# Explain how differences in water potential between the soil, root hair cells, and the xylem drive the movement of water into a plant root.

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

> Plants absorb water from the soil through root hair cells. Water must travel from the soil solution, across the root cortex, and into the xylem vessels before it can be transported to the shoot.

## Mark scheme (4 marks)

1. Water potential of soil solution is higher (less negative) than the water potential of root hair cells
2. Water therefore moves by osmosis from the soil into root hair cells down a water potential gradient
3. Water uptake lowers the water potential of adjacent cortex cells relative to the root hair cells, so water continues to move inward across the cortex
4. Xylem has the lowest (most negative) water potential in the root, so water moves into the xylem by osmosis / down the water potential gradient

## Key terms

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

## 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-how-differences-in-water-potential-eb8ac6ab) · Published by Druglandscape Ltd.