, , Endosperm, , (i), , It is persistent nucellus., , It is the nutritive tissue for embryo., , (ii), , It is diploid., , It is triploid., , (iii), , Example: black pepper, beet., , Example: maize, rice, wheat, castor., , Q. 23. Explain any three advantages the seeds offer to angiosperms., [CBSE Delhi 2014], Ans. (i) Since reproductive process such as pollination and fertilisation are independent of water,, seed formation is more dependable., (ii) Seeds have better adaptive strategies for dispersal to new habitats and help the species to, colonise in other areas., (iii) As they have sufficient food reserves young seedlings are nourished until they are capable of, photosynthesis on their own., (iv) The hard seed coat provides protection to the young embryo., (v) Being products of sexual reproduction, they generate new genetic combinations or, variations. , (Any three), , Sexual Reproduction in Flowering Plants 61

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Q. 24. State what is apomixis. Comment on its significance. How can it be commercially used?, , Ans. Refer to NCERT Textbook Exercise, Q. No. 18., , [CBSE (AI) 2015; 2019 (57/4/1)], , Q. 25. Differentiate between parthenocarpy and parthenogenesis. Give one example of each. , , [CBSE 2018], Ans., Table 2.14: Differences between parthenocarpy and parthenogenesis, S. No., , Parthenocarpy, , Parthenogenesis, , (i), , It is process of formation of fruit without, fertilisation, , It is the process of development of new, organism without fertilisation., , (ii), , For example, banana, grapes, etc., , For example, drones, male honey bee, turkey,, rotifers, etc., , Q. 26., , (a) How are parthenocarpic fruits produced by some plants and apomictic seeds by some, others? Explain., (b) When do farmers prefer using apomictic seeds?, [CBSE (AI) 2016], Ans. (a) Parthenocarpic fruits are formed when ovary develops into fruit without fertilisation., Apomictic seeds are formed when formation of seeds take place without fertilisation., (b) To maintain hybrid characters (year after year in a desired plant) and to avoid buying hybrid, seeds every year (expensive seeds) farmers prefer using apomictic seeds., Q. 27. (a) How does a farmer use the dormancy of seeds to his advantage?, (b) What advantages a seed provides to a plant?, [CBSE (AI) 2016], Ans. (a) Dormancy of mature seeds are important for storage of seeds which can be used as food, throughout the year and also to raise crop in the next season., (b) Seeds offer several advantages to angiosperms. Firstly, since reproductive processes such as, pollination and fertilisation are independent of water, seed formation is more dependable., Also seeds have better adaptive strategies for dispersal to new habitats and help the species to, colonise in other areas. As they have sufficient food reserves, young seedlings are nourished, until they are capable of photosynthesis on their own. The hard seed coat provides protection, to the young embryo. Being products of sexual reproduction, they generate new genetic, combinations leading to variations., Q. 28. Draw a diagram of L.S. of an anatropous ovule of an angiosperm and label the following parts., (i) Nucellus , (ii) Integument, (iii) Antipodal cells, (iv) Secondary nucleus, Ans. Refer to Fig. 2.7., Q. 29. ‘Fertilisation is not an obligatory event for fruit production in certain plants’. Explain the, statement. , [HOTS], Ans. This can be observed in parthenocarpic fruits. The ‘seedless fruits’ that are available in the market,, such as pomegranate, grapes, etc., are good examples. Flowers of these plants are sprayed by a, growth hormone that induces fruit development even though fertilisation has not occurred. The, ovules of such fruits, however, fail to develop into seeds., Q. 30. Is pollination and fertilisation necessary in apomixis? Give reasons. [NCERT Exemplar] [HOTS], Ans. No, they are not necessary. Apomixis is actually an alternative to sexual reproduction, although the, female sexual apparatus is used in the process. In apomicts, embryos can develop directly from the, nucellus or synergid or egg. Therefore, there is no need for either pollination or fertilisation., Q. 31. Embryo sacs of some apomictic species appear normal but contain diploid cells. Suggest a, suitable explanation for the condition., [NCERT Exemplar] [HOTS], Ans. Many apomictic species have been seen to have normal looking embryo sacs. The only possibility, of the embryo sac possessing diploid cells will be due to failure of meiotic division at the megaspore, mother cell stage. Since the megaspore mother cell has a diploid nucleus, if it undergoes mitosis, instead of meiosis, all the resulting nuclei and cells will be diploid in nature., , 62

