Year 1 · Reproduction in plants and animals · Section 6.3
Fertilisation
The pollen tube
Each ovule contains an egg cell with a nucleus. When compatible pollen lands on the stigma, a pollen tube can grow from the pollen grain.
The tube grows through the style towards an ovule in the ovary. Male sex cells travel through the pollen tube towards the egg cell.
When the tube reaches the ovule, it releases the male sex cells. A male nucleus fuses with the egg-cell nucleus. This fusion is fertilisation, producing a fertilised egg cell, or zygote, with chromosomes from both parents.
The fertilised egg cell
After fertilisation, the zygote divides repeatedly. These divisions form an embryo, the beginning of a new plant. The ovule develops into a seed containing the embryo. During germination, the embryo grows into a seedling.
Several pollen tubes can grow through one style towards different ovules. This allows several egg cells to be fertilised and several seeds to develop.
In the usual sexual life cycle of a flowering plant, an ovule develops into a seed after fertilisation. An unfertilised ovule normally does not develop into a seed.
Glossary
- Fertilisation
- Fusion of a male sex-cell nucleus with a female sex-cell nucleus, producing a zygote.
- Embryo
- The young plant formed from a fertilised egg cell through repeated cell division.
- Pollen tube
- A tube growing from a pollen grain through the style towards an ovule, carrying male sex cells.
- Seed
- A structure developing from an ovule after fertilisation and containing an embryo that can grow into a seedling.