Osmotic pressure
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2008-07-06T20:36:16Z
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[[Image:Osmotic pressure on blood cells diagram.svg|thumb|250px|Osmotic pressure on red blood cells]]
'''Osmotic pressure''' is the [[Fluid statics|hydrostatic]] [[pressure]] produced by a solution in a space divided by a [[differentially permeable membrane|semipermeable membrane]] due to a differential in the concentrations of solute. [[Osmoregulation]] is the [[homeostasis]] mechanism of an organism to reach balance in osmotic pressure.
'''Osmotic potential''' is the opposite of [[water potential]] with the former meaning the degree to which a solvent (usually water) would want to stay in a liquid.
*[[Tonicity#Hypertonicity|Hypertonicity]] is a solution that causes cells to shrink. It may or may not have a higher osmotic pressure than the cell interior since the rate of water entry will depend upon the permeability of the cell membrane.
*[[Tonicity#Hypotonicity|Hypotonicity]] is a solution that causes cells to swell. It may or may not have a lower osmotic pressure than the cell interior.since the rate of water entry will depend upon the permeability of the cell membrane.
*[[Tonicity#Isotonicity|Isotonic]] is a solution that produces no change in cell volume.
When a [[biological tissue|biological]] [[cell (biology)|cell]] is in a hypotonic environment, the cell interior accumulates [[water]], water flows across the [[cell membrane]] into the cell, causing it to expand. In [[plant cell]]s, the [[cell wall]] restricts the expansion, resulting in pressure on the cell wall from within called [[turgor pressure]]. The osmotic pressure π of a dilute solution can be calculated using the formula
:<math> P = i\cdot M\cdot R\cdot T</math>,
where
:''i'' is the [[van 't Hoff factor]]
:''M'' is the [[molarity]]
:''R'' is the [[gas constant]], where ''R'' = 0.08206 L · atm · mol<sup>-1</sup> · K<sup>-1</sup>
:''T'' is the [[thermodynamic temperature]] (formerly called absolute temperature)
Note the similarity of the above formula to the [[ideal gas law]] and also that osmotic pressure is not dependent on particle charge. This equation was derived by [[van 't Hoff]].
== Applications ==
Osmotic pressure is the basis of [[reverse osmosis]], a process commonly used to purify water. The water to be purified is placed in a chamber and put under an amount of pressure greater than the osmotic pressure exerted by the water and the solutes dissolved in it. Part of the chamber opens to a differentially permeable membrane that lets water molecules through, but not the solute particles. The osmotic pressure of ocean water is about 27 [[Atmosphere (unit)|atm]]. Reverse osmosis [[desalination|desalinator]]s use pressures around 70 atm to produce fresh water from [[seawater|ocean salt water]].
Osmotic pressure is necessary for many plant functions. It is the resulting [[turgor pressure]] on the cell wall that allows [[herbaceous plant]]s to stand upright, and how plants regulate the aperture of their [[stomata]]. In animal cells which lack a cell wall however, excessive osmotic pressure can result in [[cytolysis]].
* [[Cell wall]]
* [[Cytolysis]]
* [[Gibbs-Donnan effect]]
* [[Osmosis]]
* [[Pfeffer cell]]
* [[Plasmolysis]]
* [[Turgor pressure]]
For the calculation of molecular weight by using colligative properties, osmotic pressure is the most preferred property.
===Potential osmotic pressure===
Potential osmotic pressure is the maximum osmotic pressure that could develop in a solution if it were separated from distilled water by a selectively permeable membrane. It is the number of solute particles in a unit volume of the solution that directly determines its potential osmotic pressure. If one waits for equilibrium, osmotic pressure reaches potential osmotic pressure.
== External links ==
* [http://www.bbc.co.uk/dna/h2g2/A686766 Osmotic pressure and potential]
* [http://www.biologie.uni-hamburg.de/b-online/e22/22c.htm Osmotic pressure]
[[Category:Cell biology]]
[[Category:Membrane biology]]
[[cs:Osmotický tlak]]
[[de:Turgor]]
[[es:Presión osmótica]]
[[is:Osmótískur þrýstingur]]
[[it:Pressione osmotica]]
[[fr:Osmose]]
[[he:לחץ אוסמוטי]]
[[mk:Осмотски притисок]]
[[nl:Osmotische druk]]
[[ja:浸透圧]]
[[ka:ოსმოსური წნევა]]
[[nn:osmotisk trykk]]
[[pl:Ciśnienie osmotyczne]]
[[pt:Pressão osmótica]]
[[ru:Осмотическое давление]]
[[sk:Osmotický tlak]]
[[fi:Osmoottinen paine]]
[[tr:Osmotik basınç]]
[[uk:Осмотичний тиск]]
[[zh:滲透壓]]