An example of this behavior is the uptake of oxygen by a cell that is performing cellular respiration. Dissolved oxygen diffuses into a cell across a plasma membrane. As long as the oxygen is being consumed, diffusion into the cell will take place because the concentration gradient favors movement in that direction. This type of diffusion is called passive transport. 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.