1. Importance of DNA Copying
Reproduction at its core involves the replication of chromosomes in the cell nucleus via **DNA copying**. This process ensures that body designs are faithfully handed down across generations while introducing minor variations that drive **evolution**.
2. Modes of Asexual Reproduction
- Fission: Unicellular organisms split into new individuals (e.g., **Binary Fission** in Amoeba, **Multiple Fission** in Plasmodium).
- Budding: A small outgrowth or bud develops on the parent body, matures, and detaches (e.g., Hydra, Yeast).
- Regeneration: Broken or cut body fragments can grow into complete new organisms if severed (e.g., Planaria).
- Vegetative Propagation: New plants grow from vegetative parts like roots, stems, or leaves (e.g., Bryophyllum leaves developing plantlets along margins).
3. Sexual Reproduction in Flowering Plants
Flowers house the reproductive machinery of angiosperms:
- Stamen (Male part): Consists of the anther and filament. Produces sticky male gametes called **pollen grains**.
- Carpel/Pistil (Female part): Located centrally, containing the stigma, style, and ovary. The ovary houses ovules containing female egg cells.
- Pollination & Fertilization: Transfer of pollen from the anther to a receptive stigma. Once docked, a pollen tube bores down the style to deliver the male cell to the ovule, forming a **zygote**.
4. Human Reproductive Health & Contraception
Methods used to prevent unwanted pregnancies and regulate family health:
- Mechanical Barriers: Condoms block entry of sperm; protect against Sexually Transmitted Diseases (STDs) like HIV-AIDS.
- Chemical Methods: Oral pills alter hormonal balances to stop egg release from ovaries.
- Surgical Methods: **Vasectomy** (blocking the vas deferens in males) or **Tubectomy** (blocking fallopian tubes in females) to permanently halt gamete transit.
CBSE Board Exam Core Focus
What happens when the egg is not fertilized? If the ovulated egg is not fertilized by a sperm, it lives for about one day. The thick, spongy lining of the uterus—which had built up with blood vessels to support a prospective embryo—is no longer needed. This lining slowly breaks down and sheds out of the vagina as blood and mucous, a monthly process called **Menstruation**.