Reproduction
Summary: Reproduction can be asexual (one parent, genetically identical offspring, e.g. binary fission, budding, runners) or sexual (two parents, fusion of gametes, genetic variation). In flowering plants, reproduction involves flower structure, pollination, fertilisation, seed dispersal, and germination. In humans, the male reproductive system produces sperm; the female system produces eggs. The menstrual cycle is controlled by FSH, LH, oestrogen, and progesterone. After fertilisation, the embryo implants in the uterus and the placenta provides nutrient and gas exchange. Tags: igcse biology reproduction sexual-reproduction asexual flower-structure menstrual-cycle placenta Created: 2026-07-16 Last Updated: 2026-07-16
1. Asexual vs Sexual Reproduction
| Feature | Asexual Reproduction | Sexual Reproduction |
|---|---|---|
| Number of parents | One | Two (usually) |
| Gametes involved? | No | Yes — male and female gametes fuse (fertilisation) |
| Offspring genetic makeup | Genetically identical to parent (clones) | Genetically different from parents — contains a mix of genetic material from both |
| Variation | No (except by mutation) | Yes — genetic variation in offspring |
| Speed of reproduction | Fast — no need to find a mate | Slower — requires mate, gamete production, fertilisation |
| Examples | Binary fission in bacteria, budding in yeast/hydra, runners in strawberry plants, tubers (potatoes), bulbs, tissue culture | Most animals, flowering plants, humans |
Advantages of sexual reproduction:
- Produces genetic variation in offspring
- Variation helps a species survive environmental changes (natural selection)
- Can combine beneficial characteristics from both parents
Advantages of asexual reproduction:
- Fast — can rapidly colonise a habitat
- Only one parent needed — no need to find a mate
- Offspring are identical to parent — if parent is well adapted to the environment, offspring will be too
2. Flower Structure and Pollination
Flower Structure
| Part | Description and Function |
|---|---|
| Petals | Often brightly coloured — attract insects and other pollinators |
| Sepals | Green, leaf-like structures that protect the flower bud before it opens |
| Stamen (male part) | Consists of anther (produces pollen grains containing male gametes) and filament (stalk supporting the anther) |
| Carpel / Pistil (female part) | Consists of stigma (sticky top — catches pollen grains), style (tube connecting stigma to ovary), and ovary (contains ovules — female gametes) |
| Nectary | Produces sugary nectar — attracts pollinators (insects, birds) |
Pollination
Pollination is the transfer of pollen grains from the anther to the stigma.
Self-pollination: Pollen transferred from anther to stigma of the same flower or same plant. Cross-pollination: Pollen transferred from anther of one plant to stigma of a different plant of the same species.
| Feature | Insect-Pollinated Flowers | Wind-Pollinated Flowers |
|---|---|---|
| Petals | Large, brightly coloured, scented | Small, dull, no scent |
| Nectar | Present (attracts insects) | Absent |
| Anthers | Inside the flower (insect brushes past them) | Hang outside the flower (exposed to wind) |
| Stigma | Small, sticky, inside flower | Large, feathery, hanging outside (catch pollen from air) |
| Pollen grains | Sticky/spiky, relatively large, fewer produced | Smooth, light, small, produced in very large quantities |
| Examples | Rose, sunflower, pea | Grass, wheat, maize, oak |
Fertilisation in Plants
- A pollen grain lands on the stigma
- The pollen grain germinates, growing a pollen tube down through the style towards the ovary
- The male nucleus travels down the pollen tube
- The pollen tube enters an ovule through the micropyle (small hole)
- The male nucleus fuses with the female nucleus inside the ovule — this is fertilisation
- The fertilised ovule develops into a seed
- The ovary develops into a fruit (which protects and helps disperse the seeds)
Seed Dispersal
Seeds must be dispersed away from the parent plant to avoid competition for light, water, and nutrients.
| Method | Seed/Fruit Adaptations | Examples |
|---|---|---|
| Wind | Light, small, feathery hairs or wings | Dandelion (parachute of hairs), sycamore (winged), poppy (pepperpot) |
| Animals (external) | Hooks/barbs that catch on animal fur | Burdock, goose grass |
| Animals (internal) | Brightly coloured, fleshy, edible fruit — seeds pass through gut undigested | Apple, berry, tomato |
| Self-dispersal (mechanical) | Pods that dry out and split open explosively, scattering seeds | Pea, bean, lupin |
| Water | Light, buoyant, waterproof | Coconut (fibrous husk), water lily |
Germination
Germination is the process by which a seed develops into a seedling.
