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Class 12 Biology NCERT Solution CH-2

NCERT Solutions for Claass 12 Biology of all chapters is available here. CBSE Students can view these solutions for free here. NCERT solutions of Biology is very important for all the students for there board examinations as well as NEET examination 2022. Each and every students of class 12 who opted Biology must go through these solutions.

In this section we have uploaded the NCERT Solution For class 12 Biology CH-2 Sexual reproduction in Plants.

Sexual Reproduction In Flowering Plants NCERT Solution

1. Name the parts of anangiosperm flower in which development of male and female gametophytes take place.
Ans: Development of male gametophyte (micro- gametogenesis) occurs in pollen sac of anther up to 2 – celled stage. The female gametophyte develops (megagametogenesis) in the nucellus of 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-

MicrosporogenesisMegasporogenesis
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.

 

3. Arrange the following terms in the correct development sequence: Pollen grain, sporogenous tissue, microspore tetrad, pollen mother cell, male gametes.
Ans: The correct developmental sequence for the formation of male gametes is :
Sporogenous tissue —» Pollen mother cell —» Microspore tetrad —» Pollen grain —» Male gametes.

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

Ans- Refer to NCERT book.

5. What is meant by monosporic development of female gametophyte?
Ans: In most of flowering plants one of the megaspores is functional whereas the other three degenerate. And Only the functional megaspore develops into the female gametophyte or embryo sac. This process of development of embryo sac from a single megaspore is called monosporic development.

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

Ans- Refer NCERT book.

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

Ans- 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.

Ans- Two Strategies to prevent self pollinaztion are-

  • 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-incompatiblility? Why does self-pollination not lead to seed formation in self-incompatible species?

Ans- Incompatibility- The inability of certain functional male and female gametes, even from genetically similar plant species, to fuse with each other and produce viable seeds is called self-incompatibility.

Self-pollination does not lead to seed formation in self-incompatible species because of the interaction of the chemical substances produced by the male gametophyte and the tissue of the style which obstruct fertilisation (pollen–pistil interaction). The chemicals inhibit the germination of pollen grains and the further growth of the pollen tube so as to avoid inbreeding and to help outbreeding.

 

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

Ans- It is the covering of emasculated flowers (removal of anthers in bud condition from a bisexual flower by a bag of butter paper or polythene in their bud condition i.e., before anthesis) to prevent contamination of its stigmas with unwanted pollens.

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

Ans-  when a male gamete fuses with two polar nuclei within the embryo sac of flowering plants, it is called Triple fusion.

The following events takes place during this process:-

  • 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 the zygote is dormant for sometime in a fertiUsed ovule?
Ans: The zygote after a period of rest develops into embryo. Most zygotes remain dormant till certain amount of endosperm forms. They do so, to provide assured nutrition to the developing embryo.

13. Differentiate between:

(a) Epicotyle and Hypocotyle

EpicotylHypocotyl
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.

(b) Coleoptile and coleorrihza

Coleoptile 

Coleorhiza 

• It is a conical protective sheath over the epicotyl bearing the shoot apex and leaf primordia.

• It is a protective sheath over the radicle and root cap.

• It has a terminal pore for the emergence of the first leaf.

• It is a solid structure.

• It comes out of the soil.

• It remains inside the soil.

• It protects the plumule during its emergence from the soil.

• It does not protect the radicle during its passage into the soil.

• It grows much beyond the grain.

• It stops growing after its emergence from the grain.

• It emerges from the soil, turns green in colour and carries out photosynthesis.

• It remains inside the soil and is non-green.

(c) integument and testa;

• It is the protective covering of the ovule.

• It is the protective covering of the seed.

• It is a thin covering.

• It is a thick covering.

• The cells are living.

• The cells are dead.

• Sclereids are absent in the cells.

• Sclereids are present in abundance in the cells.

• It arises from the chalazal end of the ovule.

• It is derived from the outer integument of the ovule.

• It is a pre-fertilisation structure.

• It is a post-fertilisation structure.

 

(d)Perisperm and pericarp

PerispermPericarp
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.

14.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.

15. What is meant by emasculation? When and why does a plant breeder employ this technique?
Ans: Removal of stamens or anthers of a bisexual flower without affecting the female reproductive organs is called emasculation. This technique is used in artificial hybridisation. In such crossing experiments it is important to make sure that only the desired pollen grains are used for pollination and the stigma is protected from contamination from unwanted pollens. This is achieved by emasculation and bagging technique. This technique is used to obtain desired variety of seeds.

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 of units 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.
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.

  1. 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.

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