1. Name the parts of an angiosperm flower in which development of male and female gametophytes take place.
2. Differentiate between microsporogenesis and megasporogenesis. What type of cell division occurs during these events? Name the structures formed at the end of these two events.
3. Arrange the following terms in the correct developmental sequence: Pollen grain, sporogenous tissue, microspore tetrad, pollen mother cell, male gametes.
4. With the help of a neat, labelled diagram, describe the parts of a typical angiosperm ovule.
5. What is meant by monosporic development of female gametophytes?
6. With a neat diagram explain the 7-celled, 8-nucleate nature of the female gametophyte.
7. What are chasmogamous flowers? Can cross-pollination occur in cleistogamous flowers? Give reasons for your answer.
8. Mention two strategies evolved to prevent self-pollination in flowers.
9. What is self-incompatibility? Why does self-pollination not lead to seed formation in self-incompatible species?
10. What is a bagging technique? How is it useful in a plant breeding programme?
11. What is triple fusion? Where and how does it take place? Name the nuclei involved in triple fusion.
12. Why do you think the zygote is dormant for some time in a fertilised ovule?
13. Differentiate between:
    1. hypocotyl and epicotyl
    2. coleoptile and coleorhiza
    3. integument and testa
    4. perisperm and pericarp
14. Why is an apple called a false fruit? Which part(s) of the flower forms the fruit?
15. What is meant by emasculation? When and why does a plant breeder employ this technique?
16. If one can induce parthenocarpy through the application of growth substances, which fruits would you select to induce parthenocarpy and why?
17. Explain the role of tapetum in the formation of pollen-grain walls.
18. What is apomixis and what is its importance?

NCERT Solutions For Class 12 Biology Chapter 2:

1. Male gametophyte development (microgametophyte) occurs in the pollen sac of anthers up to the 2-cell stage. Female gametophytes develop in the nucleus of the ovule (megagametophytes).

2. The differences between microsporogenesis and megasporogenesis are as follows:
   
   

   Microsporogenesis	Megasporogenesis
   It is the process by which a diploid microspore mother cell goes through meiosis to produce haploid microspores.	It is the process through which haploid megaspores are produced from a diploid mother cell.
   Microsporogenesis is the process through which pollen is formed.	Megasporogenesis is the process through which embryo sacs are formed.
   The process happens in the pollen sac.	The process happens inside ovules.
   A tetrad's microspore configuration is often tetrahedral.	Megaspores in a tetrad are often arranged in a linear pattern.
   Male gametophyte is formed as a result of the microspore.	Megaspore is responsible for the development of the female gametophyte.

   
   Both processes (microsporogenesis and megasporogenesis) involve the cell division process of meiosis or reduction division, which leads to the creation of haploid gametes from that of the mother cells of the microspore and megaspore.
   
   Microsporogenesis is the process by which haploid microspores are formed from a diploid microspore mother cell. Pollen is formed as a result of microsporogenesis. Megasporogenesis leads to the creation of haploid megaspores from a diploid megaspore mother cell. Embryo sac is created as a result of megasporogenesis.

3. The correct development sequence is as follows: Sporogenous tissue -> Pollen mother cell -> Microspore tetrad -> Pollen grain -> Male gametes During the development of the microsporangium, each cell of the sporogenous tissue acts as a pollen mother cell, ultimately leading to a microspore tetrad with four haploid microspores via the meiosis process (microsporogenesis). These microspores separate and grow into pollen grains as the anthers mature. Male gametes are produced as pollen grains develop.

4. The ovule is an integumented megasporangium that contains an embryo sac. The anatropous ovule is the most frequent form of angiosperm ovule. An anatropous ovule's structure is as follows:

   1. Funicle: The funicle or the stalk is a small, multicellular structure that connects the ovule's central part to the placenta.

   2. Hilum: It is the point at which the funicle connects to the main structure of the ovule.

   3. Nucellus: It is the major body of the ovule, which is made up of thin-walled parenchymatous cells. It provides nourishment to the growing embryo.

   4. Integuments: The nucellus is enveloped by one or two cellular coatings known as integuments. They are the protective outer layer of the ovule.

   5. Chalaza: It is a swollen area of the nucellus at the base.

   6. Micropyle: It is a small aperture at the top of the integuments. Along the micropyle, the pollen tube penetrates the embryo sac.

   7. Embryo sac: It is an oval sac found implanted in the nucellus near the micropylar end. It houses the egg apparatus and grows within the nucellus.

5. For most angiosperms, three of the four megaspores in a linear tetrad degenerate, leaving only one functioning. The functioning uninucleated megaspore divides three times to generate an 8-nucleated, 7-celled embryo sac. Monosporic development refers to the formation of a female gametophyte or embryo sac from a single uninucleated functioning megaspore. Four of the eight nuclei formed in the embryo sac are located at the micropylar end and four at the chalazal end. A single nucleus from every end pushes inside to generate two polar nuclei in the embryo sac's middle.

