CBSE/NCERT/Exercises/Class_12_Biology
Created by Titas Mallick
Biology Teacher • M.Sc. Botany • B.Ed. • CTET (CBSE) • CISCE Examiner
Created by Titas Mallick
Biology Teacher • M.Sc. Botany • B.Ed. • CTET (CBSE) • CISCE Examiner
NCERT Biology Exercises for Class 12 Biology - Sexual Reproduction in Flowering Plants - Class_12_Biology
1. Name the parts of an angiosperm flower in which development of male and female gametophyte take place. Answer: The development of the male gametophyte (pollen grain) takes place in the anther (specifically within the microsporangia/pollen sacs). The development of the female gametophyte (embryo sac) takes place in the ovary (specifically within the ovule/megasporangium).
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. Answer:
3. Arrange the following terms in the correct developmental sequence: Pollen grain, sporogenous tissue, microspore tetrad, pollen mother cell, male gametes. Answer: Sporogenous tissue → Pollen mother cell → Microspore tetrad → Pollen grain → Male gametes.
4. With a neat, labelled diagram, describe the parts of a typical angiosperm ovule. Answer: (Description based on diagram 1.7d) A typical ovule (anatropous) consists of:
5. What is meant by monosporic development of female gametophyte? Answer: In a majority of flowering plants, only one of the four megaspores is functional while the other three degenerate. The development of the female gametophyte (embryo sac) from this single functional megaspore is called monosporic development.
6. With a neat diagram explain the 7-celled, 8-nucleate nature of the female gametophyte. Answer: The mature embryo sac consists of:
7. What are chasmogamous flowers? Can cross-pollination occur in cleistogamous flowers? Give reasons for your answer. Answer: Chasmogamous flowers have exposed anthers and stigma, similar to flowers of other species. Cross-pollination cannot occur in cleistogamous flowers because they never open. In these flowers, the anthers and stigma lie close to each other, ensuring only autogamy (self-pollination).
8. Mention two strategies evolved to prevent self-pollination in flowers. Answer:
9. What is self-incompatibility? Why does self-pollination not lead to seed formation in self-incompatible species? Answer: Self-incompatibility is a genetic mechanism that prevents self-pollen from the same flower or other flowers of the same plant from fertilizing the ovules. It does not lead to seed formation because it inhibits pollen germination or pollen tube growth, preventing fertilization.
10. What is bagging technique? How is it useful in a plant breeding programme? Answer: Bagging involves covering the stigma of a flower with a bag (usually made of glycine or butter paper) to prevent contamination by unwanted pollen. In artificial hybridization, it ensures that only the desired pollen is used for pollination, which is crucial for producing specific hybrid varieties.
11. What is triple fusion? Where and how does it take place? Name the nuclei involved in triple fusion. Answer: Triple fusion is the fusion of the second male gamete with the two polar nuclei (or the secondary nucleus) in the central cell of the embryo sac. It takes place in the embryo sac. The nuclei involved are one haploid male gamete and two haploid polar nuclei (resulting in a triploid primary endosperm nucleus).
12. Why do you think the zygote is dormant for sometime in a fertilised ovule? Answer: The zygote remains dormant for a short period to allow for the initial development of the endosperm. Since endosperm provides nourishment to the developing embryo, its formation always precedes the development of the embryo to ensure a continuous food supply.
13. Differentiate between: (a) hypocotyl and epicotyl: Epicotyl is the portion of embryonal axis above the level of cotyledons, while hypocotyl is the portion below. (b) coleoptile and coleorrhiza: Coleoptile is a protective sheath covering the plumule (shoot tip) in monocots, while coleorrhiza covers the radicle and root cap. (c) integument and testa: Integument is the protective envelope of the ovule, which hardens after fertilization to become the testa (seed coat). (d) perisperm and pericarp: Perisperm is the persistent residual nucellus in some seeds (e.g., black pepper), while pericarp is the wall of the fruit developed from the ovary wall.
14. Why is apple called a false fruit? Which part(s) of the flower forms the fruit? Answer: Apple is called a false fruit because the fruit develops not just from the ovary, but also from the thalamus which contributes to its formation. In most fruits, only the ovary develops into the fruit.
15. What is meant by emasculation? When and why does a plant breeder employ this technique? Answer: Emasculation is the removal of anthers from the floral bud of a bisexual flower before they dehisce. A plant breeder employs this technique in artificial hybridization to prevent self-pollination and ensure that the stigma is only pollinated with the desired pollen grains.
16. If one can induce parthenocarpy through the application of growth substances, which fruits would you select to induce parthenocarpy and why? Answer: One would select fruits like banana, grapes, or oranges. Parthenocarpy produces seedless fruits, which are highly desirable for consumption and commercial purposes in these specific varieties.
17. Explain the role of tapetum in the formation of pollen-grain wall. Answer: The tapetum is the innermost wall layer of the microsporangium. It nourishes the developing pollen grains and secretes various substances, including precursors for sporopollenin, which is the key component of the hard outer wall (exine) of the pollen grain.
18. What is apomixis and what is its importance? Answer: Apomixis is a form of asexual reproduction that mimics sexual reproduction, where seeds are produced without fertilization. Its importance lies in the hybrid seed industry; if hybrids are made into apomicts, farmers can reuse the seeds year after year as the characters will not segregate in the progeny.
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