Water crosses a semi-permeable membrane toward the side with more dissolved particles. The cell spends no energy on it.
What decides the direction?
Water follows the concentration gradient.
A higher solute concentration pulls water in.
Cells swell or shrink until both sides balance.
Solution | Effect on the cell |
|---|
Hypotonic | Swells |
Isotonic | No change |
Hypertonic | Shrinks |
DefinitionOsmosis is the net movement of water through a membrane toward a higher solute concentration.
Think of the membrane as a sieve that only lets water through.
ImportantRed blood cells burst when placed in pure water.
Plant cells in salty soil lose water, so the plant wilts.