Sexual Reproduction in Flowering Plants – Class 12 Biology notes, important questions and MCQs

Chapter overview

Flowers carry the reproductive organs. Pollen from the anther reaches the stigma (pollination), the male gametes fuse with the egg and polar nuclei (double fertilisation), and seeds and fruits develop.

Pre-fertilisation

• Stamen = anther + filament; microspore mother cells undergo meiosis to form pollen grains (male gametophyte).
• Pistil = stigma + style + ovary; the ovule's megaspore mother cell forms the embryo sac (7-celled, 8-nucleate).
• Pollination: self (autogamy, geitonogamy) or cross (xenogamy) by wind, water or animals.

Double fertilisation and after

• One male gamete + egg → zygote (2n); the other + two polar nuclei → primary endosperm nucleus (3n).
• Endosperm nourishes the embryo; ovule → seed, ovary → fruit.
• Apomixis forms seeds without fertilisation; parthenocarpy forms seedless fruits.

Key terms

Double fertilisation

syngamy plus triple fusion, unique to flowering plants

Apomixis

production of seeds without fertilisation

Exine

tough outer wall of pollen made of sporopollenin

Important questions with answers

Quick revision

• Triple fusion gives the 3n endosperm.
• Geitonogamy is genetically self-pollination.
• Sporopollenin is the most resistant organic material.

Exam tips

• Remember the embryo sac as 7 cells, 8 nuclei: egg apparatus (3), antipodals (3), central cell (2 polar nuclei).
• Learn the outbreeding devices: dichogamy (anther and stigma mature at different times), herkogamy, self-incompatibility, and unisexual flowers (dioecy).

Practice MCQs

1. The male gametophyte of a flowering plant is the

   1. ovule
   2. anther
   3. pollen grain
   4. stigma
   Show answer

   Answer: (c) pollen grain. Pollen grain.

2. Ovary develops into the

   1. fruit
   2. seed
   3. embryo
   4. endosperm
   Show answer

   Answer: (a) fruit. Fruit.

3. A typical embryo sac is

   1. 8-celled, 8-nucleate
   2. 7-celled, 8-nucleate
   3. 7-celled, 7-nucleate
   4. 8-celled, 7-nucleate
   Show answer

   Answer: (b) 7-celled, 8-nucleate. Central cell has two polar nuclei.

4. Pollination between flowers of the same plant is

   1. autogamy
   2. cleistogamy
   3. xenogamy
   4. geitonogamy
   Show answer

   Answer: (d) geitonogamy. Geitonogamy.

5. The part of the embryo sac that develops into the endosperm is the

   1. egg
   2. synergid
   3. central cell (polar nuclei)
   4. antipodal
   Show answer

   Answer: (c) central cell (polar nuclei). After triple fusion.

6. Ploidy of the primary endosperm nucleus is

   1. n
   2. 3n
   3. 2n
   4. 4n
   Show answer

   Answer: (b) 3n. Male gamete + two polar nuclei.

7. The exine of pollen is made of

   1. sporopollenin
   2. pectin
   3. cellulose
   4. lignin
   Show answer

   Answer: (a) sporopollenin. Highly resistant.

8. In a coconut, the white kernel and the water are

   1. cellular and free-nuclear endosperm
   2. cotyledons
   3. perisperm
   4. pericarp
   Show answer

   Answer: (a) cellular and free-nuclear endosperm. Coconut water is free-nuclear endosperm.