This membrane is like a sieve, allowing solvent molecules, which are small, to pass through it, but preventing larger molecules dissolved in the solvent from passing through. If a selectively permeable membrane separates two solutions of different concentrations, solvent molecules pass through the membrane from the side of lesser concentration to the side of greater concentration. This tends to equalize the concentrations on either side of the membrane. Cells and bacteria can be ruptured, for experimental purposes, by osmotic shock. For example, if red blood cells, which are normally found in blood plasma, are placed in pure water, then the cell walls allow the water to diffuse inwards, and the cells swell and eventually burst.
Osmosis is of great importance in many processes that occur in animals and plants.
It controls the intake of water by the hairs on plant roots, and the production of urine in the kidney. The turgidity of plant cells is due to their maintaining a difference in pressure across their cell walls. Water enters their concentrated cell contents and effectively 'inflates' the cell. 1. membrane Dictionary of Biology, Oxford University Press 2. membrane A Dictionary of Science, Oxford University Press 3. 4. membrane The Penguin Dictionary of Psychology 5.