Chapter 11: Reproduction: How Life ContinuesClass 9 Science — summary, notes, extra questions & NCERT solutions

Summary

This chapter explains how organisms produce new individuals so that life continues across generations. Reproduction is of two broad types. In asexual reproduction a single parent produces offspring that are almost exact copies (clones), with no mixing of characters; its methods include binary fission (amoeba, bacteria), budding (yeast, hydra), fragmentation (spirogyra), regeneration (planaria), spore formation (mould, ferns) and vegetative propagation in plants (by roots, stems, leaves — as in potato eyes and Bryophyllum leaves — and artificially by cuttings, layering and grafting). Asexual reproduction is fast and useful when conditions are stable, and farmers use it to keep desirable plant varieties unchanged. In sexual reproduction two parents contribute specialised sex cells called gametes; their fusion (fertilisation) forms a zygote that develops into the offspring, which inherits a mix of both parents’ characters — this variation helps populations adapt and survive change. In flowering plants the flower is the reproductive organ: pollen (male) reaches the stigma, the pollen tube carries male gametes to the ovule for fertilisation, and the ovary becomes the fruit while ovules become seeds. In humans, the male and female reproductive systems produce sperm and eggs; at puberty hormonal changes make these systems mature, the menstrual cycle prepares the female body for pregnancy, fertilisation forms a zygote that develops in the uterus, and the chapter also notes reproductive health.

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