The flower
The flower is the reproductive organ of a plant. Its male part is the stamen — the anther (makes pollen) on a filament. Its female part is the carpel — the stigma (receives pollen), a style, and the ovary (contains ovules). Petals attract insects; sepals protect the bud.
Pollination
Pollination is the transfer of pollen from an anther to a stigma. In self-pollination pollen lands on the same plant; in cross-pollination it goes to a different plant, giving more variation. Pollen is carried by insects (bright, scented flowers with sticky pollen) or by wind (small, dull flowers with feathery stigmas and light pollen).
| Feature | Insect-pollinated | Wind-pollinated |
|---|---|---|
| Petals | large, bright, scented | small or absent, dull |
| Pollen | sticky | smooth, light, plentiful |
| Stigma | sticky, inside | feathery, hanging outside |
| Nectar | present | absent |
Fertilisation and seeds
After pollination, a pollen tube grows down the style to the ovule, and the male nucleus fuses with the female nucleus — fertilisation. The fertilised ovule becomes a seed, and the ovary becomes a fruit. A seed contains an embryo and a food store, and can lie dormant until conditions are right.
Seed dispersal and germination
Seeds are dispersed away from the parent — by wind, animals, water or explosive pods — which reduces competition for light, water and minerals. A seed germinates when it has water, oxygen and a suitable temperature, living off its food store until it can photosynthesise.
Why disperse?
If all seeds fell at the parent's base they would compete with each other and the parent for light, water and minerals. Dispersal spreads them out, improving survival.
A worked example
A flower has small, dull petals, no scent or nectar, anthers hanging outside, and a large feathery stigma. How is it pollinated?
- Dull, scentless, nectarless flowers do not attract insects.Insect flowers invest in attraction; this one does not.
- Anthers hang outside so the wind blows pollen away.Exposed anthers release pollen to the air.
- A feathery stigma has a large area to catch airborne pollen.It filters pollen from the wind.
It is wind-pollinated: dull and scentless, with exposed anthers and a feathery stigma to release and catch airborne pollen.
Adaptations for seed dispersal
Seeds and fruits are adapted to the way they travel. Wind-dispersed seeds are light with wings or parachutes of hair (sycamore, dandelion). Animal-dispersed fruits are either fleshy and tasty (eaten, the seeds passing through unharmed) or covered in hooks that catch on fur. Water-dispersed seeds (coconut) float, and some pods dry and explode, flinging seeds away. Each adaptation carries the seed far from the parent, reducing competition.
| Dispersal | Adaptation |
|---|---|
| Wind | light, with wings or hairs |
| Animal (eaten) | fleshy, brightly coloured fruit |
| Animal (carried) | hooks that catch on fur |
| Water | buoyant, waterproof (e.g. coconut) |
Asexual reproduction in plants
Many plants also reproduce asexually — from a single parent, giving genetically identical offspring. Strawberries send out runners that root and grow new plants; onions and daffodils form bulbs; potatoes grow from tubers. Growers exploit this with cuttings and grafting (vegetative propagation), which reproduce a prized plant exactly. It is fast and needs no pollinator, but the lack of variation is a weakness if conditions change.