NCERT Solutions for Class 12 Biology Chapter 1 Sexual Reproduction

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

Ans: Male gametophyte develops in anther (pollen sac / microsporangium). Female gametophyte develops in ovule (inside ovary).

2) Q. Arrange the following terms in the correct development sequence: Pollen grain, sporogenous tissue, microspore tetrad, pollen mother cell, male gametes.

Ans: Sporogenous tissue → Pollen mother cell → Microspore tetrad → Pollen grain → Male gametes

3) Q. With a neat, labelled diagram, describe the parts of a typical angiosperm ovule.

Ans: Main parts: funicle, hilum, integuments, micropyle, nucellus, embryo sac, chalaza.

4) Q. What is meant by monosporic development of female gametophyte?

Ans: When the embryo sac (female gametophyte) develops from one functional megaspore out of the four megaspores formed.

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

Ans: Embryo sac has 7 cells but 8 nuclei:
3 antipodals (chalazal end) + 2 synergids and 1 egg (micropylar end) + 1 central cell with 2 polar nuclei.

6) Q. What are chasmogamous flowers? Can cross-pollination occur in cleistogamous flowers? Give reasons.

Ans: Chasmogamous flowers are open and exposed (can be cross-pollinated).
Cleistogamous flowers remain closed, so cross-pollination generally cannot occur; they ensure self-pollination.

7) Q. Mention two strategies evolved to prevent self-pollination in flowers.

Ans: Any two: Dichogamy (anther and stigma mature at different times), Herkogamy (physical separation of anther and stigma), Self-incompatibility.

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

Ans: Self-incompatibility is a genetic mechanism where a plant rejects its own pollen.
So pollen fails to germinate / pollen tube growth is blocked → no fertilisation → no seed.

9) Q. What is bagging technique? How is it useful in a plant breeding programme?

Ans: Covering a bisexual flower (usually after emasculation) with a bag to prevent unwanted pollen.
Useful to ensure controlled cross-pollination with desired pollen only.

10) Q. What is triple fusion? Where and how does it take place? Name the nuclei involved.

Ans: Fusion of one male gamete with two polar nuclei (or secondary nucleus) in the central cell of embryo sac.
It forms the primary endosperm nucleus (3n).
Nuclei: male nucleus + two polar nuclei.

11) Q. Why do you think the zygote is dormant for sometime in a fertilized ovule?

Ans: Zygote stays dormant until the endosperm develops and provides nourishment; then embryo development starts.

12) Q. Differentiate between: (a) hypocotyl and epicotyl; (b) coleoptile and coleorhiza; (c) integument and testa; (d) perisperm and pericarp.

Ans:
(a) Hypocotyl: embryonic axis below cotyledons → forms root region. | Epicotyl: above cotyledons → forms shoot region.
(b) Coleoptile: sheath covering plumule (shoot) in monocots. | Coleorhiza: sheath covering radicle (root) in monocots.
(c) Integument: ovule covering (before fertilisation). | Testa: seed coat formed from integument (after fertilisation).
(d) Perisperm: persistent nucellus in seed (nutritive). | Pericarp: fruit wall formed from ovary wall.

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

Ans: Apple is a false fruit because edible part develops from thalamus (receptacle) along with ovary.
True fruit forms from ovary; in apple, major fleshy part is thalamus.

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

Ans: Removing anthers from a bisexual flower before pollen release.
Used in hybridisation to prevent self-pollination and allow controlled cross-pollination.

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

Ans: Choose fruits where seedless variety is preferred, e.g., watermelon, grapes, orange.
Because parthenocarpy produces seedless fruits with better consumer preference.

16) Q. Explain the role of tapetum in the formation of pollen-grain wall.

Ans: Tapetum provides nourishment and supplies materials for pollen wall formation, especially sporopollenin for the exine.

17) Q. What is apomixis and what is its importance?

Ans: Seed formation without fertilisation.
Importance: produces genetically identical offspring, preserves hybrid traits, helps fix desirable characters.

18) Q. Differentiate between microsporogenesis and megasporogenesis. Which division occurs? What structures are formed?

Ans:
Microsporogenesis: in anther; pollen mother cell → (meiosis) → microspore tetrad → pollen grains.
Megasporogenesis: in ovule; megaspore mother cell → (meiosis) → megaspores (one functional) → embryo sac.