Reproduction
Asexual reproduction
One parent, no gametes, offspring are genetically identical (clones).
| Method | Organisms |
|---|---|
| Binary fission | Amoeba, paramecium, bacteria |
| Budding | Yeast, hydra |
| Fragmentation | Spirogyra, planaria |
| Spore formation | Fungi (Rhizopus), ferns, mosses |
| Regeneration | Hydra, planaria, starfish |
| Vegetative propagation | Plants: cutting (rose, sugarcane), layering (jasmine), grafting (mango), tissue culture; leaves of Bryophyllum; tubers (potato); bulbs (onion) |
Sexual reproduction in plants
- Flower parts: sepals (calyx, protect), petals (corolla, attract insects), stamen (male: anther produces pollen, filament), pistil / carpel (female: stigma, style, ovary; the ovary has ovules).
- Pollination: transfer of pollen from anther to stigma: self-pollination (same flower) or cross-pollination (by wind, water, insects, birds, animals).
- Fertilisation: the male gamete fuses with the egg in the ovule, forming a zygote. Double fertilisation is a feature of angiosperms.
- After fertilisation: ovary becomes the fruit, ovule becomes the seed. Seed has a seed coat, embryo and cotyledons.
- Germination: seed grows into a seedling; needs water, air, suitable temperature.
- Seed dispersal by wind (maple, dandelion, drumstick), water (coconut, lotus), animals (burr, xanthium), explosion (castor, pea).
- Parthenocarpy: fruit without fertilisation (seedless banana, grapes).
Human reproduction
| Male system | Female system |
|---|---|
| Testes (in the scrotum): sperms and testosterone; vas deferens; seminal vesicle and prostate make semen; urethra | Ovaries (egg and hormones), fallopian tubes (oviducts) (fertilisation here), uterus (womb) (embryo develops), vagina |
- Gametes: sperm (male) and ovum (female). Fertilisation gives a zygote, which divides to become an embryo, then a foetus; it implants in the uterus lining.
- Placenta supplies food and oxygen to the embryo through the umbilical cord and removes wastes.
- Gestation (pregnancy) lasts about 9 months (about 280 days).
- Menstrual cycle: about 28 days; ovulation (release of egg) occurs about the 14th day. Menarche is the first period; menopause is its end (about 45 to 50 years).
- Sex determination in humans: females XX; males XY. The father's sperm (X or Y) decides the baby's sex.
- Puberty: age of sexual maturity (about 10 to 12 for girls, 12 to 14 for boys); adolescence is the 11 to 19 age group.
- Twins: identical (one egg splits) and fraternal (two eggs). IVF (in vitro fertilisation, test-tube baby; Louise Brown, 1978; India: Harsha, 1986) helps infertility.
- Contraception: barrier (condoms), IUDs (copper-T), oral pills (hormonal), surgical (vasectomy, tubectomy). Condoms also prevent STIs. Amniocentesis (sex-determination test) is banned; female foeticide is illegal (PCPNDT Act).
- Metamorphosis in animals: frog (egg, tadpole, adult), butterfly and silkworm (egg, larva, pupa, adult) controlled by hormones.
Keep practising
Notes are only half the work. Test yourself with questions and discuss doubts with other aspirants.
Prepared for exam revision from the NCERT Science textbooks for Classes 6 to 10 and standard sources. Space missions, awards and records change, so check official sources for recent facts. Found a mistake? Tell us.