Osmotic pressure is the pressure which needs to be applied to a solution to prevent the inward flow of water across a semipermeable membrane. It is also defined as the minimum pressure needed to nullify osmosis.
The phenomenon of osmotic pressure arises from the tendency of a pure solvent to move through a semi-permeable membrane and into a solution containing a solute to which the membrane is impermeable. This process is of vital importance in biology as the cell's membrane is selective toward many of the solutes found in living organisms.
In order to visualize this effect, imagine a U-shaped clear tube with equal amounts of water on each side, separated by a membrane at its base that is impermeable to sugar molecules (made from dialysis tubing). Sugar has been added to the water on one side. The height of the water on each side will change proportional to the pressure of the solutions.
Osmotic pressure causes the height of the water in the compartment containing the sugar to rise, due to movement of the pure water from the compartment without sugar into the compartment containing the sugar water. This process will stop once the pressures of the water and sugar water toward both sides of the membrane are equated. (See Osmosis).
Jacobus Henricus van 't Hoff first proposed a formula for calculating the osmotic pressure, but this was later improved upon by Harmon Northrop Morse.
Osmotic potential is the opposite of water potential, which is the degree to which a solvent tends to stay in a liquid.
Read more about Osmotic Pressure: Thermodynamic Explanation, Derivation of Osmotic Pressure, Morse Equation, Applications
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