Pollination

Explained

Pollination, and why two kinds of flower look so different

Pollination is the transfer of pollen from an anther to a stigma. A flower cannot move, so it has to persuade something else to carry the pollen for it. Two solutions exist, and every difference between the two flower types comes from which one has been adopted.

Insect pollinated flowers

If an insect is to do the carrying, it has to be attracted and then rewarded. So these flowers have large, brightly coloured petals, a scent, and nectar to draw insects in.

The anthers and stigma are inside the flower, so an insect must brush past them to reach the nectar. The pollen is sticky or spiky, so it clings to the insect's body, and the stigma is sticky so pollen is caught when it arrives.

Because delivery is fairly reliable, only small amounts of pollen are needed.

Wind pollinated flowers

The wind cannot be attracted, so there is nothing to attract it with. These flowers have small, dull petals or none at all, no scent and no nectar. Producing them would be a waste of resources.

Instead the anthers hang outside the flower where moving air can reach them, and the stigmas are large and feathery to catch pollen drifting past. The pollen itself is small, light and smooth so it travels easily on the air.

Because so much pollen lands nowhere useful, these flowers produce it in very large quantities.

The comparison, feature by feature

• Petals: large and coloured for insects, small and dull or absent for wind.
• Scent and nectar: present for insects, absent for wind.
• Anthers: inside the flower for insects, hanging outside for wind.
• Stigma: sticky and inside for insects, feathery and outside for wind.
• Pollen: sticky or spiky and in small amounts for insects, smooth and light in large amounts for wind.
• Pollen grains: fewer for insects, many more for wind.

Answering an adaptation question

Name the feature, then say what it achieves. A feathery stigma does not simply "catch pollen"; it has a large surface area, which increases the chance of catching pollen carried on the wind.

Every adaptation on this page has that two part structure available, and questions asking you to explain rather than describe are asking for the second half.

Pollination is not fertilisation

Pollination is the transfer of pollen to the stigma. Fertilisation happens afterwards, when the male nucleus from the pollen grain fuses with the female nucleus in the ovule, at the end of a pollen tube.

They are two separate events, and using one word where the other is meant is a reliable way to lose an otherwise correct mark.