Reproduction

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🌸 Parts of a flower (labelling).

Male parts: the stamen (anther + filament)

  • Anther: makes the pollen (contains the male gametes)

  • Filament: the stalk that holds the anther up

Female parts: the carpel / pistil (stigma + style + ovary)

  • Stigma: sticky top where pollen lands

  • Style: tube connecting the stigma to the ovary

  • Ovary: contains the ovules (eggs) and becomes the fruit after fertilisation

  • Ovule: becomes the seed once fertilised

Other parts

  • Petals: coloured, often scented, to attract pollinators

  • Sepals: green leaf-like parts that protect the flower bud before it opens

Pollination → fertilisation → fruit

  1. Pollen moves from anther to stigma (pollination)

  2. A pollen tube grows down the style to the ovary

  3. The sperm nucleus joins the ovum (fertilisation) → zygote → embryo

  4. Ovule becomes the seed, and the ovary swells into the fruit

🌼 Pollination types

  • Self-pollination: pollen lands on the same plant’s stigma. It’s reliable but gives little genetic variation.

  • Cross-pollination: pollen comes from another plant, carried by wind or insects. It gives more genetic diversity, but the plant depends on pollinators.

Insect-pollinated vs wind-pollinated flowers


Insect

Wind

Petals

big, bright, scented

small, dull or none

Nectar

yes

no

Anthers/stigma

inside the flower

hang outside

Pollen

sticky/spiky, less of it

light, smooth, huge amounts

🌱 Asexual reproduction

  • Definition: one parent, and the offspring are genetically identical clones.

  • Types:

    • Binary fission (bacteria)

    • Budding:An outgrowth (bud) forms on the parent organism, develops, and separates into a clone (e.g., yeast, hydra)

    • Regeneration (planaria)

    • Spores: Durable, lightweight reproductive cells that disperse and grow into new organisms in favourable conditions (e.g., fungi).

    • Runners: Horizontal stems that run along the ground, forming roots and shoots at nodes to produce new plants (e.g., strawberry).

    • Suckers: Underground shoots that sprout from the parent plant's root system to form independent plants (e.g., bamboo).

    • Tubers (potato)

    • Bulbs (onion)

    • Cuttings: A severed plant part (such as a stem or leaf) that roots and grows into a whole new plant (e.g., sugarcane, rose).

    • Parthenogenesis (whiptail lizards, aphids, Komodo dragons)

  • Advantages: fast, no mate or pollination needed, colonises an area quickly

  • Disadvantages: no genetic variation, so the whole population is vulnerable to disease or environmental change

💑 Sexual reproduction

  • Gametes (sex cells) are made in the gonads (testes and ovaries). Each gamete carries half the genetic material of a body cell.

  • Fertilisation is when the sperm and egg nuclei join, forming a zygote.

  • Advantages: genetic diversity, so the population is better at surviving change

  • Disadvantages: costs more energy, the organism needs to find a mate, and it’s slower

  • Internal fertilisation (humans, elephants, eagles): fewer offspring, but each has a better chance of survival

  • External fertilisation (fish, amphibians): lots of eggs, but many are lost to predators

👩 Female reproductive system

  • Ovaries: make eggs and hormones

  • Ovarian ligament: holds the ovary in place

  • Oviduct (fallopian tube): carries the egg to the uterus, and is where fertilisation usually happens

  • Uterus: where the embryo implants and the foetus develops

  • Endometrium: the uterus lining

  • Cervix: the neck of the uterus

  • Vagina: muscular canal from the cervix to outside the body

👨 Male reproductive system

  • Testes: make sperm and testosterone. They sit in the scrotum because sperm need a slightly cooler temperature than inside the body.

  • Scrotum: skin sac holding the testes

  • Epididymis: stores sperm as it matures

  • Vas deferens (sperm duct): carries sperm to the urethra

  • Seminal vesicle and prostate gland: add fluid to sperm, making semen

  • Cowper’s gland: adds fluid

  • Urethra: carries urine or semen out (never at the same time)

  • Penis: external organ

🤰 Placenta

  • Nutrients move from mother to foetus by diffusion across the placenta.

  • The umbilical cord connects the placenta to the foetus.

  • Nutrients and oxygen go in, and wastes like CO₂ and urea go out.

⚖ r vs K selection

  • r-selected (insects, many plants): lots of small offspring, no parental care, short life, unstable environments

  • K-selected (most mammals): few large offspring, lots of parental care, long life, stable environments

  • Fish sit in the middle.