Definition of Osmotic Pressure or Osmotic Potential

Definition of osmotic pressure or osmotic potential (O.P.):

Osmotic pressure is the amount of pressure that needs to be applied to a solution to prevent water from moving into it through a semi-permeable membrane that separates it from pure water.

Osmotic pressure is usually represented by the symbol π’

The osmotic potential of a solution is the difference between the water potential of pure water and the water potential of the solution.

To make the water potential of the solution equal to that of pure water, an extra pressure has to be applied to the solution.

One unit of pressure is one atmosphere (atm), which is equivalent to 1.01 bars or 0.987 atm in the S.I. system of units.

Here is a possible way to rewrite the explanation of osmotic pressure and osmotic potential:

Osmotic pressure is not a real pressure, but a measure of how much a solution tends to draw water into it through a semi-permeable membrane that separates it from pure water.

Osmotic pressure is usually denoted by the symbol π’ Modern physiologists prefer to use the term osmotic potential, which is the component of water potential that depends on the concentration of solutes in the solution.

Osmotic potential is negative, meaning that it reduces the water potential of the solution.

The more solutes are added to the solution, the more negative the osmotic potential becomes.

In a pure solvent, the osmotic potential is zero, which is the highest possible value.

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