# Describe how auxin causes a plant root to respond to the force of gravity.

> Pearson Edexcel International GCSE Biology (4BI1) — 2.14 Coordination and response: flowering plants · Describe · 4 marks

> When a plant root is placed horizontally, it changes its direction of growth within a few hours so that it grows downwards into the soil.

## Mark scheme (4 marks)

1. Auxin moves to / accumulates on the lower side of the root (due to gravity)
2. Higher concentration of auxin on the lower side inhibits / slows cell elongation on that side
3. Lower concentration of auxin on the upper side allows / promotes greater cell elongation on that side
4. Unequal elongation causes the root to bend / grow downwards (positive gravitropism)

## Key terms

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

## Related

- [Revision notes for Pearson Edexcel International GCSE Biology (4BI1)](https://www.gradenine.co.uk/learn)
- [How to answer "Describe" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

---
Source: [GradeNine](https://www.gradenine.co.uk/q/describe-how-auxin-causes-a-plant-13884afd) · Published by Druglandscape Ltd.