Flower structure and pollination
From flower parts to pollen transfer.
The flower is the reproductive structure of an angiosperm (flowering plant). Most flowers are bisexual (hermaphrodite), carrying both male and female parts.
Outer (non-reproductive) parts:
- Sepals β usually green; enclose and protect the developing flower bud.
- Petals β in insect-pollinated flowers they are large, brightly coloured and may produce scent to attract pollinators.
Male part β the stamen:
- Anther β produces and releases pollen grains (which contain the male gametes).
- Filament β stalk that holds the anther in position.
Female part β the carpel (pistil):
- Stigma β sticky/feathery surface that receives pollen grains.
- Style β supports the stigma and is the route the pollen tube grows down.
- Ovary β contains one or more ovules; each ovule holds an egg cell and will become a seed after fertilisation.
- Nectary β produces nectar, a sugary reward, in insect-pollinated flowers.
Pollination is the transfer of pollen from an anther to a stigma.
- Self-pollination β pollen lands on the stigma of the same plant (or even the same flower). Reduces genetic variation but guarantees a mate.
- Cross-pollination β pollen is carried to the stigma of a different plant of the same species. Increases genetic variation, which is favourable for evolution and disease resistance.
Adaptations for pollination β a comparison:
| Feature | Insect-pollinated | Wind-pollinated |
|---|---|---|
| Petals | Large, brightly coloured | Small, dull/green or absent |
| Scent & nectar | Present (attract insects) | Absent |
| Pollen | Sticky/spiky, large grains, small amount | Smooth, light, large amount |
| Anthers | Inside flower, firm | Dangle outside, loose |
| Stigma | Sticky, inside flower | Large, feathery, hangs outside to catch pollen |
Mutualism in pollination. Insect (and bird/bat) pollination is a mutualism: the pollinator gains food (nectar/pollen) while the plant gains pollen transfer. This relationship underpins the reproduction of most flowering plants, many food crops (e.g. apples, almonds, oilseed) and overall biodiversity β so pollinator decline threatens both ecosystems and agriculture.
- Stamen = anther + filament (male); carpel = stigma + style + ovary/ovule (female).
- Pollination = pollen moved anther β stigma.
- Self vs cross pollination differ in genetic variation.
- Insect flowers: colourful, scented, sticky pollen; wind flowers: dull, feathery stigma, light pollen.