Conditions required for germination:
- Water: Activates enzymes (e.g. amylase breaks down stored starch to glucose for respiration). Swells the seed, splitting the seed coat (testa)
- Oxygen: Needed for aerobic respiration to release energy (ATP) for growth
- Warmth (suitable temperature): Optimum temperature for enzyme activity (typically ~20-30 degrees C)
Light is NOT usually required for germination (seeds can germinate underground). The seed uses stored food reserves (in cotyledons or endosperm) until the seedling can photosynthesise.
3. Human Reproductive Systems
Male Reproductive System
| Structure | Function |
|---|---|
| Testes (singular: testis) | Produce sperm (male gametes) by meiosis. Produce testosterone (male sex hormone). Located in the scrotum (outside body) — sperm development requires a temperature slightly below body temperature |
| Epididymis | Coiled tube where sperm are stored and mature |
| Sperm duct (vas deferens) | Tube carrying sperm from the epididymis to the urethra |
| Prostate gland | Secretes a fluid that makes up part of semen — contains enzymes and nutrients to nourish and activate sperm |
| Seminal vesicles | Secrete fluid rich in fructose (provides energy for sperm) — part of semen |
| Urethra | Tube running through the centre of the penis. Carries semen (sperm + glandular fluids) during ejaculation; also carries urine from the bladder |
| Penis | External organ that delivers sperm into the female reproductive tract during sexual intercourse |
Female Reproductive System
| Structure | Function |
|---|---|
| Ovaries (singular: ovary) | Produce eggs (female gametes / ova) by meiosis — one approximately every 28 days (ovulation). Produce oestrogen and progesterone |
| Oviducts (Fallopian tubes) | Tube lined with cilia. Carries the released egg from the ovary towards the uterus. Site of fertilisation (sperm meets egg) |
| Uterus (womb) | Hollow, muscular organ with a thick, blood-rich lining (endometrium). Where a fertilised egg implants and the embryo/foetus develops during pregnancy |
| Cervix | Ring of muscle at the base of the uterus. Keeps the developing foetus in place during pregnancy; dilates (widens) during birth |
| Vagina | Passage receiving the penis during intercourse; birth canal through which the baby passes during delivery |
4. The Menstrual Cycle
The menstrual cycle is a ~28-day cycle controlled by hormones from the pituitary gland (FSH, LH) and the ovaries (oestrogen, progesterone).
Hormones of the Menstrual Cycle
| Hormone | Source | Function |
|---|---|---|
| FSH (Follicle Stimulating Hormone) | Pituitary gland (brain) | Stimulates the development of a follicle (containing an egg) in the ovary. Stimulates the ovary to produce oestrogen |
| Oestrogen | Developing follicle in ovary | Repairs and thickens the uterine lining (endometrium) after menstruation. Rising oestrogen levels inhibit FSH and stimulate LH release from the pituitary |
| LH (Luteinising Hormone) | Pituitary gland | Causes ovulation (release of the mature egg from the follicle) around day 14. The ruptured follicle becomes the corpus luteum |
| Progesterone | Corpus luteum (from the ruptured follicle) | Maintains the thick uterine lining (endometrium), preparing it for implantation of an embryo. Inhibits FSH and LH — preventing further egg development during pregnancy |
Cycle Summary
| Phase | Days (approx.) | Events |
|---|---|---|
| Menstruation | Days 1-5 | Uterine lining breaks down and is shed (bleeding) if no fertilisation occurred in the previous cycle |
| Follicular phase | Days 1-13 | FSH stimulates follicle development. Oestrogen levels rise — repairs uterine lining |
| Ovulation | Day 14 | LH surge causes the mature egg to be released from the ovary into the oviduct |
| Luteal phase | Days 15-28 | Corpus luteum secretes progesterone — maintains uterine lining. If no fertilisation, corpus luteum degenerates → progesterone drops → menstruation begins |
Fertilisation and Implantation
- Fertilisation: A sperm penetrates the egg in the oviduct. The sperm and egg nuclei fuse, forming a zygote
- The zygote divides by mitosis as it travels down the oviduct, becoming a ball of cells (morula → blastocyst)
- Implantation: The blastocyst embeds into the thick uterine lining (endometrium) ~7-9 days after fertilisation
- The implanted embryo produces the hormone hCG (human chorionic gonadotropin), which keeps the corpus luteum producing progesterone — preventing menstruation
The Placenta
The placenta develops from embryonic and maternal tissues. It is the interface between the mother’s blood and the developing foetus — though the two blood supplies do NOT mix.
