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Tonicity is a measure of effective osmolarity or effective osmolality. Osmolality and osmolarity are properties of a particular solution, independent of any membrane. Tonicity is a property of a solution in reference to a particular membrane, and is equal to the sum of the concentrations of the solutes which have the capacity to exert an osmotic force across that membrane. Tonicity, also, depends on solute permeability.(Permeant solutes: Do not affect tonicity. Impermeant solutes: Do affect tonicity.) Image File history File links Information. ... When substances are dissolved, the number of distinct particles in solution is measured as Osmolality. ... Osmolality, in biology and chemistry, is a measure of moles of solute per kg of water. ...

Hypertonic, hypotonic and isotonic solutions are defined in reference to a cell membrane by comparing the tonicity of the solution with the tonicity within the cell. This article does not cite any references or sources. ... This article does not cite any references or sources. ... This article or section does not adequately cite its references or sources. ...

• If a cell is placed in a hypotonic solution (one of lower tonicity than the cell contents), the water concentration is greater outside the cell and so osmosis produces a net movement of water into the cell. This causes animal cells (without a cell wall) to burst and plant cells (which do have a cell wall) to become turgid.
• If the medium is isotonic, the water concentration is the same on either side of the cell membrane, and there is no net movement of water.
• If the medium is hypertonic, the water concentration inside the cell is greater. This leads to net movement of water out of the cell. Animal cells shrivel up; plant cells become plasmolysed (the cell membrane pulls away from the cell wall in places as the cytoplasm shrinks).

The effects of tonicity on animal cells and plant cells differ, since plants cells have a cell wall that does not change shape. Osmosis is the net movement of water across a partially permeable membrane from a region of high solvent potential to an area of low solvent potential, up a solute concentration gradient. ...

Tonicity is also applied to the elastic tension of living muscles, arteries, etc. that facilitates response to stimuli. Clinically, this is referred to as tonus (See muscle tone). Bodybuilder showing highly developed muscle tone. ...

References

• Osmosis
• Fluid Physiology

Tonicity refers to the total concentration of non-permeating solute particles in a solution. eg. a 300mmol/l solution of urea is isoosmotic to red blood cells because its osmolarity is the same as that of red blood cells, but it is hypotonic to red blood cells because urea is able to cross the cell membrane and so the total concentration of non-permeating particles = 0

See also

• Osmosis
• Osmole (unit)