# Explain how a shoot tip responds to light coming from one direction only.

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

> When light falls on a plant shoot from one side only, the shoot bends towards the light source. This response is controlled by a hormone produced in the shoot tip.

## Mark scheme (4 marks)

1. Auxin (is the hormone that) is produced in the shoot tip
2. Auxin moves to / accumulates on the shaded (darker) side of the shoot
3. The higher concentration of auxin on the shaded side causes cells on that side to elongate more
4. Unequal elongation causes the shoot to bend towards the light (positive phototropism)

## Key terms

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

## 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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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-how-a-shoot-tip-responds-6ebf6d2f) · Published by Druglandscape Ltd.