Facilitated Active Transport See diagram that compares all three types of diffusion . Passive Diffusion Simple diffusion is the movement of a substance from a place of high concentration to one of lower concentration. Here is a sample diagram of diffusion across a membrane. A special case of passive transport occurs with osmosis .
Osmosis is the diffusion of water across a selectively permeable membrane.
A spontaneous transport of solvent occurs from a dilute solute or salt solution to a concentrated solute or salt solution across a semipermeable membrane which allows the passage of the solvent but impedes passage of the salt solutes. This is very important with cells. All cells have some amount of dissolved salts,proteins and such, the flow of water across the plasma membrane depends upon the concentraton of water in the liquid that the cells are in. In humans the concentrations are equal inside and outside the cell. Therefore, water will neither enter or exit the cell.