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Long Answer Questions–II, , [5 marks], , Q. 1. Draw a labelled diagram of an anther lobe at microspore mother cell stage. Mention the role, of different wall layers of anther., Ans. Refer to Fig. 2.3., Roles of different wall layers of anther:, (i) Epidermis, endothecium and middle layers perform the function of protection and help in, dehiscence of anther to release the pollen., (ii) Tapetum is the innermost wall layer and it provides nourishment to the developing pollen, grains., Q. 2., , (a) Draw a diagram of an enlarged view of T.S. of one microsporangium of an angiosperm, and label the following parts:, (i) Tapetum, (ii) Middle layer, (iii) Endothecium, (iv) Microspore mother cells, (b) Mention the characteristic features and function of tapetum., (c) Explain the following giving reasons:, (i) Pollen grains are well preserved as fossils., (ii) Pollen tablets are in use by people these days., [CBSE (F) 2011], Ans. (a) Refer to Fig. 2.3(b)., (b) Tapetum is the innermost wall layer of the microsporangium. It nourishes the developing, pollen grains. Cells of the tapetum possess dense cytoplasm and generally have more than, one nucleus., (c) (i) Pollen grains have thick outer exine which is composed of sporopollenin., Sporopollenin can withstand high temperatures and strong acids and alkalis and are, not degraded by any enzymes. Therefore, they are well preserved as fossils., (ii) Pollen tablets are used by people because pollens are rich in nutrients so used to increase, performance of athletes and race horses., Q. 3. Draw a labelled diagram of the sectional view of a mature pollen grain in angiosperms., Explain the functions of its different parts., Ans., , Functions:, (i) Pollen grains are generally spherical with a prominent two-layered wall. The hard outer, layer is called exine made up of sporopollenin, which is a resistant organic material., (ii) Exine can withstand high temperature, strong acids and alkali, thus provide protection., (iii) It has prominent aperture called germ pore, through which pollen tube comes out., (iv) Vegetative cell has abundant food reserve., (v) Generative cell divides mitotically giving rise to two male gametes, before pollen grains are, shed (3-celled stage)., , Sexual Reproduction in Flowering Plants 63

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Q. 4., , (a) Where is microsporangium located in an angiosperm ? State the functions of tapetum and, the other three layers of microsporangium?, (b) Describe the structure of the male gametophyte produced as a result of microsporogenesis., (c) State the functions of each part of the male gametophyte., [CBSE 2019 (57/3/3)], Ans. (a) Microsporangium is located in the anther lobe., Tapetum nourishes the developing pollen grain., The other three layers of microsporangium, i.e., epidermis, endothecium and middle layers, protect and dehisce the microsporangium., (b) Structure of Pollen grain/male gemetophyte., (i) Outer wall layer of the male gametophyte is called exine. It is a hard layer, made of, sporopollenin. It protects the pollen grain., (ii) Inner wall layer is called as intine. It is made up of cellulose and pectin., (iii) Vegetative cell is rich in food reserve. It helps in formation of pollen tube., (iv) Generative cell is smaller and has dense cytoplasm and a nucleus. It forms the two male, gametes., Q. 5. Describe in sequence the events that lead to the development of a 3-celled pollen grain from, microspore mother cell in angiosperms., [CBSE (AI) 2010], Ans. Refer to Basic Concept Point 3 (Microsporogenesis and Pollen grains)., Q. 6. (a) How does microspore mother cell develop into mature pollen grain in angiosperms?, (b) Describe the structure of a mature pollen grain and draw a labelled diagram of its twocelled stage., [CBSE (F) 2012], Ans. (a) Refer to Basic Concepts Point 3 (Microsporogenesis)., (b) Refer to Basic Concepts Point 3 (Pollen grains). For diagram refer to Fig. 2.5 (b), Q. 7. Draw a diagrammatic sectional view of a mature anatropous