Fertilisation in plants and germination

Last time

Before we start: last time, in Asexual and sexual reproduction, and gametes, you learned these points. Here they are again on one card. Keep them in mind, because today builds on them.

From pollen to seed

A pollen grain lands on a stigma, but the male gamete inside is still far from the egg, deep in the ovary. It reaches it by growing a tube. Today: fertilisation in plants, how the seed and fruit form, and what a seed needs to germinate.

After pollination

After a pollen grain lands on the stigma, it grows a pollen tube. The tube grows down through the style, digesting a path with enzymes. It enters the ovule through a small hole called the micropyle.

Fertilisation

The male nucleus travels down the pollen tube. It fuses with the female nucleus inside the ovule. This is fertilisation, and it forms a zygote. Fertilisation happens in the ovule.

Seed and fruit

The zygote divides to form an embryo, and the ovule becomes a seed. The ovary develops into the fruit, which protects the seeds and helps disperse them. The petals, stamens and stigma wither and fall off.

The sequence

Here is the whole sequence. From pollination to seed. The two words students mix up are pollination and fertilisation: one moves pollen, the other fuses nuclei.

Germination

Germination is when a seed starts to grow into a new plant. A seed needs water, oxygen and a suitable temperature to germinate. It does NOT need light, because it uses food stored in the seed until its leaves grow.

Why each is needed

Water: the seed swells, enzymes become active, and stored food is mobilised. Oxygen: for aerobic respiration, to release energy for growth. A suitable temperature: enzymes work best near their optimum.

The germination experiment

Set up four tubes of seeds: one with all three conditions, and three each missing one. Seeds with no water, or no oxygen, or kept cold, do not germinate. Only the tube with water, oxygen and warmth germinates.