NCERT Solutions for Class 12 Biology Chapter 1 Sexual Reproduction in Flowering Plants

1. Name the parts of an angiosperm flower in which the development of male and female gametophytes takes place.

Ans: In pollen sacs of the anther, male gametophytes (microgametogenesis) develop up to the 2-celled stage. The nucellus of an ovule is where the gametophyte develops (megagametogenesis).

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: Microsporogenesis and megasporogenesis differ in the following ways:

Meiotic cell Division occurs during microsporogenesis and megasporogenesis. It leads to the production of haploid gametes, also known as reductional division.

3. Arrange the following terms in the correct developmental sequence: Pollen grain, sporogenous tissue, microspore tetrad, pollen mother cell, male gametes.

Ans: The sporogenous tissue is composed of a pollen mother cell, a microspore tetrad, pollen grains, and male gametes.

4. With a neat, labeled diagram, describe the parts of a typical angiosperm ovule.

Ans:

An angiosperm ovary is capable of forming a small structure called an ovule. Nucellus, a multi-layered cellular tissue, develops as the ovule first appears on the placenta. Placentas are attached to ovules via a stalk known as a funicle. A funicle attaches to a placenta at the hilum. The hypodermal cells of the nucellus enlarge and transform into megaspore mother cells. One haploid cell undergoes meiosis to form an embryo sac (female gametophyte). The others do not develop. A pollen tube enters an ovule through a small opening called a micropyle, surrounded by one or two protective layers. Ovules consist of the nucellus and integuments of a fully developed embryo.

5. What is meant by monosporic development of female gametophytes?

Ans: The female gametophyte or embryo sac develops only from one of the four megaspores in many flowering plants. Degeneration occurs in the three remaining megaspores. The monosporic type of embryo sac formation is referred to as the monosporic type of embryo development.

6. A neat diagram explains the 7-celled, 8-nucleate nature of the female gametophyte.

Ans: 

• Two nuclei form after the first mitotic division and move towards the micropylar and chalazal end, respectively.

• Division and redivision occurs to form 8-nucleate stage and consequently there are four nuclei, each on either end.

• A typical female gametophyte or embryo sac is formed after the 8-nucleate stage. The antipodal and micropylar end of each of the eight nuclei comprises the six nuclei grouped. Two synergids and an egg cell are at the centre of the egg apparatus. 

• The polar nuclei are located within the large central cell of the embryo sac just below the egg apparatus. A typical female gametophyte comprises seven cells with eight nuclei, as both polar nuclei are present within the same cell.

7. What are chasmogamous flowers? Can cross-pollination occur in cleistogamous flowers? Give reasons for your answer.

Ans: The anther and stigma of chasmogamous flowers are exposed for pollination. Cleistogamous flowers are incapable of cross-pollination. Therefore, only self-pollination is caused by these closed flowers. During the dehiscence process of cleistogamous flowers, anthers dehisce into closed flowers. As a result, pollen grains are exposed to stigma. Therefore, it is impossible for cross-pollination to occur, such as Oxalis and Viola.

8. Mention two strategies evolved to prevent self-pollination in flowers

Ans: An individual race's vigor and vitality are diminished by continuous self-pollination. In order to prevent self-pollination and to promote cross-pollination, flowering plants have developed many devices. Cross-pollination is most frequently ensured by dichogamy and self-sterility.

Dichogamy: Different maturation times for the anthers and stigmas prevent self-pollination.

Self-sterility (or self-incompatibility): pollen grains from some flowers do not germinate on their stigma due to the presence of self-sterility genes. Examples include tobacco and potatoes.

9. What is self-incompatibility? Why does self-pollination not lead to seed formation in self-incompatible species?

Ans: On its stigma, a flower that does not produce pollen grains is incompatible or self-sterile. This condition is called self-incompatibility or self-sterility. It is called pollination when pollen grains are transferred from the stigma to the anthers. As a result of this transference, seeds are formed. The process of self-pollination occurs when pollen grains are shed from the anther in the same flower to the stigma in the same flower. Some flowers, however, do not produce seeds when self-pollination occurs because they contain the same sterile gene on the pistil and pollen grain. Since pollen grains cannot germinate, male gametes cannot fertilize egg cells. This prevents the ovule from developing into a seed.

10. What is a bagging technique? How is it useful in a plant breeding program?

• Ans: When applied to emasculated flowers (which are in the bud stage), a bag of polythene butter paper prevents pollen contamination of its stigmas. Emasculated flowers can be removed from their buds and stuffed into a butter paper bag before anthesis. 

