Tropism
Exam-ready definition
A growth response of a plant in which the direction of growth is determined by the direction of the stimulus. Phototropism responds to light, gravitropism to gravity.
How this is marked
The word 'growth' must appear. Tropisms are growth responses, not movements. The Extended explanation uses auxin: it accumulates on the shaded side of a shoot, that side elongates faster, and the shoot bends toward the light.
In an exam answer
Explaining a shoot bending to light: 'Auxin gathers on the shaded side, which grows faster, so the shoot bends towards the light. A positive phototropism.'
Full topic guide: Coordination & response
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