The net movement of a substance down a concentration gradient. Diffusion of a substance across a biological membrane. Spontaneous process which is a function of a concentration gradient when a substance is more concentrated on one side of the membrane. Passive process which does not require the cell to expend energy. 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.
Osmosis is the passive transport of water Animal cells are not tolerant of excessive osmotic uptake or loss of water. 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. In an isotonic environment, the volume of an animal cell will remain stable with no net movement of water across the plasma membrane.