Making
more life.

Meiosis shuffles alleles (crossing over + independent assortment); fertilisation combines two random gametes. Together they generate the variation that natural selection acts on.

• Sperm: small, motile, low energy reserves. Males produce many — competition typically high.
• Eggs: large, immobile, nutrient-rich. Females produce few — investment per gamete is high.
• Differences in gamete strategy drive differences in reproductive strategy — mating systems, parental care, sexual selection.

1. Days 1–5 · Menstruation. Endometrium shed if no pregnancy. FSH starts to rise.
2. Days 6–13 · Follicular phase. FSH stimulates a follicle to develop. The follicle secretes oestradiol; oestradiol stimulates endometrial proliferation. As oestradiol rises, it triggers an LH surge.
3. Day 14 · Ovulation. LH surge triggers release of the egg from the mature follicle.
4. Days 15–28 · Luteal phase. The ruptured follicle becomes the corpus luteum, secreting progesterone. Progesterone maintains the endometrium. If no fertilisation, corpus luteum degenerates → progesterone falls → endometrium shed → next cycle begins.

1. Sperm reach the egg in the oviduct.
2. The acrosome at the sperm head releases hydrolytic enzymes that digest through the egg's outer layers (zona pellucida).
3. One sperm's plasma membrane fuses with the egg's plasma membrane. Nuclei combine.
4. Cortical granules in the egg release, hardening the zona pellucida and blocking polyspermy (more sperm entries).
5. The fertilised egg — now a zygote — begins to divide.

1. Superovulation. The woman is given FSH and LH to stimulate development of multiple follicles simultaneously (instead of just one).
2. Egg collection. Eggs are removed by needle.
3. Fertilisation in vitro. Sperm added to the eggs in a dish; or one sperm injected directly into one egg (ICSI).
4. Embryo culture. Resulting zygotes develop into early embryos in culture for 3–5 days.
5. Embryo transfer. One or two embryos transferred to the uterus.
6. Implantation if successful → pregnancy.

Insect-pollinated flower features

• Bright, large petals to attract insects.
• Nectar and scented compounds as rewards.
• Anthers and stigmas positioned to brush against visiting insects.
• Sticky or spiny pollen that adheres to insects.

• Different timing — anthers and stigmas mature at different times on the same plant.
• Different positions — anthers and stigmas placed so pollen falls away from the same flower's stigma.
• Self-incompatibility — recognition systems where pollen of the same plant is rejected by the stigma at the molecular level. Pollen tubes fail to grow if the genetic match is "self".

Dispersal mechanisms: wind (light, winged or plumed seeds — dandelion, sycamore); animals (sticky, hooked, or edible fruits); water (buoyant seeds like coconut); explosive release.

Germination requires water (rehydrating the seed, activating enzymes), oxygen (for respiration), and suitable temperature. The hormone gibberellin stimulates production of amylase, which breaks down stored starch into glucose — fuel for early growth before photosynthesis begins.