IB Biology A1.1.4 Adhesion of water
Adhesion attracts water to other polar or charged surfaces, supporting capillary movement through narrow spaces such as soil pores and plant tissues.
- Syllabus
- First assessment 2025
- Objective
- ib_null_biology_001_001_004
- Level
- All levels
Quick summary
Adhesion is the attraction between water molecules and a different material. Because water is polar, its partial charges can interact with charged or polar groups on surfaces such as soil particles, glass and plant cell walls. In a narrow space, adhesion draws water along the surface while cohesion keeps neighbouring water molecules connected. Together these interactions contribute to capillary action and can help water move through small pores and tubes. Adhesion must be distinguished from cohesion: cohesion is water-to-water attraction, whereas adhesion is water-to-surface attraction. The available exam evidence for this objective is limited, so students should prioritise this precise distinction and its consequence rather than memorising a broad list of examples. A complete answer identifies the different surface involved and links the attraction to capillary movement.
Concept visual
One diagram for the relationship students need to remember.
Common mistakes
Using adhesion and cohesion as interchangeable terms.
Describing adhesion as attraction only between water molecules.
Attributing capillary action to thermal or solvent properties.
Key takeaways
- Adhesion is attraction between water and another surface.
- Water adheres well to polar or charged materials.
- Adhesion and cohesion act together during capillary movement.
