16.3) Sexual reproduction in plants
- In the flower of most plants there are both stamen (male organs) and carpels (female organs), this is a condition known as bisexual or hermaphrodite.
- Some plants have unisexual flowers.
- Grasses have wind-pollinated flowers.
- They have small petals, and their stamens and stigmas hang outside the flower.
Pollination: is the transfer of pollen grains from the anther to the stigma.
Self-pollination: is the transfer of pollen grains from the anther of a flower to the stigma of the same flower, or a different flower on the same plant.
- No variation.
- Not be able to adapt to changing environmental conditions.
- No reliance on pollinators.
Cross-pollination: is the transfer of pollen grains from the anther of a flower to the stigma of a flower on a different plant of the same species.
- Guarantee variation.
- Better chance of adapting to changing conditions.
- Reliance on pollinators to carry the pollen to other plants.
- When a pollen grain lands on the stigma of a flower of the correct species, a pollen tube begins to grow.
- It grows down the style and into the ovary, where it enters a small hole, the micropyle, in an ovule.
- The nucleus of the pollen then passes along the pollen tube and fuses with the nucleus of the ovule.
- This process is called fertilisation.
Environmental conditions that affect germination of seeds:
Germination is a process, controlled by enzymes, in which the seed begins to develop into a new young plant. Three main factors are needed for successful germination.