NCERT Science Class 10 - Chapter 7: How do Organisms Reproduce - Notes

Learning Objectives

Understand the importance of reproduction for species survival
Learn modes of asexual reproduction
Understand sexual reproduction in flowering plants
Study the human reproductive system
Learn about reproductive health and contraception

Key Concepts

Asexual Reproduction

Involves a single parent; offspring are genetically identical (clones). Types:

Fission: Binary fission (Amoeba splits into two); multiple fission (Plasmodium forms many daughter cells)
Budding: New organism grows as an outgrowth (bud) on parent. Example: Hydra, yeast.
Spore formation: Spores are covered by thick walls for protection. Example: Rhizopus (bread mould).
Regeneration: An organism re-grows from a broken part. Example: Planaria, Hydra.
Fragmentation: Organism breaks into pieces, each growing into a new individual. Example: Spirogyra.
Vegetative propagation: New plants from vegetative parts (roots, stems, leaves). Examples: tuber (potato), runner (strawberry), leaf buds (Bryophyllum).

Sexual Reproduction in Flowering Plants

Flower is the reproductive organ. Parts:

Stamen (male): Anther (produces pollen grains) + Filament
Pistil/Carpel (female): Stigma (receives pollen) + Style + Ovary (contains ovules)

Pollination: Transfer of pollen from anther to stigma (self or cross pollination).

Fertilisation: Pollen grain germinates on stigma, pollen tube grows down the style to the ovule, male gamete fuses with female gamete (egg cell) to form zygote.

After fertilisation: Zygote → Embryo; Ovule → Seed; Ovary → Fruit.

Human Reproductive System

Male: Testes (produce sperm and testosterone) → Vas deferens → Urethra. Accessory glands: seminal vesicles, prostate gland (provide fluid for sperm transport).

Female: Ovaries (produce eggs/ova and oestrogen) → Fallopian tubes (site of fertilisation) → Uterus (implantation and development of embryo) → Vagina.

Menstrual cycle: ~28 days. Uterine lining thickens for possible pregnancy. If fertilisation does not occur, the lining breaks down and is shed (menstruation). Menarche: onset of menstruation. Menopause: cessation of menstruation.

Reproductive Health

Contraceptive methods: Barrier methods (condoms, diaphragm), chemical methods (oral pills), IUDs (copper-T), surgical methods (vasectomy, tubectomy).

Summary

Reproduction ensures continuity of species. Asexual reproduction involves one parent and produces clones. Sexual reproduction involves fusion of male and female gametes and introduces genetic variation. Flowering plants reproduce through pollination and fertilisation. The human reproductive system produces gametes and supports embryo development.

Important Terms

Gamete: A reproductive cell (sperm or egg) that contains half the chromosome number
Zygote: The cell formed by fusion of male and female gametes
Pollination: Transfer of pollen grains from anther to stigma
Fertilisation: Fusion of male and female gametes to form a zygote
Menstruation: Monthly shedding of the uterine lining when no fertilisation occurs

Quick Revision

Asexual reproduction: fission, budding, spore formation, fragmentation, regeneration, vegetative propagation
Flower parts: Sepals, Petals, Stamens (male), Pistil (female)
After fertilisation: ovule → seed, ovary → fruit
Testes produce sperm; ovaries produce ova
Contraception methods: barrier, hormonal, IUD, surgical