ovule and label the following, parts in it:, (a) that develops into an endosperm in an albuminous seed., (b) through which the pollen tube gains entry into the embryo sac., (c) that attaches the ovule to the placenta., Ans. Refer to Fig. 2.7., Q. 8., , (a) Draw a diagram of a mature embryo sac of an angiosperm and label the following parts in, it:, (i) Filiform apparatus, (ii) Synergids, (iii) Central cell, (iv) Egg cell, (v) Polar nuclei, (vi) Antipodals, (b) Write the fate of egg cell and polar nuclei after fertilisation., [CBSE Delhi 2013], Ans. (a) Refer to Fig. 2.8 (c)., (b) After fertilisation egg cell fuses with male gamete to form zygote and polar nuclei fuse with, other male gamete to form primary endosperm nucleus., Q. 9., , (a) Trace the development of megaspore mother cell up to the formation of a mature embryo, sac in a flowering plant., (b) Draw a labelled diagram of the structure of mature dicot embryo. , , [CBSE (AI) 2010; 2019 (57/4/1)], OR, How does the megaspore mother cell develop into 7-celled, 8 nucleate embryo sac in an, angiosperm? Draw a labelled diagram of a mature embryo sac., [CBSE Delhi 2012], Ans. (a) Refer to Basic Concept Point 4 (Megagametogenesis)., (b) For diagram refer to Fig. 2.14., , 64

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Q. 10. (a) Explain the post-pollination events leading to seed production in angiosperms., (b) List the different types of pollination depending upon the source of pollen grain. , , [CBSE Delhi 2016], Ans. (a) Refer to Basic Concepts Points 6, 8 and 9., (b) The different types of pollination are:, (i) Autogamy/self-pollination, (ii) Geitonogamy., (iii) Xenogamy/cross-pollination., Q. 11., , (a) Describe any two devices in a flowering plant which prevent both autogamy and, geitonogamy., (b) Explain the events upto double fertilisation after the pollen tube enters one of the synergids, in an ovule of an angiosperm., [CBSE 2018], Ans. (a) (i) Dioecy: It refers to the production of unisexual flowers in different plants., (ii) Self-incompatibility: It refers to the condition where pollens fail to pollinate the stigma, of same flower., (b) Refer to Basic Concepts Point 8., Q. 12., , (a) Explain the characteristic features of wind-pollinated flowers. How are insect-pollinated, flowers different from them?, (b) Explain the mutually rewarding relationship between Yucca plant and a species of moth. , , [CBSE (F) 2011], Ans. (a) Wind-pollinated flowers have light-weight, non-sticky, dry and winged pollens. The wellexposed stamens help in easy dispersal of pollen grains. The stigma is sticky, large and, feathery to trap pollen grains floating in the air. Numerous flowers are packed together to, form inflorescence., Insect-pollinated flowers are large, sticky and brightly coloured with honey and nectar, glands to attract insects. They are highly fragrant and the stigma is sticky., (b) Both Yucca plant and the moth cannot complete their life cycles without each other. The moth, deposits its eggs in the locule of the ovary and the flower in turn, gets pollinated by the moth., The larvae of the moth come out of the eggs as the seeds start developing., Q. 13. Make a list of any three outbreeding devices that flowering plants have developed and explain, how they help to encourage cross-pollination., [CBSE (AI) 2014], Ans. (i) Production of unisexual flowers/dioecious plants, cross pollination ensured., (ii) Self incompatibility, genetic mechanism prevent the pollen germination on the stigma of the, same flower., (iii) Anther and stigma are placed at different positions, so the pollen can not come in contact, with the stigma of the same flower., Q. 14., , (a) Plan an experiment and prepare a flow chart of the steps that you would follow to ensure, that the seeds are formed only from the desired sets of pollen grains. Name the type of, experiment that you carried out., (b) Write the importance of such experiments., [CBSE (AI) 2015], Ans. (a) Selection of flowers from desired plants, emasculation, bagging, dusting of the, pollens on the stigma of the flowers that were bagged (pollination), rebagging of flower, fruit formed, The name of the experiment is Artificial hybridisation., (b) (i) Production of superior or improved varieties of plants. (ii) Improves crop yield., Q. 15. (a), (b), Ans. (a), (b), , Draw a labelled long-sectional view of albuminous ‘seed’., How are seeds advantageous to flowering plants?, Refer to Fig. 2.15(c) and (d)., Refer to Basic Concepts Point 9 (Advantages of seeds)., , [CBSE (AI) 2010], , Sexual Reproduction in Flowering Plants 65

