Why does osmosis stop at equilibrium?
Osmosis appears to stop at equilibrium because the water potential (concentration of free water) is equal on both sides, so there is no NET movement of water.
GCSE Biology
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
In more detail
Osmosis is the net movement of water from a region of higher water potential (more dilute) to lower water potential (more concentrated) across a partially permeable membrane. Water molecules keep moving both ways all the time, but once both sides have the same water potential, water crosses in each direction at equal rates — so there is no net movement, and the volumes stay the same.
Key points for the exam
- Equilibrium = equal water potential on both sides.
- Water still moves both ways, but at equal rates → no NET movement.
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