NCERT Solutions for Class 12 Biology Chapter 2: Sexual Reproduction in Flowering Plants
1. Name the parts of an angiosperm flower in which development of male and female gametophyte take place.
Ans. In an angiosperm flower:
Male gametophyte know as pollen grain, develops inside the chamber of anther.
Female gametophyte is known as embryo sac, develops inside the nucellus of the ovule.
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 involves the formation of microspores from microspore mother cells by division and it occurs inside the pollen sac of anther while megasporogenesis is the arrangement of magaspores from magaspore mother cell and it occurs in the ovule of ovary.
In both microsporogenesis and megasporogenesis meiosis or reductional cell division occurs which results in generation of haploid gametes.
Haploid microspore or pollen green (male gametophyte) are formed at the end of microsporogenesis.
Haploid microspores or embryo sac (female gametophyte) are formed at the end of megasporogenesis.
3. Arrange the following terms in the correct developmental sequence: Pollen grain, sporogenous tissue, microspore tetrad, pollen mother cell, male gametes.
Ans. The correct development sequence for the formation of male gametes is:
Sporogenous tissue → Pollen mother cell → Microspore tetrad → Pollen gain → male gametes.
4. With a neat, labelled diagram, describe the parts of a typical angiosperm ovule.
The various parts of an ovule are:
(i) Funile: It is stalk like structure that serves as the point of attachment of the ovule to the placenta of ovary.
(ii) Hilum: It is the point where funicle attached to the ovule body.
(iii) Integument: Covering layer that protects the developing embryo.
(iv) Microphyls: The path where the pollen tube enters the ovules during fertilization.
(v) Nucellus: A mass of cells that lies enclosed within the integuments cells of nucellus have abundant reserves of food.
(vi) Chalazal: It is based swollen parts of the nucellus from where the integuments originate.
5. What is meant by monosporic development of female gametophyte?
Ans. In majority of flowering plants one of the megaspores is functional while the other three degenerate. The formation of female gametophyte from single functional megaspore is known as monocarpic development.
6. With a neat diagram explain the 7-celled, 8-nucleate nature of the female gametophyte.
Embry o sac (or female gametophyte) is formed by three successive mitotic divisions that take place in the nucleus of megaspore.
The nucleus of the functional megaspore divides meiotically to form two nuclei which move to the opposite poles, forming the 2-nucleate embryo sac. Two more sequential mitotic nuclear division result in the formation of the 4-nucleate and later the 8-nucleate stages of the embryo sac. After the 8-nucleate stage, cell walls are laid down leading to the organisation of the typical female gametophyte or embryo sac. Six of the eight nuclei are grouped together at micropylar and chalazal end and form the egg apparatus and antipodals respectively. The large central cell left over with two polar nuclei. Thus, a typical female gametophyte consists of 7 cell with 8 nucleus.
7. What are chasmogamous flowers? Can cross-pollination occur in cleistogamous flowers? Give reasons for your answer.
Ans. Chasmogamous flowers are those flowers which are open with exposed anther and stigma.
Cross pollination cannot occur in cleistogamous flowers as they do not open at all. So, their anthers and stigma remain inaccessible. However they do produce seed through self-pollination.
8. Mention two strategies evolved to prevents self-pollination in flowers.
Ans. The two strategies involved in preventing self-pollination in flowers are:
(i) Dichogamy: Maturation of anther and stigma at different times in a bisexual flower prevent self-pollination.
(ii) Self-sterility (or self-incompatibility): Due to the presence of self-sterile gene in some flowers, pollen grains do not germinate on the stigma of that flowers.
9. What is self-incompatibility? Why does self-pollination not lead to seed formation in self-incompatible species?
Ans. Self incompatibility: It is the condition which prevents the pollen of the flower to associate with the stigma of the same flower and fertilise the female gametes.
Self pollination cannot lead to the formation of seeds in a self-incompatible species. This is because self-incompatibility lead to the inability to produce zygote that would develop into an embryo and hence form seeds.