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Q. 16. (a), (b), (c), Ans. (a), , Explain the different ways apomictic seeds can develop. Give an example of each., Mention one advantage of apomictic seeds to farmers., Draw a labelled mature stage of a dicotyledonous embryo., [CBSE (AI) 2014], (i) Diploid egg cell is formed without reduction division and develops into embryo without, fertilisation, e.g., Asteraceae/grasses., (ii) In citrus/mango, some of the diploid nucellar cells surrounding the embryo sac start, dividing, protrude into embryo sac and develop into a embryo., (b) No segregation of character in hybrid seeds, economically beneficial and desired varieties are, cultivated., (c) Refer to Fig. 2.14., Q. 17. Explain the events upto fertilisation that occur in a flower after the pollen grain has landed on, its compatible stigma., [CBSE (F) 2016], Ans. When pollen grain lands over the stigma, it starts germinating and produces a pollen tube, through a germ pore. Pollen tube passes through style and reaches the ovule. The generative, cell divides and forms two male gametes. Finally the pollen tube enters the embryo sac through, micropyle. Now the pollen tube enters the egg apparatus through one of the synergids with, the help of filiform apparatus. The vegetative nucleus degenerates while pollen tube leaves two, male gametes in embryo sac. Now one of the male gamete fuses with the egg cell to form diploid, zygote known as syngamy. The other male gamete fuses with the two already fused polar nuclei, (called secondary nucleus) and forms triploid primary endosperm nucleus (PEN) which later, gives rise to endosperm. This is called triple fusion. Hence syngamy and triple fusion together, are known as double fertilisation., For diagram refer to Fig. 2.12., Q. 18. (a) Explain the events after pollination leading to the formation of a seed in angiosperms., (b) Mention the ploidy levels of the cells of different parts of an albuminous seed. , , [CBSE (F) 2015], Ans. (a) Refer to Basic Concepts Points 6 and 8., (b) The embryo is diploid (2n) and the endosperm is triploid (3n)., Q. 19. (a) Explain the phenomenon of double fertilisation., (b) Draw a labelled diagram of a typical anatropous ovule., [CBSE Delhi 2014], Ans. (a) Double fertilisation includes syngamy where one of the male gametes fuses with egg cell to, form zygote and triple fusion which includes fusion of second male gamete with two polar, nuclei., (b) Refer to Fig. 2.7., Q. 20., , (a) Draw a L.S. of a pistil showing pollen tube entering the embryo sac in an angiosperm and, label any six parts other than stigma, style and ovary., (b) Write the changes a fertilised ovule undergoes within the ovary in an angiosperm plant. , , [CBSE (AI) 2013], Ans. (a) Refer to Fig. 2.12 (a)., (b) In a fertilised ovule, following changes occur:, (i) Zygote changes into embryo, (ii) Integument develops into the seed coat, (iii) Synergids and antipodals degenerate, (iv) Ovule changes to form the seed., , 66

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Q. 21., , (a) Draw a schematic labelled diagram of a fertilised embryo sac of an angiosperm., , (b) Describe the stages in embryo development in a dicot plant., Ans. (a) Refer to Fig. 2.13(a)., (b) For explanation refer to Basic Concepts Point 9 (Embryogeny in Dicots)., Q. 22., , (a) As a senior biology student you have been asked to demonstrate to the students of, secondary level in your school, the procedure(s) that shall ensure cross-pollination in a, hermaphrodite flower. List the different steps that you would suggest and provide reasons, for each one of them., (b) Draw a diagram of a section of a megasporangium of an angiosperm and label funiculus,, micropyle, embryo sac and nucellus., [CBSE (AI) 2016], Ans. (a) The following steps would be followed:, (i) Emasculation or removal of anthers from the flower bud, before the anther dehisce, to, avoid self pollination., (ii) Bagging, to prevent contamination of its stigma with unwanted pollen grains., (iii) Rebagging, the stigma of the mature ovary are dusted with desired pollen grains and, rebagged to allow the fruit to develop., (b) For diagram refer to Fig. 2.7., Q. 23. (a) Why is the process