Chapter 2: Sexual Reproduction in Flowering Plants

Q1. What is double fertilization? Why is it significant?

Solution

Double fertilization involves two events: (1) One male gamete fuses with egg to form zygote (syngamy), (2) Other male gamete fuses with two polar nuclei to form Primary Endosperm Nucleus (PEN).

Significance: Ensures food supply for developing embryo through endosperm formation.

Q2. Distinguish between perfect and imperfect flowers.

Solution

Perfect: Both stamens and carpels present (e.g., Hibiscus, Mustard)
Imperfect: Either stamens or carpels absent (e.g., Corn, Papaya)

Q3. What are the three types of pollination based on source of pollen?

Solution

1. Self-pollination: Pollen from same flower or plant
2. Cross-pollination: Pollen from different plant of same species
3. Geitonogamy: Pollen from different flower on same plant

Q4. What is the structure of an ovule? Name its parts.

Solution

Parts of ovule: (1) Funicle (stalk) (2) Hilum (attachment point) (3) Integuments (protective layers) (4) Nucellus (nutritive tissue) (5) Embryo sac (female gametophyte) containing egg cell, synergids, polar nuclei, antipodals

Q5. What are the effects of emasculation and bagging in plant breeding?

Solution

Emasculation: Removal of anthers from bisexual flowers before they mature, to prevent self-pollination.

Bagging: Covering emasculated flowers with bags to prevent unwanted pollen from reaching the stigma.

Q6. Explain microsporogenesis. Where does it occur?

Solution

Microsporogenesis is the formation of microspores (pollen grains) from the microspore mother cell (MMC) inside the anther.

Process: (1) MMC undergoes meiotic division (2) Tetrads of microspores are formed (3) Microspores separate and develop into pollen grains (male gametophytes)

Q7. What is megasporogenesis? Describe the development of the embryo sac.

Solution

Megasporogenesis is the formation of megaspores from the megaspore mother cell (MMC) inside the ovule.

Process: (1) MMC undergoes meiosis to form 4 megaspores (2) Three degenerate, one remains functional (3) Functional megaspore undergoes 3 mitotic divisions to form 8-nucleate, 7-celled embryo sac (4) Contains: 1 egg cell + 2 synergids + 3 antipodals + 2 polar nuclei

Q8. What is pollen-pistil interaction?

Solution

Pollen-pistil interaction involves all events from pollen deposition on stigma to the entry of pollen tube into the ovule.

Compatibility check: (1) Pollen lands on stigma (2) Stigma recognizes compatible pollen using chemical signals (3) Compatible pollen germinates and forms pollen tube (4) Incompatible pollen is rejected

Q9. What is apomixis? How is it different from parthenocarpy?

Solution

Apomixis: Seeds formed without fusion of gametes (e.g., Asteraceae, Grasses)
Parthenocarpy: Fruit formation without fertilization, no seed formation (e.g., Banana, Grapes)

Q10. What is polyembryony? How is it useful in agriculture?

Solution

Polyembryony is the occurrence of more than one embryo in a seed.

Agricultural use: (1) Produces disease-free plants (2) Uniform genetic material (3) Faster propagation (4) Citrus fruits commonly show polyembryony

Q11. Describe the process of endosperm development in angiosperms.

Solution

Nuclear endosperm: Free nuclear divisions before cell wall formation (e.g., Coconut)
Cellular endosperm: Cell wall formation concurrent with nuclear divisions (e.g., Solanaceae)

Q12. What are the agents of pollination? Give two examples each.

Solution

Abiotic: Wind (Maize, Grasses), Water (Vallisneria, Hydrilla)
Biotic: Insects (Hibiscus, Lotus), Birds (Bottlebrush, Bignonia), Bats (Kigelia)

Q13. Describe embryo development after fertilization.

Solution

Process: (1) Zygote divides to form basal cell and terminal cell (2) Basal cell forms suspensor (3) Terminal cell forms embryo (4) Embryo develops plumule, cotyledons, radicle, and hypocotyl

Q14. What are the advantages of cross-pollination over self-pollination?

Solution

1. Produces genetically diverse offspring
2. Increases adaptability to changing environments
3. Produces vigorous hybrid offspring
4. Eliminates harmful recessive traits
5. Promotes evolution

Q15. What is the significance of seed formation in angiosperms?

Solution

1. Protects the embryo
2. Provides food for developing embryo
3. Aids in dispersal to new habitats
4. Seeds remain dormant until favourable conditions
5. Ensures survival of the next generation

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