# A scientist investigated the response of young bean plant shoots to gravity. The shoots were placed horizontally in the dark for 48 hours. After this time, the shoots had grown upward, away from the direction of gravity. Explain how auxin brings about this response in the shoots.

> Edexcel A-Level Biology A: Salters-Nuffield (9BN0) — 4.7 Plant responses · Explain · 5 marks

> A scientist investigated the response of young bean plant shoots to gravity. The shoots were placed horizontally in the dark for 48 hours. After this time, the shoots had grown upward, away from the direction of gravity.

## Mark scheme (5 marks)

1. Auxin is produced at the tip of the shoot
2. Auxin moves to / accumulates on the lower side of the horizontal shoot
3. Auxin causes cells to elongate / grow longer
4. Cells on the lower side elongate more than cells on the upper side
5. This unequal growth causes the shoot to bend / curve upward, away from gravity (negative gravitropism)

## Key terms

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

## Related

- [Revision notes for Edexcel A-Level Biology A: Salters-Nuffield (9BN0)](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-investigated-the-response-of-2ec5725f) · Published by Druglandscape Ltd.