How Do Organisms Reproduce?
Reproduction is not essential for the survival of an individual, but it is absolutely essential for the survival of a species. Without it, life on Earth would eventually disappear.
In this chapter, we will explore the two major highways of life: Asexual Reproduction (The Clone Wars) and Sexual Reproduction (Variation & Evolution).
Part 1: Asexual Reproduction
This method involves a single parent. No gametes are involved, and the offspring are genetically identical (clones) to the parent.
Modes of Asexual Reproduction:
- Fission: The parent cell divides into daughter cells.
- Binary Fission: Splits into two (e.g., Amoeba, Leishmania).
- Multiple Fission: Splits into many (e.g., Plasmodium).
- Fragmentation: The body breaks into pieces, and each piece grows into a new organism (e.g., Spirogyra).
- Regeneration: If cut into pieces, specialized cells re-grow the missing parts (e.g., Planaria, Hydra).
- Budding: A small outgrowth (bud) forms on the parent, grows, and detaches (e.g., Hydra, Yeast).
- Vegetative Propagation: New plants grow from roots, stems, or leaves (e.g., Potato eyes, Bryophyllum leaf buds, Rose cuttings).
- Spore Formation: The parent produces hundreds of microscopic reproductive units called spores (e.g., Rhizopus/Bread Mould).
Part 2: Sexual Reproduction in Plants
Sexual reproduction requires two parents and the fusion of male and female gametes (germ cells). This creates variation, which is the basis of evolution.
1. The Flower: The Reproductive Unit
A typical flower has four main parts:
- Sepals & Petals: Protective and attractive parts.
- Stamen (Male): Consists of Anther (produces Pollen Grains) and Filament.
- Pistil/Carpel (Female): Consists of Stigma (sticky top), Style (tube), and Ovary (contains Ovules/Eggs).
2. Pollination & Fertilization
- Pollination: Transfer of pollen from Anther to Stigma. Can be Self-pollination (same flower) or Cross-pollination (different flower).
- Fertilization: The male gamete travels down the pollen tube and fuses with the female gamete in the ovary.
- Result: Ovule becomes Seed. Ovary becomes Fruit.
Part 3: Human Reproduction
Humans use sexual reproduction. This process begins at Puberty, a period of rapid growth and sexual maturity.
1. Male Reproductive System
- Testes: Produce Sperm (male gamete) and Testosterone (hormone). Located outside the body in the Scrotum to maintain a lower temperature.
- Vas Deferens: The tube that carries sperm.
- Urethra: Common passage for both sperm and urine.
2. Female Reproductive System
- Ovaries: Produce Eggs (Ova) and hormones (Estrogen/Progesterone).
- Fallopian Tube (Oviduct): The site where Fertilization takes place.
- Uterus (Womb): Where the baby develops.
3. What happens if the egg is NOT fertilized?
The lining of the uterus, which thickened to receive a baby, breaks down. It exits the vagina as blood and mucus. This monthly cycle is called Menstruation.
Part 4: Reproductive Health
Reproductive health involves safe sexual practices and family planning.
Contraception Methods (Birth Control)
| Method | Description | Examples |
|---|---|---|
| Mechanical Barrier | Prevents sperm from meeting egg physically. | Diaphragms. (Also prevents STDs like HIV/AIDS). |
| Chemical | Changes hormonal balance to prevent egg release. | Oral Pills. |
| IUCD | Device placed in uterus to prevent pregnancy. | Copper-T. |
| Surgical | Blocks gamete transport permanently. | Vasectomy (Males), Tubectomy (Females). |
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