Flowers, pollination and cross-pollination

Last time

Before we start: last time, in Fertilisation in plants and germination, you learned these points. Here they are again on one card. Keep them in mind, because today builds on them.

Why flowers are beautiful

Flowers are not there for us. Their colours, scents and nectar are there to attract insects. A flower is the plant's organ of sexual reproduction. Today: the parts of a flower, how pollen gets from one flower to another, and why it matters.

The parts of a flower

Here is an insect-pollinated flower. The sepals protect the bud. The petals attract insects. The stamens, the anther and filament, are male. The carpel, the stigma, style and ovary, is female.

Male parts

The stamen is the male part. It has an anther on a stalk called the filament. The anther makes pollen grains, which contain the male gametes. The filament holds the anther up, in a good position.

Female parts

The carpel is the female part: stigma, style and ovary. The stigma is sticky and catches pollen. The ovary contains ovules, and each ovule contains a female gamete.

Pollination

Pollination is the transfer of pollen grains from an anther to a stigma. It happens before fertilisation. Pollination is not the same as fertilisation. Pollen is carried by insects or by the wind.

Insect or wind?

Flowers are adapted to their pollinator. Insect flowers attract insects; wind flowers let the wind do the work. Look at the stamens and stigmas: wind flowers hang them outside.

Self and cross-pollination

Self-pollination is the transfer of pollen from the anther to the stigma of the same flower, or another flower on the same plant. Cross-pollination is the transfer of pollen to the stigma of a flower on a different plant of the same species.

Which is better?

Cross-pollination mixes the genes of two plants, so the seeds show more variation. This helps a species adapt to change, but it depends on pollinators and wastes more pollen. Self-pollination is more reliable, but gives less variation.