What is osmosis?

Osmosis is the passive diffusion of water, which therefore, doesn't require any energy to occur. Typically water will move from an area of high concentration to an area of low concentration across a semi-permeable membrane.For example. If the solute (I.E salt) content of a cell was higher than that of the blood, water from the blood would diffuse into the cell itself via its cell membrane which is semi-permeable. Which then increases the amount of water in the cell and decreases the concentration of the solute.As a result if water enters a cell it can cause it to increase in size (it will eventually burst though if too much water enters), but the opposite can happen if water leaves the cell (it will shrink).