# A scientist discovered that when the growing tip of a young plant shoot is removed, the shoot stops bending towards light. When the tip is replaced, the shoot bends towards light again. Explain how the shoot normally bends towards light, including the role of auxin.

> Pearson Edexcel A-Level Biology A (9BI0) — 4.7 Plant responses · Explain · 5 marks

> Auxin is a plant hormone produced in the tip of a shoot. It controls the rate of cell elongation in the shoot. Auxin moves away from the light source, accumulating on the shaded side of the shoot.

## Mark scheme (5 marks)

1. Auxin is produced in the tip of the shoot
2. Auxin moves towards / accumulates on the shaded side of the shoot
3. Auxin causes cells to elongate / grow longer
4. Cells on the shaded side elongate more than cells on the light side
5. This unequal growth causes the shoot to bend towards the light (phototropism)

## Key terms

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

## Related

- [Revision notes for Pearson Edexcel A-Level Biology A (9BI0)](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-scientist-discovered-that-when-the-d4c26b25) · Published by Druglandscape Ltd.