Chapter 11 — Reproduction — How Life Continues

Chapter 11 of the Class 9 Science NCERT textbook, "Reproduction", covers the biological process by which living organisms produce new individuals, exploring asexual reproduction (vegetative propagation, budding, spore formation) and sexual reproduction in plants, animals, and humans.

• Why Organisms Reproduce — Reproduction is the biological process by which living beings produce new individuals of their own kind, ensuring life continues on Earth, and occurs in two main forms, asexual and sexual.
• Asexual vs Sexual — Asexual reproduction uses one parent and mitosis to make identical clones through vegetative propagation, budding, or spores. Sexual reproduction uses two parents and meiosis, mixing chromosomes to create genetic variation.
• Reproduction in Plants and Animals — Flowering plants reproduce through pollination and fertilisation between stamen and pistil. Animals use external fertilisation (many eggs, low survival) or internal fertilisation (fewer eggs, higher survival).
• Human Reproduction — In humans, an egg released monthly may be fertilised in the oviduct, implant, and develop over about nine months, or shed as menstruation. Contraceptive methods space births, and condoms also prevent STIs.

1. 01Asexual reproduction involves one parent and produces genetically identical clones via mitosis; methods include vegetative propagation (cutting, grafting, layering, tissue culture), budding in hydra, and spore formation in fungi.
2. 02Sexual reproduction involves two parents; meiosis halves the chromosome number to form gametes (sperm and eggs), and the random mixing of chromosomes during meiosis creates genetic variation among offspring.
3. 03In flowering plants, the stamen (male) produces pollen grains and the pistil (female) contains the ovary with ovules; pollination transfers pollen from anther to stigma via wind, water, insects, or birds, after which fertilisation forms a zygote that develops into a seed inside the fruit.
4. 04In animals, external fertilisation occurs outside the body (fish, frogs) producing many eggs with low survival rates, while internal fertilisation occurs inside the female (reptiles, birds, mammals) with fewer eggs and higher survival rates.
5. 05In humans, one mature egg is released monthly from the ovaries (ovulation); if fertilised by sperm in the oviduct, a zygote forms, implants in the uterus, and pregnancy of about nine months begins divided into three trimesters; if unfertilised, the uterine lining sheds as menstruation.
6. 06Contraceptive methods include barrier methods (condoms), oral pills that alter hormone levels, intra-uterine devices (Copper-T), and surgical methods; condoms also prevent sexually transmitted infections (STIs) such as HIV, gonorrhoea, and syphilis.