NCERT Solutions for Class 12 Biology Chapter 2 – Sexual Reproduction in Flowering Plants is important for the students appearing for board examinations and further. The answers to the questions mentioned in the textbook are explained in detail. The NCERT Solutions for Class 12 are provided by subject experts and the students can refer to these for their exam preparation.
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Name the parts of an angiosperm flower in which the development of male and female gametophyte take place.
Solution:In an angiosperm, the male gametes are developed within the anther. On the contrary, the female gametes are developed inside the ovules.
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.
Solution:The important differences between microsporogenesis and megasporogenesis are mentioned below:
Microsporogenesis Megasporogenesis It is the process in which a diploid microspore mother cell undergoes meiosis to form haploid microspores. It is the process of formation of haploid megaspores from the diploid mother cell. Occurs inside pollen sacs. Occurs inside ovules. Pollens are produced by microsporogenesis. Embryo sacs are produced by megasporgenesis. The arrangement of microspores is tetrahedral. The arrangement of megaspores is linear. All the four microspores formed are functional. Only one out of the four megaspores formed is functional.
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
Arrange the following terms in correct developmental sequence:Pollen grain, sporogenous tissue, microspore tetrad, pollen mother cell, male gametes
Solution: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.
What is meant by monosporic development of female gametophyte?
Solution: 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.
With a neat diagram, explain the 7-celled, 8 nucleate nature of female gametophyte.
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.
What are chasmogamous flowers? Can cross-pollination occur in cleistogamous flowers? Give reasons for your answer.
Solution: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.
Mention two strategies evolved to prevent self-pollination in flowers.
Solution: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.
What is self-incompatibility? Why does self-pollination not lead to seed formation in self-incompatible species?
Solution: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.
What is bagging technique? How is it helpful in a plant breeding programme?
Solution: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.
What is triple fusion? Where and how does it take place? Name the nuclei involved in triple fusion.
Solution: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
Why do you think zygote is dormant for sometime in a fertilized ovule?
Solution: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.
- Epicotyl and hypocotyl
- Coleoptile and coleorrhiza
- Integument and testa
- Perisperm and pericarp
- Epicotyl and hypocotyl
Epicotyl Hypocotyl Region of embryo above the cotyledon. Region of the embryo below the cotyledon. Terminates at the plumule. Terminates at the coteladonary node. Starts from coteladonary node. Starts from the radicle. Develops into upper part of the stem. Develops into that part of the stem that develops into roots. Elongates in epigeal germination. Elongates in hypogeal germination.
- Coleoptile and coleorrhiza
Coleoptile Coleorrhiza It is a protective sheath. It is an undifferentiated sheath. Protects young shoot tip in cereals and grass. Protects the roots of a germinating grass or cereal. Comes out of the soil. Remains inside the soil. Covers the plumule. Covers the root cap and radical. Breaks the seed coat and grows. Breaks the seed coat and stops growth.
- Integument and testa
Integument Testa Covers the ovule. Outer covering of seed. The cells are living. The cells are dead. Pre-fertilized structure. Post fertilized structure. Sclereids are absent. Sclereids are present. One or two layered. One layered.
- Perisperm and pericarp
Perisperm Pericarp Part of a seed. Part of a fruit. Usually dry. Dry or fleshy. Present in only a few seeds. Found in all the fruits. Non-functional in seed. Protects the fruit and helps in nutrition and dispersal.
Why is apple called a false fruit? Which part of the flower forms the fruit?
Solution: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.
- What is meant by emasculation? When and why does a plant breeder employ this technique?Solution: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.
If one can induce parthenocarpy through the application of growth substances, which fruits would you select to induce parthenocarpy and why?
Solution: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.
Explain the role of tapetum in the formation of pollen grain wall.
Solution: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.
What is apomixis and what is its importance?
Solution: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.
NCERT Solutions for Class 12 Biology Chapter 2 Sexual Reproduction in Flowering Plants
Sexual reproduction in flowering plants explains the process of formation of male and female gametes in plants and how they are involved in the production of new plant varieties. The process of pollination, pre-fertilization events, fusion of male and female gametes, and the post-fertilization events and structure are elaborated here. NCERT Solutions Biology Class 12 helps the students to understand the concepts thoroughly and in great detail.
The process of microsporogenesis can be defined as the formation of microspore from the PMC and occurs through meiosis. The pollen grains that denote the male gametophyte possess a hard outer layer wall known as the exine and the inner wall known as the inline. The pollen grains that have matured consist of the generative cells and a vegetative cell.
The chapter provides details about various parts of a flowering plant, right from the process of formation up till the reproduction finally. The transfer of pollen grains to the stigma of a pistil is termed as pollination. Pollination is explained in detail in the chapter, along with a clear demonstration of different types of pollination, agents of pollination and so on.
Some Important concepts mentioned in the chapter are given below:
- Pre-fertilization-Structure and Events
- Double fertilization
- Apomixis and Polyembryony
Key Features of NCERT Solutions Class 12 Biology Chapter 2 Sexual Reproduction in Flowering Plants
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- It enhances the conceptual knowledge of the students.
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- Use of a labelled diagram wherever necessary.
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