• A pre-sterilized brush is used to dust the stigmas of mature emasculated flowers with pollen grains of desired male plants. Flowers are then re-bagged until the fruits are formed. 

• Artificial hybridisation uses this technique primarily. Plant breeders use this technique to prevent unwanted pollen grains from contaminating the stigma of flowers.

11. What is triple fusion? Where and how does it take place? Name the nuclei involved in triple fusion.

Ans: Triple fusion is a process by which male gamete fuses with two polar nuclei within the embryo sac of Flowering Plants. The events taking place in triple fusion are:

• The pollen grain germinates by getting dusted on the stigma and giving rise to a pollen tube that enters the ovule.

• The pollen tube passes into one of the synergids and releases two male gametes one of which fuses with the egg nucleus and forms a zygote.

• The other gamete fuses with the two polar nuclei located in the central cell and forms a triploid endosperm nucleus.

12. Why do you think the zygote is dormant for some time in a fertilized ovule?

Ans: Zygotes become embryos after resting for a while. Until some amount of endosperm forms, most zygotes remain dormant. Developing embryos need this nutrition to grow and develop properly.

13. Differentiate between:

(a) Hypocotyl and epicotyl;

(b) Coleoptile and coleorhiza;

(c) Integument and testa;

(d) Perisperm and pericarp.

Ans:

(a) Hypocotyl and Epicotyl;

(b) Coleoptile and Coleorhiza;

 (c) Integument and Testa;

(d) Perisperm and Pericarp.

14. Why is an apple called a false fruit? Which part(s) of the flower forms the fruit?

Ans: True fruit is an ovary that has ripened botanically. Often called false fruits, these are fruits in which the thalamus, floral parts, and ovary are present. Apple is derived from the thalamus and is hence called a false fruit.  Mainly the fleshy thalamus of apples can be eaten—the ovaries from a parthenocarpic fruit after or without fertilisation.

15. What is meant by emasculation? When and why does a plant breeder employ this technique?

Ans: The stem of a flower bud is systematically excised to remove the anthers and stamens before they die. In order to minimize self-pollination, this is done. Hybridization by artificial means includes emasculation. This method is used by plant breeders to prevent the pollination of adjacent flowers and pollinate stigmas with pollen of the desired variety.

16. If one can induce parthenocarpy through the application of growth substances, which fruits would you select to induce parthenocarpy and why?

Ans: The fruit of the parthenocarpy is seedless. The ovary does not fertilize them before they develop. A few seedless fruits are of great economic importance, such as banana, grape, orange, pineapple, guava, watermelon, and lemon. In fruits with edible seeds or seeds (e.g., pomegranates), parthenocarpy is not selected.

17. Explain the role of tapetum in the formation of pollen-grain walls.

Ans: Microsporangia are surrounded by a thin layer called the tapetum. Multinucleated and polyploidy tapetal cells make up the tissue. Pollen grains develop as a result of them. Ubisch bodies are found in these cells and contribute to the ornamentation of the microspores and pollen grains. Sporopollenin is a substance produced by the Ubisch bodies of the tapetal cells. This substance is present on the exine layer of pollen grains. A spiny appearance is attributed to the exine of pollen grains due to the presence of this compound.

18. What is apomixis and what is its importance?

Ans: The asexual reproduction process of apomixis results in seeds without fertilization, such as in certain species of Asteraceae and Grasses. The hybrid seed industry relies on this method. Increasing productivity is the leading reason for cultivating hybrids. However, the main problem is the need to grow hybrid seeds annually since seeds from hybrid plants do not preserve hybrid characteristics for long periods because of the segregation of characters. By introducing apomixis into hybrid seeds, this can be avoided. As a result, scientists are seeking genes associated with apomixis.

Topics Covered in Biology Class 12 Chapter 1 Sexual Reproduction In Flowering Plants

Key Features of NCERT Biology Class 12 Chapter 1 Sexual Reproduction in Flowering Plants Solutions 

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Conclusion

NCERT Solutions for Chapter 1, Sexual Reproduction in Flowering Plants, forms the foundation for understanding Plant Reproduction. Biology Class 12 Chapter 1 weightage can vary depending on the exam boards, but students can expect 4-6 questions from this Chapter. Students can access Sexual Reproduction in Flowering Plants Class 12 PDF that helps clear their doubts from the 12th biology 1st chapter exercise.

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