Chapter at a Glance
How Do Organisms Reproduce? — the essentials in one place.
- Reproduction is not needed to keep an individual alive, but it keeps the species going and gives populations stability.
- A basic event in reproduction is making a DNA copy (plus new cellular apparatus). DNA copying is never perfect → variations → the basis of evolution.
- Two broad modes: asexual (one parent, little variation) and sexual (two parents, more variation).
Asexual Reproduction — Quick Recap
| Method | Example | Key idea |
|---|---|---|
| Binary fission | Amoeba, bacteria | Cell splits into two |
| Multiple fission | Plasmodium | Splits into many at once |
| Budding | Hydra, yeast | Bud grows out, detaches |
| Fragmentation | Spirogyra | Breaks into pieces that grow |
| Regeneration | Hydra, Planaria | Body pieces grow into whole (not true reproduction) |
| Spore formation | Rhizopus | Spores in sporangia, thick-walled |
| Vegetative propagation | Potato, Bryophyllum, sugarcane, rose | New plant from root/stem/leaf |
Tissue culture: growing many disease-free plants from a piece of tissue → callus → plantlets.
Sexual Reproduction in Plants — Quick Recap
- Flower whorls: sepals (protect) → petals (attract) → stamens (male: anther + filament) → pistil (female: stigma + style + ovary).
- Unisexual flower (papaya, watermelon) vs bisexual flower (Hibiscus, mustard).
- Pollination = anther → stigma (self or cross). Fertilisation = male germ-cell + egg → zygote (pollen tube carries the male gamete through the style).
- After fertilisation: ovule → seed; ovary → fruit; other parts shrivel. Seed germinates into a seedling.
Pollination vs Fertilisation
| Pollination | Fertilisation |
|---|---|
| Transfer of pollen to stigma | Fusion of gametes → zygote |
| No fusion | Fusion occurs |
| Happens first | Happens after pollination |
Human Reproductive Systems — Quick Recap
Male system
- Testes (in scrotum, outside body for lower temperature) → make sperms + testosterone.
- Vas deferens → carries sperm; seminal vesicle + prostate → add fluid (transport + nutrition = semen).
- Urethra → common passage for urine + sperm; penis delivers sperm.
- Sperm = head (DNA) + tail (motile).
Female system
- Ovaries → make eggs (thousands at birth; one/month after puberty) + hormones.
- Oviduct/fallopian tube → site of fertilisation; uterus → site of development; cervix → opening; vagina → receives sperm, birth canal.
- Egg = large, non-motile, stores food.
Puberty
- Girls: breast growth, nipple darkening, menstruation begins.
- Boys: facial hair, voice cracks, penis enlargement (driven by testosterone).
Fertilisation, Pregnancy & Menstruation — Quick Recap
The chain: Sperm + Egg → Zygote (oviduct) → Embryo (implants in uterus) → Foetus (organs form) → Birth (~9 months; rhythmic uterine contractions).
Placenta: disc in uterine wall; villi (embryo side) + blood spaces (mother side) → large surface area → glucose + O₂ to embryo, wastes to mother.
Menstruation: uterus lining thickens monthly; if egg not fertilised → lining breaks down → blood + mucus shed for ~2–8 days.
Reproductive Health, Contraception & STDs — Quick Recap
Contraceptive methods
| Type | Example | How it works | STD protection? |
|---|---|---|---|
| Barrier | Condom | Blocks sperm | Yes |
| Hormonal | Oral pills | Stop egg release | No |
| IUCD | Loop, copper-T | Placed in uterus | No |
| Surgical | Vasectomy / tubectomy | Block vas deferens / fallopian tube | No |
STDs (learn by cause)
- Bacterial: gonorrhoea, syphilis.
- Viral: warts, HIV–AIDS.
- Prevention: condom (barrier method).
Social points
- Sex ratio must be maintained; female foeticide lowers the child sex ratio; prenatal sex determination is illegal.
- Population size depends on birth rate and death rate.
Master One-Liners (Morning-of-Exam Revision)
Read these last, just before the paper.
- Basic event in reproduction = making a DNA copy.
- Variation → survival of the species + basis of evolution.
- Binary fission = two; multiple fission = many.
- Budding = Hydra, yeast; fragmentation = Spirogyra; spores = Rhizopus.
- Vegetative propagation → offspring genetically identical to parent.
- Stamen = anther + filament; Pistil = stigma + style + ovary.
- Pollination = pollen to stigma; Fertilisation = gamete fusion → zygote.
- Ovule → seed; ovary → fruit.
- Testes outside body → lower temperature for sperm formation.
- Urethra = common passage for urine + sperm (male only).
- Fertilisation = oviduct; development = uterus.
- Embryo nourished by placenta (villi + blood spaces).
- No fertilisation → menstruation (lining shed, 2–8 days).
- Only barrier methods protect against STDs.
- Prenatal sex determination is banned by law.