BRAINCAKEWater Potential ψ
Water potential, symbol ψ (the Greek letter psi), is a measure of the tendency of water molecules to move out of a solution. It depends on how many free water molecules there are and how much pressure is acting on the water. It is measured in units of pressure, usually kilopascals (kPa).
By definition, pure water at atmospheric pressure has a water potential of 0 kPa. This is the highest possible water potential at atmospheric pressure.
When a solute such as sucrose or salt dissolves in water, water molecules cluster around the solute particles. Fewer water molecules are free to move, so the water potential falls below zero: it becomes negative. The more concentrated the solution, the more negative its water potential.
Sign in free to see the rest of this lesson, the R.E.C.I.P.E. recall steps and the quiz
BrainCake is free. Make an account in seconds and pick up where this page stops.
More in Cell Transport Mechanisms
- Transport Across the Cell Membrane
- Passive and Active Transport
- Diffusion
- Facilitated Diffusion
- Osmosis
- Modelling Osmosis
- Osmotic Concentrations
- Osmosis in Animal Cells
All 18 lessons in Cell Transport Mechanisms · All Edexcel AS-level Biology topics