# A student places a piece of potato tissue into a solution that has a lower water potential than the cytoplasm of the potato cells. Explain what happens to the potato cells over time.

> Edexcel A-Level Biology A: Salters-Nuffield (9BN0) — 1.6 Membranes and transport · Explain · 5 marks

> Potato cells contain a large central vacuole filled with cell sap. When potato tissue is placed in solutions of different water potentials, the cells can gain or lose water.

## Mark scheme (5 marks)

1. Water moves out of the potato cells (by osmosis)
2. Osmosis is the net movement of water molecules from a region of higher water potential to a region of lower water potential (through a partially permeable membrane)
3. The water potential of the external solution is lower than that of the cell cytoplasm / vacuole, so there is a net movement of water out of the cells
4. The vacuole and cytoplasm shrink / the cell becomes plasmolysed OR the cell membrane pulls away from the cell wall
5. The potato tissue becomes flaccid / soft / loses its firmness (because cells are no longer turgid)

## Key terms

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

## 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-student-places-a-piece-of-e3f71438) · Published by Druglandscape Ltd.