Turgor (also called turgor pressure or osmotic pressure) is the pressure that can build in a space that is enclosed by a membrane that is permeable to a solvent such as water but not to solutes.

A biological cell, for example a plant cell, contains ions, sugars, amino acids, and other substances. In a hypotonic environment, water flows across the plasma membrane into the cell (since the concentration of water is lower inside the cell than outside), causing it to expand. The cell wall of a plant cell restricts the expansion, causing the cell to press against the wall. The resulting pressure is called turgor.

The osmotic pressure π of a dilute solution can be calculated using the formula

where

M is the molarity

R is the molar gas constant

T is absolute temperature (i.e. measured in kelvin).

Note the similarity of the above formula to the ideal gas law.

See also

• Pfeffer cell
• cell wall