osmosis

The process by which solvent tends to move through a semipermeable membrane from a solution of lower to a solution of higher osmolal concentration of the solutes to which the membrane is relatively impermeable. [G. osmos, a thrusting, an impulsion]

- reverse o. movement of solvent in the opposite direction from o., i.e., pressure filtration of solvent through a semipermeable membrane that will hold back the solutes; commonly replaced by filtration or ultrafiltration when speaking of capillary membranes, as in the renal glomerulus.

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os·mo·sis äz-'mō-səs, äs- n, pl os·mo·ses -.sēz movement of a solvent through a semipermeable membrane (as of a living cell) into a solution of higher solute concentration that tends to equalize the concentrations of solute on the two sides of the membrane

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n.

the passage of a solvent from a less concentrated to a more concentrated solution through a semipermeable membrane. This tends to equalize the concentrations of the two solutions. In living organisms the solvent is water and cell membranes function as semipermeable membranes, and the process of osmosis plays an important role in controlling the distribution of water. The osmotic pressure of a solution is the pressure by which water is drawn into it through the semipermeable membrane; the more concentrated the solution (i.e. the more solute molecules it contains), the greater its osmotic pressure.

• osmotic adj.

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os·mo·sis (oz-moґsis) (os-moґsis) [Gr. ōsmos impulsion] the diffusion of pure solvent across a membrane in response to a concentration gradient, usually from a solution of lesser to one of greater solute concentration. osmotic adj