of fertilisation in angiosperms termed as double fertilisation? Explain., (b) Draw a diagram of an angiospermic embryo sac where fertilisation is just completed., Label the following parts:, (i) Micropylar end of the embryo sac., (ii) The part that develops into an embryo., (iii) The part that develops into an endosperm., (iv) The degenerating cells at the chalazal end., (c) Draw a labelled diagram of globular embryonic stage of an angiosperm. [CBSE (F) 2011], Ans. (a) In angiosperms, fusion of haploid egg cell with one haploid male gamete to form diploid, zygote is called syngamy. Also, fusion of two (diploid) polar nuclei with the other haploid, male gamete to form triploid primary endosperm nucleus is called triple fusion. Hence, the, fertilisation is referred to as double fertilisation., (b) Refer to Fig. 2.13(a)., (c) Refer to Fig. 2.13(b)., Q. 24., , (a) Name the structures which the parts ‘A’ and ‘B’ shown in the diagram below respectively, develop into., (b) Explain the process of development which ‘B’ undergoes in albuminous and exalbuminous, seeds. Give one example of each of these seeds., [CBSE (F) 2011], , Sexual Reproduction in Flowering Plants 67

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Ans. (a) A develops into an embryo; B develops into endosperm., (b) Refer to Basic Concepts Point 9 (Endosperm Development)., Q. 25., , (a) Draw a labelled diagram of L.S. of a flower to show the growth of pollen tube reaching egg, apparatus., (b) Pistil of a flower does not accept pollen from any plant other than from its own kind. How, does it happen? Explain., Ans. (a) Refer to Fig. 2.12(a)., (b) The pistil has the ability to recognise pollen, whether it is of right type (compatible) or of the, wrong type (incompatible). It is mediated by chemical components of the pollen interacting, with those of the pistil., Q. 26. Explain double fertilisation and trace the post-fertilisation events in sequential order leading, to seed formation in a typical dicotyledonous plant., [CBSE (F) 2010], Ans. Double fertilisation: Refer to Basic Concepts Point 8., Following are the post-fertilisation events:, (i) Development of embryo: Embryo develops in fertilised ovule, from the zygote. The early, stages of embryo development from a zygote is known as embryogeny. The formation of, embryo starts only after certain amount of endosperm formation has taken place to assure, the nutrition supply, for development and growth of embryo., (ii) Development of seeds: Refer to Basic Concepts Point 9 (Embryogeny in Dicots)., As a result of double fertilisation number of changes takes place in an ovule due to which, ovule is converted into seeds., Q. 27., , (a) Why does endosperm development precede embryo development in angiosperm seeds?, State the role of endosperm in mature albuminous seeds., (b) Describe with the help of three labelled diagrams the different embryonic stages that, include mature embryo of dicot plants., [CBSE Delhi 2014], Ans. (a) Endosperm development precedes embryo development because endosperm provides, nutrition for the developing embryo. It is an adaptation to provide assured nutrition to the, developing embryo., The endosperm provides nutrition during seed germination., (b) The zygote (in the embryo sac) divides to give rise to pro embryo and subsequently to the, globular, heart shaped and mature embryo as shown in the diagram., Refer to Fig. 2.13 (b)., Q. 28. Give reasons why:, (i) most zygotes in angiosperms divide only after certain amount of endosperm is formed., (ii) groundnut seeds are exalbuminous and castor seeds are albuminous., (iii) micropyle remains as a small pore in the seed coat of a seed., (iv) integuments of an ovule harden and the water content is highly reduced, as the seed, matures., (v) apple and cashew are not called true fruits., [CBSE (AI) 2011] [HOTS], Ans. (i) To obtain nutrition from the endosperm for the developing embryo, zygotes, divide after its, formation., (ii) The groundnut seeds are exalbuminous because the endosperm is completely consumed, during embryo development. Whereas, castor seeds are albuminous because the endosperm, persists and is used up during seed germination., (iii) Micropyle remain as a small pore in the seed coat of a seed for the entry of water and oxygen, required for germination., , 68