6. The embryo sac is the female gametophyte in angiosperms. It's a tiny oval structure with a three-celled egg apparatus, three antipodal cells, and one binucleate centre cell. As a result, the embryo sac is referred to as a 7-celled and 8-nucleated structure. The cells within the embryo sac are organised in a certain pattern. The egg apparatus is made up of three cells that are bunched at the micropylar side. The egg apparatus itself is made up of two synergids and one egg cell. Through plasmodesmata, the egg is linked to synergids. The synergids are distinctive cellular thickenings at the micropylar tip known as the filiform apparatus that help guide pollen tubes into the synergids.

7. Chasmogamous flowers have uncovered anthers and stigma, allowing for cross-pollination. Oxalis is an example of a chasmogamous flower. Cross-pollination is not possible in cleistogamous flowers because they are sealed and do not unfold in any way. Their anthers and stigma cannot be seen. As a result, pollen grains cannot be transferred from the exterior to the flower's stigma.

8. Pollen is transferred from the stamen to the pistil of the same flower during self-pollination. The following are the two techniques that have evolved to avoid self-pollination in flowers:

1. 1. In certain plants, the stigma of the flower has the potential to impede pollen grain germination and therefore the formation of the pollen tube. Self-incompatibility is a genetic mechanism that prevents self-pollination. Incompatibility can occur between members of the same species or between members of different species. As a result, incompatibility prohibits breeding.

   2. In certain plants, the androecium develops before the gynoecium, and vice versa. This is referred to as protogyny or protandry, depending on the gender. This prevents pollen from contacting the stigma of the same flower.

9. In angiosperms, self-incompatibility is a biological process that prohibits self-pollination. It causes a genetic mismatch between members of the same species or between members of divergent species. Plants that display this phenomenon have the potential to hinder pollen grain germination and, as a result, the formation of the pollen tube on the stigma of the flower. This inhibits the gametes from fusing and the embryo from developing. As a result, there is no seed formation.

10. Some artificial hybridization procedures involve emasculation or the removal of the anther from bisexual flowers without damaging the female reproductive portion (pistil). The emasculated flowers are then covered in bags to avoid undesired pollen grains from pollinating them. This is known as bagging. This approach is an important aspect of plant breeding procedure because it guarantees that only appropriate plant pollen grains are utilised for stigma fertilisation to generate the optimal plant type.

11. The merger of the male gamete with two polar nuclei within the angiosperm embryo sac is known as triple fusion. This fusion occurs within the embryo sac.

12. The zygote is created when the male gamete fuses with the nucleus of the egg cell. The zygote stays inactive for some time while it awaits the formation of the endosperm, which grows from the primary endosperm cell formed during triple fusion. The endosperm supplies nourishment for the developing embryo, and as the endosperm forms, the embryo develops farther from the zygote.

13. Differences are as follows:

    1. The hypocotyl is the part of the embryonal axis that is underneath the cotyledon in a dicot embryo. It has the radicle in the lower end. The epicotyl is the part of the embryonal axis that is above the cotyledon in a dicot embryo. It has the plumule in the lower end.

    2. A coleoptile is a cone-shaped protective covering that surrounds the plumule of a monocot seed. Coleorhiza is an unstructured sheath found in monocot seeds that completely covers the radicle and root cap.

    3. The ovule's integument is its outermost coat. It shields it from damage. A seed's testa is its outermost coat.

    4. Perisperm is the nucellus that remains after fertilisation. It may be found in seeds including beet and black pepper. The ripening wall of a fruit, which grows from the walls of an ovary, is known as the pericarp.

14. False fruits are fruits formed from the ovary and other supplementary floral components. Whereas true fruits are those that emerge from the ovary but do not include the thalamus or some additional floral elements. The fleshy receptacle of an apple is the major edible component. As such, it is known as a fake fruit.

15. Emasculation is a method used mostly in plant hybridization that involves detaching anthers from bisexual flowers without damaging the female reproductive portion (pistil). Agronomists use emasculation in bisexual flowers to acquire the required variation of a species by combining a specific plant with the appropriate pollen grain.

16. Parthenocarpy is the development of fruits without fertilisation or seed production. This technique is used to generate seedless types of commercially significant fruits such as orange, lemon, watermelon, and so on. This method involves the use of plant growth hormones such as auxins to stimulate fruit production.

17. Tapetum is the microsporangium's deepest layer. It feeds the pollen grains that are forming. During microsporogenesis, tapetum cells create a variety of enzymes, hormones, amino acids, and other nutrients essential for pollen grain formation. It also creates the exine layer of pollen grains, which is made up of sporopollenin.

18. Apomixis is a mechanism for seed production that does not involve meiosis or syngamy. It is crucial in the generation of hybrid seeds. Farmers face high costs while developing hybrid seeds through cultivation. Furthermore, because hybrid characteristics separate during meiosis, it is difficult to preserve hybrid characters by planting hybrid seeds. Apomixis avoids the loss of certain hybrid characteristics. It is also a low-cost way of seed production.

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