NCERT Solution Class 12th Biology Chapter – 2 Sexual Reproduction in Flowering Plants Question & Answer

NCERT Solution Class 12th Biology Chapter – 2 Sexual Reproduction in Flowering Plants 

NCERT Solution Class 12th Biology Chapter – 2 Sexual Reproduction in Flowering Plants Question & Answer Microsporogenesis, Megasporogenesis discuses Sexual Reproduction in Flowering Plants.

NCERT Solution Class 12th Biology Chapter – 2 Sexual Reproduction in Flowering Plants 

Chapter – 2

Sexual Reproduction in Flowering Plants

Question & Answer

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

Answer: In an angiosperm, the male gametes are developed within the anther. On the contrary, the female gametes are developed inside the ovules.

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: The important differences between microsporogenesis and megasporogenesis are mentioned below:

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

The structures formed at the end of these events are:

Microsporogenesis – Pollen grain

Megasporogenesis – Embryo sac

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

Answer: Following is the correct developmental sequence: Sporogenous tissue → pollen mother cell → microspore tetrad → pollen grain → male gamete. When the microsporangium is developing, every cell of the sporogenous tissue serves as a pollen mother cell, giving rise to a microspore tetrad possessing four haploid microspores through the meiosis process (microsporogenesis). When the anthers mature, these microspores dissociate and develop into pollen grains. The pollen grains mature and give rise to male gametes.

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

Answer:

A typical angiospermic ovule is a small structure which is formed in the ovary. Ovule first develops as a projection on the placenta and composed of multilayered cellular tissue called the nucellus. The hypodermal cell of die nucellus enlarges and transformed into megaspore mother cell. This cell undergoes meiosis to produce four haploid cells only one of which develops & forms embryo sac (female gametophyte). An ovule may be surrounded by one or two protective layers called integuments, leaving a small opening at one end termed as micropyle which acts as passage for the entry of the pollen tube into the ovule. Thus, a typical ovule consists of a fully developed embryo sac with the nucellus and integuments

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

Answer: Monosporic development is the development of female gametophyte from one functional megaspore. In angiosperms, a single diploid mother megaspore undergoes meiotic division to form four megaspores (haploid). Only one out of the four megaspores is functional that forms a female gametophyte, while the rest of the three degenerate.

6. With a neat diagram, explain the 7-celled, 8 nucleate nature of female gametophyte.
Answer:

The female gametophyte is formed by the mitotic division of the mother megaspore. The megaspore divides mitotically thrice to form 8 nucleate embryo sacs.The process of formation of 7-celled, 8 nucleate nature of female gametophyte is mentioned below:

• Two nuclei are formed after the cell undergoes first mitotic division.
• These two nuclei move towards the micropylar end and the chalzal end, respectively.
• They divide and redivide to form 8 nucleate stage.
• Consequently, there are four nuclei each on either ends.
• At the micropylar end, three out of the four nuclei differentiate into an egg cell and synergids.
• At the chalzal end, three out of the four nuclei differentiate as antipodal cells.
• The remaining cells, each from either ends move towards the centre and is known as polar nuclei.

Therefore on maturation, the female gametophyte looks like a 7-celled structure.

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

Answer: Chasmogamous flowers are the flowers that have open petals such that the reproductive organs are exposed to allow cross-pollination. Cleistogamous flowers are small, closed flowers with unexposed reproductive organs. Therefore, they cannot undergo cross-pollination. However, they undergo self-pollination since the stigma and anther are present near each other.

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

Answer: There are two strategies involved in preventing self-pollination in flowers:

• • Dichogamy – It refers to the production of male and female reproductive organs at different times in order to prevent self-fertilization.
  • Self-incompatibility – It is a genetically controlled mechanism in which pollen grains of a flower are unable to completely grow on the stigma of the same flower.

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

Answer: Self-incompatibility refers to a genetically controlled mechanism that prevents self-pollination and promote cross-pollination in flowers. Self-pollination cannot lead to the formation of seeds in a self-incompatible species. This happens because the pollens are unable to fertilize the ovules that would develop into an embryo and hence form seeds.

10. What is bagging technique? How is it helpful in a plant breeding programme?

Answer: The bagging technique is helpful in preventing fertilization of stigma by any undesired pollen by covering the emasculated flower (flower whose anther is removed) with a polybag or butter paper.The bagging technique is beneficial in the plant breeding programme. In this, only desired pollens are made to fertilize the stigma in order to produce plants with desired characteristics.

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

Answer: Triple fusion occurs when a male gamete fuses with two polar nuclei within the embryo sac of flowering plants.The following events take place in triple fusion:

• The pollen grains get dusted on stigma and germinate giving rise to a pollen tube that enters the ovule.
• The pollen tube passes into one of the synergids and release two male gametes.
• One out of the two gametes 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.

The nuclei involved in triple fusion are:

• • A male gamete nucleus
  • Two polar nuclei

12. Why do you think zygote is dormant for sometime in a fertilized ovule?

Answer:  The zygote remains inactive until the endosperm is formed as a result of triple fusion. The endosperm provides nutrition to the developing embryo and is formed from the primary endosperm cell that results from triple fusion.

13. Differentiate between:

1. Epicotyl and hypocotyl
2. Coleoptile and coleorrhiza
3. Integument and testa
4. Perisperm and pericarp

Answer:

1. Epicotyl and hypocotyl

2. Coleoptile and coleorrhiza

3. Integument and testa

4. Perisperm and pericarp

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

Answer: A false fruit is the one that is derived from some secondary parts and not from the ovary. Apple is derived from the thalamus and hence called a false fruit.

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

Answer: Emasculation refers to the removal of stamens from bisexual flowers done before the maturation of anther in order to avoid self-pollination in the flowers.This technique is employed when the breeder wants plants of desired characteristics.The flowers are bagged even before the anther mature. When the anther matures, the pollen grains are shed on the covered stigma and are allowed to pollinate with the flowers of the desired characteristics.

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

Answer: Parthenocarpy refers to the development of fruits without fertilization. The varieties of fruits such as watermelon, muskmelon, devoid of seeds, are in great demand. Therefore, these varieties will be developed by parthenocarpy.

17. Explain the role of tapetum in the formation of pollen grain wall.

Answer: Tapetum is the internal layer of microsporangium and plays an important role in the formation of pollen grain wall. It provides nutrition to the maturing pollen grains. Various amino acids, enzymes, and hormones are produced by tapetum cells that are essential for the maturation of pollen grains. Tapetum also forms the exine layer of pollen grains.

18. What is apomixis and what is its importance?

Answer: Apomixis is the process of seed formation without the occurrence of fertilization (process of meiosis and syngamy to be precise). It plays a vital role in the production of hybrid seeds. Apomixis inhibits the loss of desired characters in a hybrid. Also the process of production of hybrid seeds through cultivation is expensive. Therefore, apomixis is used for the production of hybrid seeds.