# Explain how the cohesive and adhesive properties of water contribute to the transport of water through the xylem of a plant.

> IB DP Biology Standard Level (2023 syllabus) — A1.1 Water · Explain · 4 marks

## Mark scheme (4 marks)

1. Cohesion arises because hydrogen bonds form between adjacent water molecules, causing them to stick together.
2. Cohesion allows water molecules to form a continuous, unbroken column within the xylem vessel, so tension created by transpiration at the leaf surface pulls the entire column upward.
3. Adhesion occurs because hydrogen bonds form between water molecules and the hydrophilic cellulose walls of the xylem, causing water to stick to the walls.
4. Adhesion helps counteract gravity by allowing water to cling to the xylem walls, reducing the tendency of the water column to fall and supporting capillary action.

## Key terms

- [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)
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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-how-the-cohesive-and-adhesive-f9100def) · Published by Druglandscape Ltd.