Fertilisation
Fertilisation
- Fertilisation occurs when a pollen nucleus fuses with an ovum nucleus in the ovule
- As the pollen has no ‘tail’ to swim to the ovary of a plant, in order to reach the ‘female’ nucleus in the ovary it has to grow a pollen tube
- This only happens if the pollen grain has landed on the right kind of stigma (i.e. of the same species as the flower the pollen came from)
- The nucleus inside the pollen grain slips down the tube as it grows down the style towards the ovary
- The ovary contains one or more ovules which each contain an ovum with a female nucleus that a male pollen nucleus can fuse with
- Once the nuclei have joined together, that ovule has been fertilised and a zygote has been formed
- The zygote will start to divide and eventually form a seed within the ovule
- As different plants have different numbers of ovules, this explains why different fruits (which develop from the ovary) have different numbers of seeds (which develop from the ovules)
Growth of pollen tube & fertilisation diagram
Growth of the pollen tube occurs after pollination and is necessary to provide a means for the pollen nucleus to fuse with the ovum nucleus during fertilisation
Examiner Tip
Students often get confused between pollination and fertilisation in plants, but they are not the same thing.
Think of pollination as the plant’s equivalent to human sexual intercourse – after sex, the male sex cells (sperm) have been deposited into the female. But, for fertilisation to occur, the nucleus from a male sperm cell has to fuse with the nucleus of a female sex cell (egg) and the sperm has to travel to find the egg before this happens. It’s exactly the same in plants!
