# Explain how auxins cause a seedling root to grow downwards in response to gravity.

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

> A seedling is germinated in complete darkness so that only the effect of gravity influences its growth. The root grows downwards into the soil.

## Mark scheme (4 marks)

1. Auxins move towards the lower side of the root in response to gravity
2. Higher concentration of auxin on the lower side inhibits / reduces cell elongation in the root
3. Cells on the upper side elongate more / faster than cells on the lower side
4. Unequal elongation causes the root to bend / curve downwards, which is a positive gravitropism

## 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)
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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-how-auxins-cause-a-seedling-c33c44bb) · Published by Druglandscape Ltd.