Osmosis

For other uses, see Osmosis (disambiguation).

The process of osmosis over a semipermeable membrane. The blue dots represent particles driving the osmotic gradient.

Osmosis (/ɒzˈmoʊsɪs/, US also /ɒs-/)[1] is the spontaneous net movement or diffusion of solvent molecules through a selectively-permeable membrane from a region of high water potential (region of lower solute concentration) to a region of low water potential (region of higher solute concentration),[2] in the direction that tends to equalize the solute concentrations on the two sides.[3][4][5] It may also be used to describe a physical process in which any solvent moves across a selectively permeable membrane (permeable to the solvent, but not the solute) separating two solutions of different concentrations.[6][7] Osmosis can be made to do work.[8] Osmotic pressure is defined as the external pressure required to prevent net movement of solvent across the membrane. Osmotic pressure is a colligative property, meaning that the osmotic pressure depends on the molar concentration of the solute but not on its identity.

Osmosis is a vital process in biological systems, as biological membranes are semipermeable. In general, these membranes are impermeable to large and polar molecules, such as ions, proteins, and polysaccharides, while being permeable to non-polar or hydrophobic molecules like lipids as well as to small molecules like oxygen, carbon dioxide, nitrogen, and nitric oxide. Permeability depends on solubility, charge, or chemistry, as well as solute size. Water molecules travel through the plasma membrane, tonoplast membrane (vacuole) or organelle membranes by diffusing across the phospholipid bilayer via aquaporins (small transmembrane proteins similar to those responsible for facilitated diffusion and ion channels). Osmosis provides the primary means by which water is transported into and out of cells. The turgor pressure of a cell is largely maintained by osmosis across the cell membrane between the cell interior and its relatively hypotonic environment.

  1. ^ Jones, Daniel (2011). Roach, Peter; Setter, Jane; Esling, John (eds.). Cambridge English Pronouncing Dictionary (18th ed.). Cambridge University Press. ISBN 978-0-521-15255-6.
  2. ^ "Osmosis | A Level Notes".
  3. ^ "Osmosis". Oxford English Dictionary (Online ed.). Oxford University Press. (Subscription or participating institution membership required.)
  4. ^ Osmosis, Encyclopædia Britannica on-line
  5. ^ Haynie, Donald T. (2001). Biological Thermodynamics. Cambridge: Cambridge University Press. pp. 130–136. ISBN 978-0-521-79549-4.
  6. ^ Waugh, A.; Grant, A. (2007). Anatomy and Physiology in Health and Illness. Edinburgh: Elsevier. pp. 25–26. ISBN 978-0-443-10101-4.
  7. ^ Osmosis Archived 22 February 2008 at the Wayback Machine. University of Hamburg. last change: 31 July 2003
  8. ^ "Statkraft to build the world's first prototype osmotic power plant". Statkraft. 3 October 2007. Archived from the original on 27 February 2009.