The movement of a solvent through a membrane separating two solutions of different concentrations. The solvent from the side of weaker concentration usually moves to the side of the stronger concentration, diluting it, until the concentrations of the solutions are equal on both sides of the membrane.
♦ The pressure exerted by the molecules of the solvent on the membrane they pass through is called osmotic pressure
. Osmotic pressure is the energy driving osmosis and is important for living organisms because it allows water and nutrients dissolved in water to pass through cell membranes.
left: The concentration of sugar molecules is greater on the right side of the membrane than on the left. The water molecules are small enough to move across the membrane, but the larger sugar molecules cannot pass through.
right: The water molecules move across the membrane until the water and sugar molecules are of equal concentration on both sides. This lowers the water level on the left side and raises it on the right side.