# Explain what happens to the water potential and volume of a flaccid plant cell when it is placed in pure water, until equilibrium is reached.

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

## Mark scheme (4 marks)

1. Pure water has a water potential of zero, which is higher than the water potential of the flaccid cell (which is negative due to dissolved solutes).
2. Water moves by osmosis into the cell down the water potential gradient (from pure water into the cell).
3. As water enters, the cell vacuole expands / the cell increases in volume and the cell wall is stretched, generating a pressure potential / turgor pressure.
4. Equilibrium is reached when the water potential of the cell equals zero (equals that of pure water) / when the rising pressure potential fully offsets the solute potential, so there is no net movement of water.

## Key terms

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

## Related

- [Revision notes for IB DP Biology Standard 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-what-happens-to-the-water-af7e25e9) · Published by Druglandscape Ltd.