Adhesion of Water to Polar or Charged Materials
Definition
Adhesion
The attraction between water molecules and other surfaces, enabling water to cling to them and move against gravity.
- Water is polar (covered in the A1.1.3), meaning it's attracted to other polar or charged materials.
- This attraction allows water to "stick" to surfaces and move along them.
- Key difference from cohesion:
- Cohesion = water molecules attracted to each other
- Adhesion = water molecules attracted to other polar or charged surfaces.
Capillary Action: Adhesion and Cohesion Working Together
Definition
Capillary action
Capillary action refers to the movement of water through narrow spaces, even against gravity.
- It requires both adhesion and cohesion where:
- Adhesion pulls water up along the walls of narrow spaces.
- Cohesion (hydrogen bonds between water molecules) pulls the rest of the water column along.
- This results in water moving upward through small tubes or pores without external energy input.
Capillary Action in Soil
- In soil, water occupies the spaces between particles, moving through pores of varying sizes.
- Porous soils, such as those rich in sand or silt, have numerous small spaces that allow water to rise through capillary action.
- When the soil is dry, water is drawn upward from deeper layers or underground sources, rehydrating the upper layers.
- This matters for organisms because it aids:
- Water distribution: Capillary action redistributes water throughout the soil profile, making it accessible to plant roots even when the surface is dry.
- Survival in arid conditions: In dry environments, capillary action draws water from deeper soil layers upward, helping plants access moisture.
