Class 12 Biology - Chapter 1 Notes
Chapter 1: Sexual Reproduction in Flowering Plants
1. Flower - A Reproductive Unit:
- Flower has 4 whorls: Calyx, Corolla, Androecium (male), Gynoecium (female).
- Androecium: stamens = anther + filament.
- Gynoecium: pistil = stigma + style + ovary.
2. Pre-Fertilization Events:
a. Gametogenesis:
- Microsporogenesis: anther - microspores (pollen).
- Megasporogenesis: ovule - megaspore.
b. Male Reproductive Structure:
- Anther has 2 lobes, each with 2 pollen sacs.
- Microspore mother cells undergo meiosis to form microspores.
- Pollen grain: Exine (outer) + Intine (inner), with vegetative and generative cells.
c. Female Reproductive Structure:
- Ovule has nucellus, integuments, and embryo sac.
- Embryo sac: 7 cells, 8 nuclei - egg, synergids, antipodals, central cell with 2 polar nuclei.
3. Pollination:
- Types: Autogamy (same flower), Geitonogamy (same plant), Xenogamy (different plant).
- Agents: Wind, water, insects.
- Pollen germinates on stigma - pollen tube - ovule via micropyle.
4. Fertilization (Double Fertilization):
- 1 sperm + egg - zygote (syngamy).
- 1 sperm + 2 polar nuclei - endosperm (triple fusion).
- Unique to angiosperms.
Chapter 1: Sexual Reproduction in Flowering Plants
1. Flower - A Reproductive Unit:
- Flower has 4 whorls: Calyx, Corolla, Androecium (male), Gynoecium (female).
- Androecium: stamens = anther + filament.
- Gynoecium: pistil = stigma + style + ovary.
2. Pre-Fertilization Events:
a. Gametogenesis:
- Microsporogenesis: anther - microspores (pollen).
- Megasporogenesis: ovule - megaspore.
b. Male Reproductive Structure:
- Anther has 2 lobes, each with 2 pollen sacs.
- Microspore mother cells undergo meiosis to form microspores.
- Pollen grain: Exine (outer) + Intine (inner), with vegetative and generative cells.
c. Female Reproductive Structure:
- Ovule has nucellus, integuments, and embryo sac.
- Embryo sac: 7 cells, 8 nuclei - egg, synergids, antipodals, central cell with 2 polar nuclei.
3. Pollination:
- Types: Autogamy (same flower), Geitonogamy (same plant), Xenogamy (different plant).
- Agents: Wind, water, insects.
- Pollen germinates on stigma - pollen tube - ovule via micropyle.
4. Fertilization (Double Fertilization):
- 1 sperm + egg - zygote (syngamy).
- 1 sperm + 2 polar nuclei - endosperm (triple fusion).
- Unique to angiosperms.
