# Explain how osmosis causes a plant cell to become turgid when placed in a hypotonic solution.

> IB DP Biology Higher Level (2023 syllabus) — B2.1 Membranes and membrane transport · Explain · 4 marks

## Mark scheme (4 marks)

1. Water moves by osmosis from the hypotonic solution (higher water potential) into the cell (lower water potential) across the partially/selectively permeable membrane.
2. The vacuole enlarges as it absorbs water, increasing the volume of the cell and pushing the cytoplasm against the cell wall.
3. The inextensible (rigid) cell wall generates a pressure potential (turgor pressure / wall pressure) that opposes further entry of water.
4. Equilibrium is reached when the water potential inside the cell equals that of the external solution (i.e. when pressure potential balances the solute/osmotic potential), at which point the cell is fully turgid and net water movement ceases.

## Key terms

- [osmosis](https://www.gradenine.co.uk/glossary/osmosis)
- [hypotonic solution](https://www.gradenine.co.uk/glossary/hypotonic-solution)

## 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-osmosis-causes-a-plant-eaf0a6e5) · Published by Druglandscape Ltd.