Ch 8 covers reproduction — the biological process that ensures continuation of species. Students learn about asexual reproduction (fission, budding, fragmentation) and sexual reproduction in plants and humans.
Single parent, offspring are clones. Binary fission: Amoeba (splits in two). Multiple fission: Plasmodium (many cells). Budding: Hydra (outgrowth becomes new organism). Fragmentation: Spirogyra (breaks into pieces). Regeneration: Planaria (piece grows into complete organism). Vegetative propagation: runners (strawberry), tubers (potato), leaves (Bryophyllum).
Flower parts: sepals, petals, stamens (male: anther + filament), pistil (female: stigma + style + ovary). Pollination: transfer of pollen from anther to stigma (self/cross). Fertilisation: pollen tube grows to ovule, male gamete fuses with egg cell. Ovule → seed, ovary → fruit. Germination: seed grows into new plant.
Male: testes produce sperm + testosterone. Female: ovaries produce eggs + estrogen/progesterone. Menstrual cycle: ~28 days. Fertilisation: sperm + egg in fallopian tube → zygote → embryo implants in uterus → placenta nourishes foetus. Contraception: barrier (condom), chemical (pills), surgical (vasectomy, tubectomy), copper-T (IUD).
Download: https://ncert.nic.in/textbook/pdf/jesc108.pdf | Complete book: https://ncert.nic.in/textbook/pdf/jesc1ps.zip
Sexual reproduction creates variation through combination of DNA from two parents. Variation helps a species survive changing environments — some individuals may be better adapted to new conditions. Without variation (asexual reproduction), a single environmental change could wipe out the entire population.
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