Class 10 Science Notes — Chapter 7: How Do Organisms Reproduce?
Asexual and sexual reproduction in plants and humans, and reproductive health.
Detailed NCERT notes
- Reproduction ensures continuity of species and variation via DNA copying.
- Asexual reproduction: single parent, offspring genetically identical (clones).
- Fission — binary (Amoeba), multiple (Plasmodium).
- Budding — Hydra, yeast.
- Fragmentation — Spirogyra.
- Regeneration — Planaria (specialised cells).
- Vegetative propagation — potato tuber (eyes), sugarcane, rose (cuttings), Bryophyllum (leaf buds); used commercially to preserve variety.
- Spore formation — Rhizopus (bread mould).
- Tissue culture — laboratory technique using totipotent cells.
- Sexual reproduction: two parents; gametes fuse (fertilisation); brings variation via meiosis + random fertilisation.
- Reproduction in flowering plants (angiosperms):
- Male: stamen (anther + filament). Anther makes pollen.
- Female: pistil (stigma + style + ovary). Ovary has ovules.
- Pollination: transfer of pollen from anther to stigma; self- or cross-pollination.
- Fertilisation: pollen tube grows through style → male gamete fuses with egg in ovule → zygote → embryo → seed; ovary → fruit.
- Reproduction in humans:
- Puberty: hormonal changes; secondary sexual characters develop.
- Male: testes (produce sperm & testosterone), vas deferens, seminal vesicles, prostate, urethra, penis.
- Female: ovaries (release ovum, produce oestrogen/progesterone), fallopian tubes (site of fertilisation), uterus (site of implantation and development), vagina.
- Menstrual cycle: 28-day cycle; ovulation ~day 14; if no fertilisation, uterine lining sheds (menstruation).
- Fertilisation in fallopian tube → zygote → embryo → implants in uterus → placenta forms (nutrition + gas exchange) → foetus → birth (~9 months).
- Reproductive health: safe sex prevents STDs (gonorrhoea, syphilis, HIV/AIDS). Contraceptive methods: barrier (condom), chemical (pills), surgical (vasectomy/tubectomy), IUCD.
- Sex determination: XX (female), XY (male); father's Y chromosome determines male offspring.
Formulas & key results
Mind map
- Asexual: fission, budding, fragmentation, regeneration, vegetative, spore, tissue culture
- Sexual in plants: pollination → fertilisation → fruit/seed
- Sexual in humans: gametogenesis → fertilisation → placenta → foetus
- Reproductive health: STDs, contraception
Tricks & shortcuts
- Asexual = clones (no variation); sexual = variation (advantage in evolution).
- Pollination is transfer only; fertilisation is fusion.
Common mistakes to avoid
- Confusing pollination with fertilisation.
- Mixing up male vs female parts of a flower.
Competency-based questions & answers
- Q. Why is variation useful for a species?A. It allows the species to survive changing environments — some individuals may have traits suited to new conditions (drives natural selection).
- Q. Why is DNA copying essential in reproduction?A. It transmits parental traits to offspring; small variations in copying create diversity that fuels evolution.
- Q. Why is the male gamete smaller than the female gamete?A. Male gamete carries only genetic material and is designed for motility; the female gamete stores nutrients for the embryo.