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 take 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.
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Microsporogenesis:
(i) In this process, haploid microspores are formed from diploid microspore mother cell or pollen mother cell (MMC or PMC).
(ii) It occurs inside the microsporangia or pollen sac of an anther.
(iii) There are many microspore mother cells in a microsporangium.
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(iv) The four microspores formed from a single microspore mother cell are generally arranged in a tetrahedral tetrad.
(v) All the four microspores arranged in a tetrahedral tetrad are functional.
(vi) The microspores give rise to male gametophyte.
Megasporogenesis:
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(i) In this process, haploid megaspores are formed from diploid megaspore mother cell (MMC).
(ii) It occurs inside the nucelius of ovule or megasporangium.
(iii) There is generally a single megaspore mother cell in a megasporangium.
(iv) The four megaspores formed from a megaspore mother cell are arranged in the form of a linear tetrad.
(v) Only one remain functional while the other three degenerates.
(vi) On the other hand, the functional megaspore gives rise to female gametophyte.
Meiosis occurs during micro and megasporogenesis. Microspores (pollen grains) are formed at the end of microsporogenesis and megaspores (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. 5. What is meant by monosporic development of a female gametophyte?
Ans. Out of the four megaspores, three degenerate and only one remain 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. Explain the 7-celled, 8-nucleate nature of the female gametophyte.
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 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.
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 self- pollination (dichogamy).
(ii) Production of unisexual flowers.
Q. 9. What is self-incompatibility? Why does self-pollination not lead to seed formation in self-incompatible species?
Ans. Self-incompatibility or self sterility is the inability of an intersexual or bisexual plant to produce viable seeds on self-pollination inspite of producing functional male and female gametes. Since, fertilisation does not take place; as a result no seeds are produced.
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 or polythene to avoid their contamination from foreign pollens during breeding programme.
Uses in plant breeding:
(i) Prevention of contamination of stigma of female flowers with foreign pollens.
(ii) Prevention of damage by animals.
(iii) Prevention of germination of foreign pollens over the stigma.
Q. 11. What is triple fusion? Where and how does it take place? Name the nuclei involved in triple fusion.
Ans. Triple fusion is a fertilisation that involves 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.
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 coleorrhiza
(c) Integument and testa (d) perisperm and pericarp.
Ans. (a)
Hypocotyl:
(i) The region of the embryonal axis that lies between the radicle and the point of attachment of cotyledons is called hypocotyl.
(ii) Hypocotyl pushes the seed above the soil in epigeal germination.
(iii) It is an important component of embryonic root system.
Epicotyl:
(i) The region of the embryonal axis that lies between the plumule and cotyledons is called epicotyl.
(ii) Epicotyl pushes the plumule above the soil in hypogeal germination.
(iii) It is an important component of embryonic shoot system.
(b) Coleoptile:
(i) The shoot apex and few leaf primordia are enclosed in a hollow foliar structure in epicotyl region in monocots and is called coleoptile.
(ii) It comes out of the soil.
(iii) It emerges from the soil, turns green and carries out photosynthesis.
Coleorrhiza:
(i) The radicle and root cap are situated at the lower end of embryonal axis into undifferentiated sheath called coleorrhiza.
(ii) It remains inside the soil.
(iii) It remains in the soil and is non-green in colour.
(c) Integument:
(i) It is the protective covering of the ovule (nucellus).
(ii) It is thin and living.
(iii) It is part of pre-fertilisation.
Testa:
(i) It is the protective covering of the seed.
(ii) It is thick and dead.
(iii) It is part of post-fertilisation.
(d)
Perisperm:
(i) It represents persistent remains of nucellus (of ovule) in the seed.
(ii) It is a part that belongs to seed.
(iii) It is usually dry.
Pericarp:
(i) It represents the wall of fruit formed by the ovarian wall.
(ii) It is a part that belongs to fruit.
(iii) 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 in 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.
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, water-melon, lemon, etc., should be selected as parthenocarpic fruits. Here seeds are irritant during eating of fruits so seeds are removed to make the fruits even more valuable.
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. The phenomenon of asexual reproduction that mimics sexual reproduction by formation of seed without fertilisation is called apomixis or agamospermy. It is noticed in some species of Asteraceae and grasses.
Importance:
(i) It maintains the hybrid vigour in crop plants.
(ii) It results in the formation of more than one embryo in a seed, i.e., polyembryony.