GCSE Biology · AQA 8461 · Topic 4.5.4
Plant hormones
Key points
- Plants grow towards light (phototropism) and respond to gravity (gravitropism or geotropism): shoots grow up, roots grow down.
- Auxin is made in the tips. It moves to the shaded side of a shoot, making those cells elongate so the shoot bends towards the light.
- In roots, auxin collects on the lower side and slows growth there, so the root bends downwards.
- Gibberellins start seed germination; ethene controls cell division and fruit ripening.
- Uses: auxins as weedkillers and rooting powders and in tissue culture; ethene to ripen fruit during transport; gibberellins to end dormancy and make bigger fruit.
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Plants cannot move to find light or water, but they can control the direction they grow. This sub-topic explains how plant hormones produce these responses and how people use the hormones in farming and horticulture.
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