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(iv) To protect the embryo and keep the seed viable, until favourable conditions return for, germination., (v) In apple and cashew, apart from ovary, thalamus also contributes to fruit formation so they, are not true fruits., Q. 29. A flower of tomato plant following the process of sexual reproduction produce 240 viable, seeds., Answer the following questions giving reasons:, (a) What is the minimum number of pollen grains that must have been involved in the, pollination of its pistil?, (b) What would have been the minimum number of ovules present in the ovary?, (c) How many megaspore mother cells were involved?, (d) What is the minimum number of microspore mother cells involved in the above case?, (e) How many male gametes were involved in this case?, [CBSE Delhi 2015] [HOTS], Ans. (a) 240 pollen grains. One pollen grain participates in fertilisation of one ovule., (b) 240 ovules. One ovule after fertilisation forms one seed, (c) 240 MMC were involved. Each MMC forms four megaspores out of which only one remains, functional., (d) 60 MMCs (240/4 = 60). Each microspore mother cell meiotically divides to form four pollen, grains., (e) 480 male gametes (240 × 2 = 480). Each pollen grain carries two male gametes (which, participate in double fertilisation), Q. 30. A flower of brinjal plant following the process of sexual reproduction produces 360 viable, seeds., Answer the following questions giving reasons:, (a) How many ovules are minimally involved?, (b) How many megaspore mother cells are involved?, (c) What is the minimum number of pollen grains that must land on stigma for pollination?, (d) How many male gametes are involved in the above case?, (e) How many microspore mother cells must have undergone reduction division prior to, dehiscence of another in the above case?, [CBSE Delhi 2015] [HOTS], Ans. (a) 360 ovules are involved. One ovule after fertilisation forms one seed., (b) 360 MMC are involved. Each MMC forms four megaspores out of which only one remains, functional., (c) 360 pollen grains. One pollen grains participates in fertilisation of one ovule., (d) 720 male gametes are involved. Each pollen grain carries two male gametes (which participate, in double fertilisation) (360 × 2 = 720)., (e) 90 MMC undergo reduction division. Each microspore mother cell meiotically divides to, form four pollen grains. (360/4 = 90)., Q. 31., , (a) A capsicum flower has 240 ovules in its ovary. But, it produces a fruit with only 180 viable, seeds., Explain giving a reason that could be responsible for such a result., (b) Describe the development of an endosperm in a viable seed. Why does endosperm, development precede embryo development?, (c) Give an example of an angiosperm seed that has a perisperm. Name the part the perisperm, develops from. , [CBSE Delhi 2017], , Sexual Reproduction in Flowering Plants 69

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Ans. (a) (i) 240 ovules giving rise to only 180 viable seeds, can be possible only if less number of, pollen grains or male gametes were available., (ii) All pollen grains did not germinate or did not form pollen tubes., (iii) Many pollen were not compatible, (b) For the development of an Endosperm, Refer to Basic Concepts Point 9., Cells of endosperm are filled with reserve food materials that are used for nutrition of, developing embryo. Thus endosperm needs to develop before embryo., (c) Black pepper and beet have a perisperm. The perisperm develop from the nucellus., Q. 32. Rose plants produce large, attractive bisexual flowers but they seldom produce fruit. On the, other hand, Lady’s finger produces plenty of fruits. Analyse the reasons for failure of fruit, formation in rose., Ans. Failure of fruit formation in rose may be due to several reasons. Some of them are:, (a) Inability to produce viable pollens., (b) Absence of functional egg., (c) Presence of abortive ovules., (d) Being hybrids, the meiotic process may be abnormal resulting in non-viable gametes., (e) There may be self-incompatibility., (d) There may be internal barriers for pollen tube growth and/or fertilisation., Q. 33. (a) Seeds offer several advantages to angiosperms. Describe any three such advantages., (b) Why is banana called a parthenocarpic fruit? Would you call banana a true fruit? Give, reason in support of your answer., Ans. (a) Reproductive processes such as pollination and fertilisation are independent of water., Following are their advantages:, (i) Better adaptive strategies for dispersal to new habitats., (ii) Hard seed coat provides protection to young embryo ., (iii) Sexual reproduction—new genetic combinations., (iv) Sufficient food reserves for the seedling., (v) Basis of agriculture–storage of seeds can occur due to seed habit-dehydration and, dormancy. , (Any three), (b) Banana fruit develops without fertilisation therefore, it is called parthenocarpic fruit., Yes, it is a true fruit because it develops from ovary., , 70

