Passive process which does not require the cell to expend energy. It is the potential energy stored in a concentration gradient that drives diffusion. Rate of diffusion is regulated by the permeability of the membrane, so some molecules diffuse more freely than others.
Water diffuses freely across most cell membranes.
A solution with a greater solute concentration than that inside a cell. A solution with a lower solute concentration compared to that inside a cell. A solution with an equal solute concentration compared to that inside a cell. Water diffuses down its concentration gradient. Some solute molecules can reduce the proportion of water molecules that can freely diffuse.