In I/GCSE Biology of human reproduction, male gametes are transferred to the female gametes by pollination. In other words, the pollen grains are transferred from the anthers to the stigma. This can be carried out either by wind or insects. Fertilisation then takes place and the zygote that’s formed develops into a seed and becomes enclosed in a fruit.
Self-pollination and cross-pollination
In I/GCSE Biology, self-pollination is when pollen grains are transferred to the stigma within the same flower. Cross-pollination is when pollen grains are transferred to the stigma of a different flower.
- Positions of the stamen and stigma are enclosed within flower so the insect must make contact.
- Stigma is sticky so pollen grains attach from insects.
- Petals are large and brightly coloured to attract insects.
- Nectaries are present, containing nectar which serves as a ‘reward’ for insects.
- Pollen grains are large and sticky, so they can stick to insects’ bodies.
Wind-Pollinated Plant 🌬️
- Stamens are exposed so the wind can easily blow the pollen away.
- Stigmas are exposed and feathery to catch pollen blowing in the wind.
- Petals are small and not brightly coloured – usually green.
- No nectaries.
- Pollen grains are smaller, smooth inflated grains to carry in the wind (???).
- To transfer the nucleus of the pollen grain to the ovum, the pollen grain grows a tube which digests its way through the tissue of the style and into the ovary.
- It then grows around, and to the opening of the ovule.
- The tip of the tube dissolves and allows the pollen grain nucleus to move out of the tube and into the ovule.
- It then fertilises the ovum nucleus.
Seed and Fruit Formation 🥝
- The zygote develops into an embryonic plant with a small root (radicle) and a shoot (plumule).
- The other contents of the ovule develop into cotyledons which will be a food store for the young plant when the seed germinates.
- The ovule wall becomes a seed coat or testa.
- The ovary wall becomes the fruit coat.
Dispersal of Fruits and Seeds
Plants disperse their seeds to avoid competition for the available resources.
Type of Dispersal
Structure of Seed
Very small and light – or their fruits have ‘wings’ or a ‘parachute’ to catch the wind.
Dandelions, maple seeds
Seeds can float for many hundreds of miles.
Seeds have hairs or hooks that catch in the animal’s fur. They may also be eaten, undigested and excreted somewhere else.
Strawberries, clover fruit
Capsules of the seed ‘explodes’ and shoots the seed further away from the mother plant.
That's the end of the topic!
Drafted by Joey (Biology)