29 August 2006


Osmosis is a colligative property of solutions where when two solutions of different concentrations are separated by a semi permeable membrane, a diffusion of the solvent molecules is observed from a region of lower solute concentration to a region of higher solute concentration.

A colligative property of solution is the one that does not depend on the properties of the solute, but just the physical concentration.

The amount of pressure that needs to be applied on the solution of higher concentration to prevent the solvent molecules from moving in through the membrane is called the turgor pressure. So, iteratively, a pressure applied on a solution of higher concentration to a limit exceeding the turgor pressure results in the solvent molecules moving from a level of higher concentration to that of lower concentration. This phenomenon is called reverse osmosis.

Osmosis is observed in real life: ascent of sap, shrinking of potatoes dipped in salt solution, transit of water through the tissues in animals etc.

While osmosis can be useful for many biological activities, it is quite catastrophical for a few creatures. Fresh water fish that get dumped into the sea die almost immediately owing to an osmotic gradient between their tissues and the surrounding water.

The phenomena of osmosis and reverse osmosis are used in many medical and industrial applications such as dialysis, desalination of sea water, water purification etc.

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