Osmotic pressure 31383 223983407 2008-07-06T20:36:16Z 98.197.21.91 [[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 &middot; atm &middot; mol<sup>-1</sup> &middot; 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]]