Osmosis and Diffusion


Cells are able to gain or lose water by the process of osmosis. The rate at which cells gains or loses water depends on the water concentration of the solution outside the cell compared to the water concentration of the solution inside the cell. 

Osmosis is the net movement from a high water concentration of water to a low water concentration of water across a semi-permeable membrane.

A semi-permeable membrane only lets molecules of a specific size pass through it.


Molecules can move in or out of cells by the process of diffusion.


Diffusion is the net movement of molecules from a high concentration of molecules to a low concentration of molecules. This is caused by the random movement of molecules.

The difference in the concentration of fo a substance between two areas is called the concentration gradient. The greater difference, the steeper the concentration gradient is, therefore the faster the molecules in a substance will diffuse.

Diffusion stops occurring when the concentration gradient is level and the molecules are moving equally in all directions.

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