# Explain how the water potential of red blood cells changes when they are placed in a hypertonic solution, and describe the consequences for cell structure.

> IB DP Biology Higher Level (2023 syllabus) — D2.3 Water potential · Explain · 4 marks

## Mark scheme (4 marks)

1. The hypertonic solution has a lower (more negative) water potential than the cytoplasm of the red blood cell.
2. Water moves out of the red blood cell by osmosis down the water potential gradient.
3. Loss of water reduces the volume of the cell, causing the cell membrane to shrink inward / the cell to crenate.
4. As water leaves, the solute concentration inside the cell increases, lowering the water potential of the cytoplasm until equilibrium is reached (water potentials equalise).

## Key terms

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

## Related

- [Revision notes for IB DP Biology Higher Level (2023 syllabus)](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/explain-how-the-water-potential-of-a000d54d) · Published by Druglandscape Ltd.