# A student places a piece of potato tissue into a concentrated sugar solution and leaves it for 30 minutes. When removed, the potato tissue is noticeably smaller and has become flaccid. Explain why the potato tissue changed in this way.

> Eduqas A-Level Biology — 1.3 Cell membranes and transport · Explain · 5 marks

> Potato cells contain a vacuole filled with cell sap. The cell membrane acts as a selectively permeable barrier. When potato tissue is placed in a concentrated sugar solution, water moves across the cell membrane.

## Mark scheme (5 marks)

1. The concentrated sugar solution has a lower water concentration than the cell sap inside the potato cells
2. Water moves out of the potato cells by osmosis
3. Osmosis is the movement of water molecules from a region of higher water concentration to a region of lower water concentration
4. The vacuole loses water / the cell contents shrink away from the cell wall (the cell becomes plasmolysed)
5. This loss of water causes the tissue to decrease in size / become flaccid because the cells no longer have turgor pressure supporting them

## Related

- [Revision notes for Eduqas A-Level Biology](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
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Source: [GradeNine](https://www.gradenine.co.uk/q/a-student-places-a-piece-of-3255bea8) · Published by Druglandscape Ltd.