10. What is bagging technique? How is it useful in a plant breeding programme?
Ans. Bagging technique: It is technique of preventing contamination from pollen grain during breeding by covering the flower with butter paper or polythene bag.
Uses of Bagging technique in plant breeding programme:
(i) Prevents contamination with foreign pollen.
(ii) Prevents damages by animals.
(iii) Prevents germination of unwanted pollen on stigma.
11. What is triple fusion? Where and how does it take place? Name the nuclei involved in triple fusion.
Ans. Triple fusion: It refers to the process of fusion of three haploid nucleic i.e., one male gamete nucleic with two nucleic.
It takes place in embry
o sac. It this one male gamete fuses with two polar nuclei to produce a triploid primary endosperm nucleus.
1 male nuclei and 2 polar nuclei involved in triple fusion.
12. Why do you think the zygote is dormant for sometime in fertilised ovule?
Ans. Zygote is dormant for sometime in fertiliser ovule because the embryo develops only after formation of endosperm. So, the zygote waits for endosperm formation which provides nutrition to the developing embryo.
13. Differentiate between:
(a) Hypocotyl and Epicotyl.
(b) Coleoptile and Coleorrhiza
(c) Integument and Testa
(d) Perisperm and Pericarp.
Ans. Differences between Hypocotyl and Epicotyl
||It is the part of embryonal axis in between plumule and cotyledon node.|
||In hypogeal germination, epicotyl elongates so that cotyledons remain in the soil.|
||It terminate with the plumule.|
Differences between Coleoptile and Coleorhiza
||The radical and root cap are enclosed in a sheath called coleorrhiza.|
||Coleorrhiza is a solid structure.|
||It does not protect the radicle during its passage into the soil.|
||After emergence from grain in stops growing.|
||Coleorhiza does not come out of soil. It remain’s non-green.|
Differences between Integument and Testa
||It is outer covering of seed.|
||Its is quite thick and single layered.|
||It cells are dead.|
||Cells are rich in sclereids.|
||It is derived from outer integument of ovule after fertilization.|
||It is a post fertilized structure.|
Differences between Integument and Testa
||It is the covering of fruit that develops from ovary wall.|
||It is a part of fruit.|
||It is dry of fleshy|
||It is protective covering and also helps in dispersal and nutrition.|
||It is found in all fruits.|
14. Why is apple called a false fruit? Which part(s) of the flower forms the fruit?
Ans. True fruits: Fruits that develop from ovary is called true fruits.
False fruits: Fruits that develop any other part of flower except ovary, is called false fruits.
Apple is called false fruit because it develops from thalmus of the flower.
Usually ovary forms the fruit after fertilization or without fertilization in parthenocarpic fruits.
15. What is meant by emasculation? When and why does a plant breeder employ this technique?
Ans. The process of removal of stamens or anthers of a bisexual flower without affecting the female reproductive organs is called emasculation. Plant breeder employs this technique to prevent self pollination. This is useful in artificial hybridization where the desired pollen is require.
16. If one can induce parthenocarpy through the application of growth substances, which fruits would you select to induce parthenocarpy and why?
Ans. Parthenocarpic fruits are seedless. They develop from ovary without fertilization. Banana, grapes, oranges, Pineapple, Guava, Watermelon, lemon are selected because these seedless and are of high economic importance. The fruits in which seeds or seed part form edible portion (e.g., Pomegranate) are not selected to induce parthenocarpy.
17. Explain the role of tapetum in the formation of pollen grain wall.
Ans. Tapetum is the innermost layer of micro sporangium. It produces the exine layer is pollen grains, which is composed of sporopollenin, the most resistant fatty substance. During microsporogenesis, the cells of tapetum produce various enzymes, hormones, amino acids and other nutritions material required for the development of pollen grain.
18. What is apomixis and what is its importance?
Ans. Apomixis is a mode of asexual reproduction that produces seeds without fertilization, e.g., some species of Asteraceae and Grasses.
(i) It is cost effective method of producing seeds.
(ii) It has great use for plant breeding when specific traits of a plant have to be preserved.
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