# A gardener places a potted plant on its side so that the shoot is horizontal. After several days, the shoot has curved upwards. Explain how auxins bring about this upward curvature of the shoot.

> Cambridge International IGCSE Biology (0610) — 14.5 Tropic responses · Explain · 4 marks

## Mark scheme (4 marks)

1. Auxins accumulate / move to the lower side of the horizontal shoot due to gravity
2. The higher concentration of auxins on the lower side causes greater cell elongation on the lower side
3. The upper side of the shoot has a lower concentration of auxins and so elongates less / grows more slowly
4. Unequal elongation / faster growth on the lower side causes the shoot to curve upwards — this is a positive gravitropism / the shoot shows negative gravitropism away from gravity

## Key terms

- [auxins](https://www.gradenine.co.uk/glossary/auxins)

## Related

- [Revision notes for Cambridge International IGCSE Biology (0610)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

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Source: [GradeNine](https://www.gradenine.co.uk/q/a-gardener-places-a-potted-plant-e068f68a) · Published by Druglandscape Ltd.