Osmosis is a special type of diffusion in which water is diffused across the membrane relatively freely to maintain a balance in the concentration of water on each side of the membrane. When talking about osmosis it is important to understand tonicity. This is how the solution affects the volume of the cell. An isotonic solution is a solution in which the concentration of solutes inside the cell is equal to the concentration outside the cell. A hypertonic solution is a solution in which the concentration of solutes inside the cell is lower than the concentration of solutes outside the cell. This would cause the cell to shrink. A hypotonic solution is a solution in which the concentration of solutes inside the cell is greater than the concentration of solutes outside the cell. This would cause the cell to burst (Wood,