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Self-Assessment Test, Time allowed: 1 Hour, , Max. marks: 30, , 1. Choose and write the correct option in the following questions., (3×1 = 3), (i) Among the terms listed below, those that of are not technically correct names for a floral whorl, are, A. androecium, , B. carpel, , C. corolla , , D. sepal, , (a) A and D , , (b) C and D, , (c) B and D , , (d) A and B, , , , (ii) Which of the following is true for typical bilobed anther?, , (a) 2 theca, 2 sporangia, , (b) 4 theca, 4 sporangia, , (c) 4 theca, 2 sporangia, , (d) 2 theca, 4 sporangia, , (iii) The outermost and innermost wall layers of microsporangium in an anther are respectively , , [NCERT Exemplar], (a) endothecium and tapetum, , (b) epidermis and endodermis, , (c) epidermis and middle layer, , (d) epidermis and tapetum, , 2. In the following questions a statement of assertion followed by a statement of reason is given., Choose the correct answer out of the following choices. , (3×1 = 3), (a) Assertion and reason both are correct statements and reason is correct explanation for assertion., , , (b) Assertion and reason both are correct statements but reason is not correct explanation for, assertion., , , , (c) Assertion is correct statement but reason is wrong statement., , , , (d) Assertion is wrong statement but reason is correct statement., (i) Assertion : Microspores are formed from microspore mother cells by mitosis., Reason, , : Microspore form pollen grain when anthers mature., , (ii) Assertion : In angiosperms, the mature embryo sac is said to be 8-nucleate., , , Reason, , : In mature embryo sac there are 3 nuclei at chalazal end, 3 nuclei at micropylar, end and 2 nuclei in the central cell., , (iii) Assertion : Epicotyl develops into radicle on root tip., Reason, , : A dicot embryo consist of two cotyledons., , 3. What is self-incompatibility? , , (1), , 4. Banana is a parthenocarpic fruit whereas oranges show polyembroyony. How are they different, from each other with respect to seeds? , (1), 5. Explain giving two reasons why pollen grains can be best preserved as fossils.[CBSE (F) 2010] (2), 6. “Pollen grains have some harmful effects”. Discuss. , , (2), , 7. How many haploid cells are present in a mature female gametophyte of a flowering plant? Name, them. , (2), 8. Draw a labelled diagram of L.S. of an apple. , , (2), , 9. List three strategies that a bisexual flower can evolve to prevent self-pollination., , (3), , 10. Trace the development of female gametophyte (embryo sac) from megaspore mother cell in a, flower. Give a labelled diagram of the final stage of female gametophyte., (3), , Sexual Reproduction in Flowering Plants 71

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11. Observe the diagram of pollination by water in Vallisneria., , Answer the following questions based on the diagram., , , , , (3×1 = 3), , (i) The following statements (a), (b) and (c) seem to describe the water-pollinated submerged, plants. Which one of these statements is incorrect?, , (a) The flowers do not produce nectar., (b) The pollen grains have mucilaginous covering., (c) The brightly coloured female flowers have long stalk to reach the surface., , , (ii) Mention the pollinating agent of an inflorescence of small dull coloured flowers with well, exposed stamens and large feathery stigma. Give any one characteristic of pollen grains, produced by such flowers., , (iii) Name the type of pollination as a result of which genetically different types of pollen grains of, the same species land on the stigma., 12., , , (i) State one difference and one similarity between geitonogamy and xenogamy., (ii) Explain any three devices developed in flowering plants to discourage self-pollination and, encourage cross-pollination. , (5), , Answers, 1. (i)—(c), (ii)—(d), (v)—(d) , , 2. (i)—(d), (ii)—(a), (iii)—(d), zzz, , 72