Chapter 7 — How do Organisms Reproduce?

Chapter 7 of the Class 10 Science NCERT textbook, "How do Organisms Reproduce?", explains how organisms reproduce using asexual methods (fission, budding, fragmentation, regeneration, vegetative propagation, spore formation) and sexual reproduction, covering flowering plants and the human reproductive system including puberty, fertilisation, and contraception.

• Why reproduction copies DNA — Reproduction fundamentally involves copying DNA and building new cellular apparatus. The copies are similar but not identical, and these small variations are what drive evolution and help species survive changing conditions.
• Asexual versus sexual reproduction — A single parent can reproduce asexually through fission, budding, fragmentation, regeneration, vegetative propagation, or spores. Sexual reproduction instead combines DNA from two parents via gametes, generating far greater variation.
• Reproduction in plants and humans — In flowering plants, pollination and fertilisation turn a zygote into a seed within a fruit. In humans, puberty prepares the reproductive systems, the placenta nourishes the embryo, and menstruation and contraception regulate the cycle.

1. 01DNA copying is the fundamental event in reproduction; copies are similar but not identical, producing variations that drive evolution.
2. 02Asexual reproduction modes include binary fission (Amoeba, bacteria), multiple fission (Plasmodium), budding (Hydra, yeast), fragmentation (Spirogyra), regeneration (Planaria), vegetative propagation (potato, Bryophyllum), and spore formation (Rhizopus).
3. 03In flowering plants, pollen transfers from stamen to stigma (pollination), followed by fertilisation in the ovary to form a zygote that develops into a seed inside a fruit.
4. 04Sperms are produced in the testes (located in the scrotum for lower temperature); eggs mature in the ovaries, with one released monthly through the fallopian tube to the uterus.
5. 05The placenta — a disc embedded in the uterine wall — supplies glucose and oxygen from the mother's blood to the developing embryo and removes waste products.
6. 06If the egg is not fertilised, the thickened uterine lining breaks down and is expelled as blood and mucus over roughly two to eight days — this is menstruation.