If a dilute solution is separated from a concentrated solution by a partially permeable membrane, water diffuses across the membrane from the dilute to the concentrated solution. This is known as osmosis. A partially permeable membrane is porous but allows water to pass through more rapidly than dissolved substances. Since a dilute solution contains, in effect, more water molecules than a concentrated solution, there is a diffusion gradient which favours the passage of water from the dilute solution to the concentrated solution. In living cells, the cell membrane is partially permeable and the cytoplasm and vacuole (in plant cells) contain dissolved substances. As a consequence, water tends to diffuse into…