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This lesson covers plant hormones and their roles in controlling plant growth and development. This is Higher Tier content on the AQA GCSE Biology specification. It includes the Required Practical on investigating the effect of light on seedling growth, which demonstrates phototropism.
Unlike animals, plants cannot move to respond to changes in their environment. Instead, they grow towards or away from stimuli. These directional growth responses are called tropisms.
| Tropism | Stimulus | Positive Response (towards) | Negative Response (away from) |
|---|---|---|---|
| Phototropism | Light | Shoots grow towards light | Roots grow away from light |
| Gravitropism (geotropism) | Gravity | Roots grow towards gravity (downwards) | Shoots grow away from gravity (upwards) |
| Hydrotropism | Water/moisture | Roots grow towards water | — |
| Thigmotropism | Touch | Tendrils of climbing plants wrap around supports | — |
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