GCSE Biology · Edexcel 1BI0 · Topic 6C
Plant hormones
Key points
- Plant hormones control growth and responses to the environment.
- Phototropism: shoots grow towards light. Auxin collects on the shaded side, where it makes cells elongate, so the shoot bends towards the light.
- Gravitropism (geotropism): shoots grow up and roots grow down. In roots, auxin slows growth on the lower side, so they bend downwards.
- Commercial uses of auxins: weedkillers (selective, affecting broad-leaved weeds), rooting powder for cuttings.
- Gibberellins are used to start seed germination and to grow bigger, seedless fruit.
- Ethene is used to control the ripening of fruit, so fruit can be picked unripe and ripened later in shops.
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Plants cannot move about, but they can grow towards light and water. They do this using plant hormones, chemicals that change how quickly cells grow in different parts of the plant. Humans have also found many commercial uses for these…
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