Sexual reproduction in plants
Flower structure, pollination, fertilisation and seed dispersal.
Review these first
Learning objectives
What you need to be able to do
Teacher-mapped phrasing — check against the official Cambridge syllabus for exact wording.
- 16.2.1Identify the parts of a flower and describe pollination and fertilisation.
- 16.2.2Compare insect-pollinated and wind-pollinated flowers.
6 minute read
Sexual reproduction in plants
Parts of a flower
Male parts (stamen): the anther produces pollen; the filament holds it up. Female parts (carpel): the stigma receives pollen; the style connects it to the ovary, which contains the ovules. Also: petals (attract insects), sepals (protect the bud).
Pollination versus fertilisation
These are different events and the distinction is examined constantly:
- Pollination is the transfer of pollen from anther to stigma.
- Fertilisation is the fusion of the pollen nucleus with the ovule nucleus, which happens later, after a pollen tube grows down the style.
Pollination is transport; fertilisation is fusion.
Self versus cross pollination
- Self-pollination — pollen lands on the stigma of the same plant. Produces less variation, but does not need another plant.
- Cross-pollination — pollen transfers to a different plant of the same species. Produces more genetic variation, which is the advantage.
Insect versus wind pollination
| Insect-pollinated | Wind-pollinated | |
|---|---|---|
| Petals | large, brightly coloured, scented | small, green, no scent |
| Nectar | present | absent |
| Anthers | inside the flower | hanging outside, exposed |
| Stigma | inside, sticky | outside, large and feathery |
| Pollen | sticky or spiky, small amounts | smooth and light, large amounts |
Every difference follows from the mechanism: insects must be attracted and must brush past the parts, whereas wind requires exposure and sheer quantity.
After fertilisation
The ovule becomes the seed, and the ovary becomes the fruit. Seeds are then dispersed — by wind, animals, water or explosive mechanisms — so that seedlings do not compete with the parent plant for light, water and minerals.
Think of it like this
Insect pollination is a courier with an address; wind pollination is dropping thousands of leaflets from a rooftop. One invests in precision, the other in volume — which explains every structural difference between the flowers.
Worked examples
Method, step by step
A flower has small green petals, no scent, anthers hanging outside and a large feathery stigma. How is it pollinated, and how do you know?
- 1Small green unscented petals and no nectar mean insects are not attracted.
- 2Anthers hanging outside allow pollen to be blown away easily.
- 3A large feathery stigma has a big surface area to catch pollen carried in the air.
It is wind-pollinated — the exposed anthers and feathery stigma are adaptations for releasing and catching airborne pollen, and there is nothing to attract insects.
Common misconceptions
- Using pollination and fertilisation interchangeably. Pollination is transfer; fertilisation is nuclear fusion afterwards.
- Thinking wind-pollinated plants have no flowers. They have flowers, but small, green and unscented ones — there is nothing to attract.
- Saying the ovary becomes the seed. The **ovule** becomes the seed; the **ovary** becomes the fruit.
In the exam
- When comparing pollination types, give the feature **and** the reason: "feathery stigma **to** catch pollen blowing past".
- For dispersal questions, state the benefit: reduced competition with the parent plant for light, water and minerals.