# A gardener notices that shoots of a climbing plant always grow towards the light coming through a window. Explain how the unequal distribution of auxin in the shoot brings about this response.

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

> The gardener observes that, over several days, the shoots consistently bend towards the window regardless of how the pot is turned.

## Mark scheme (5 marks)

1. Light causes auxin to move to / accumulate on the shaded side of the shoot
2. The shaded side therefore has a higher concentration of auxin than the illuminated side
3. Auxin promotes / stimulates cell elongation in the shoot
4. Cells on the shaded side elongate more / faster than cells on the illuminated side
5. This unequal elongation causes the shoot to bend / curve towards the light (phototropism)

## Key terms

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

## 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-gardener-notices-that-shoots-of-565a2161) · Published by Druglandscape Ltd.