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Osmosis

Osmosis is diffusion of water through a membrane that lets water through but holds back dissolved substance. The water goes to where the concentration of dissolved substance is highest, that is where the water concentration is lowest. If you put a cell in very salty water, water leaves and the cell shrinks. In pure water an animal cell can take up so much water that it bursts. The plant cell tolerates it better, because the cell wall stops the swelling. Osmosis does not need ATP.

water→higher concentration of solute\text{water} \rightarrow \text{higher concentration of solute}the direction in osmosis

Symbols

membranemembranelets water through

Example

A cell in very salty water loses water and shrinks.

In pure water it takes up water.

Always compare the concentration outside with the one inside, not only with "a lot" or "a little" salt.
Practise the cell for free →

← The cell membrane · A cross of Aa with Aa →

Part of Biology 1: The cell.