Explain how auxin causes a plant shoot to grow towards light.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Plants can detect the direction of light and grow towards it. This response is controlled by a plant hormone called auxin.
Model answer (4 marks)
Auxin is produced at the tip of the shoot.
Auxin is transported down the shoot and accumulates on the shaded side.
Higher auxin concentration on the shaded side stimulates greater cell elongation there.
The unequal elongation bends the shoot so it curves towards the light.
Auxin is transported down the shoot and accumulates on the shaded side.
Higher auxin concentration on the shaded side stimulates greater cell elongation there.
The unequal elongation bends the shoot so it curves towards the light.
Examiner tips
- Use the exact sequence: production, transport, effect, result. Mention ‘shaded side’ to show understanding of phototropism. Show the cause–effect chain clearly.
Common mistakes
- Confusing light side with shaded side. Omitting the step that auxin causes cell elongation. Using vague terms like ‘growth’ instead of ‘cell elongation’.
Mark scheme (4 marks)
- Auxin is produced at the tip of the shoot
- Auxin moves to the shaded side of the shoot
- Auxin causes cells on the shaded side to elongate more
- Unequal elongation causes the shoot to bend/curve towards the light
Key terms in this question
Related
- All Eduqas GCSE Biology revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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