Functions of the placenta:
- Nutrient exchange: Glucose, amino acids, vitamins, minerals diffuse from mother’s blood to foetal blood
- Gas exchange: Oxygen diffuses from mother → foetus; CO2 diffuses from foetus → mother
- Waste removal: Urea and other waste products diffuse from foetus → mother’s blood for excretion
- Protection: Prevents most bacteria from crossing (though viruses like rubella and HIV can cross)
- Hormone production: Produces progesterone to maintain the pregnancy
The umbilical cord connects the foetus to the placenta — contains the umbilical artery and vein.
Amniotic fluid: Surrounds the foetus in the amniotic sac — protects against mechanical shock/bumps, allows foetal movement.
Birth Control (Contraception)
| Method | Type | How It Works |
|---|---|---|
| Oral contraceptive pill | Hormonal | Contains oestrogen and progesterone — inhibits FSH/LH release, preventing ovulation. Must be taken daily |
| Condom | Barrier | Prevents sperm reaching the egg. Also protects against STIs |
| Diaphragm / Cap | Barrier | Rubber cap placed over cervix — prevents sperm entering uterus. Used with spermicide |
| IUD (coil) | Intrauterine device | Inserted into uterus — prevents implantation of a fertilised egg. Copper IUDs are toxic to sperm |
| Vasectomy | Surgical (male) | Sperm ducts are cut and sealed — no sperm in semen |
| Tubal ligation | Surgical (female) | Oviducts are cut/sealed — eggs cannot reach the uterus |
| Rhythm / natural method | Behavioural | Avoiding intercourse around ovulation (day 14). Unreliable — cycle timing varies |
Related Notes
- Inheritance — Gametes carry genetic information; meiosis produces haploid gametes
- Variation and Selection — Sexual reproduction produces genetic variation for natural selection
- Coordination and Response — FSH, LH, oestrogen, progesterone, and testosterone as hormones
- Cell Structure and Organisation — Sperm cells as specialised cells
- IGCSE-Bio-Index — Full IGCSE Biology index
Sources
- BBC Bitesize GCSE Biology — Reproduction in plants / Reproduction in humans, BBC (free educational resource)
- OpenStax Biology 2e — Chapter 43: Animal Reproduction and Development / Chapter 32: Plant Reproduction, Rice University (free, CC BY 4.0)
- Cambridge IGCSE Biology 0610 — Topic 16: Reproduction, Cambridge Assessment International Education
- CK-12 Biology for High School — Reproduction chapter, CK-12 Foundation (free, CC BY-NC 3.0)
Common Misconceptions
| Misconception | Reality |
|---|---|
| ”Pollination is the same as fertilisation” | Pollination is the transfer of pollen to the stigma. Fertilisation is the fusion of male and female gametes inside the ovule — they are different processes |
| ”All flowers are pollinated by insects” | Many flowers (especially grasses, cereals) are wind-pollinated — they have small, dull petals, large feathery stigmas, and produce lots of light pollen |
| ”The male nucleus travels down the style without a pollen tube” | The pollen grain grows a pollen tube down through the style to deliver the male nucleus to the ovule |
| ”Seeds need light to germinate” | Most seeds do NOT need light for germination — they need water, oxygen, and warmth. Light is needed after germination for photosynthesis |
| ”The placenta mixes maternal and foetal blood” | The two blood supplies are separate — the placenta allows diffusion of substances between them but the blood does not mix. This is why a mother and foetus can have different blood types |
| ”FSH is produced by the ovaries” | FSH and LH are produced by the pituitary gland in the brain. The ovaries produce oestrogen and progesterone |