# Explain why a plant seedling placed on its side will, over time, have its shoot growing upwards and its root growing downwards.

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

> A gardener places a newly germinated seedling horizontally in a pot of soil and leaves it for several days in the dark.

## Mark scheme (4 marks)

1. Auxin moves to / accumulates on the lower side of both the shoot and the root
2. In the shoot, the higher concentration of auxin on the lower side causes greater / faster cell elongation on the lower side
3. Greater elongation on the lower side causes the shoot tip to bend / curve upwards (away from gravity / negative gravitropism)
4. In the root, the higher concentration of auxin on the lower side inhibits cell elongation on that side, so the upper side elongates more, causing the root to bend / curve downwards (towards gravity / positive gravitropism)

## Related

- [Revision notes for Pearson Edexcel International GCSE Biology (4BI1)](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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