osmosis

'''Definition'''

''noun''

1. [[Diffusion]] of a [[solvent]] (usually [[water]] molecules) through a [[semipermeable membrane]] from an area of low [[solute]] [[concentration]] to an area of high [[solute]] [[concentration]].

2. [[Net]] [[movement]] of [[water]] molecules through a [[semipermeable membrane]] from an area of higher [[water potential]] to an area of lower [[water potential]].

3. Tendency of [[water]] to [[flow]] from a [[hypotonic]] [[solution]] (low [[concentration]] of [[dissolved]] substances) to [[hypertonic]] [[solution]] (higher [[concentration]] of dissolved substances) across a [[semipermeable membrane]]


'''Supplement'''

In biological systems, osmosis is essential since many biological membranes are [[semipermeable]], and it leads to different [[physiological]] effects. For example, when an [[animal cell]] is exposed to a [[hypertonic]] surrounding (or lower water concentration) the water will leave the [[cell]] causing the [[cell]] to [[shrink]].

When an [[animal cell]] is placed in a [[hypotonic]] surrounding (or higher water concentration), the [[water]] molecules will move into the [[cell]] causing the [[cell]] to swell. If osmosis continues and becomes excessive the cell will eventually burst. In a [[plant cell]], [[excessive]] osmosis is prevented due to the [[osmotic pressure]] exerted by the [[cell wall]] thereby stabilizing the [[cell]]. In fact, [[osmotic pressure]] is the main cause of support in [[plants]]. However, if a plant cell is placed in a [[hypertonic]] surrounding, the [[cell wall]] cannot prevent the cell from losing [[water]]. It results in cell shrinking (or cell becoming [[flaccid]]).


Word origin: Latinized form of now obsolete ''osmose''.

Related forms: osmotically (adverb), osmotic (adjective).

See also: [[diffusion]], [[plasma membrane]], [[water]], [[osmotic pressure]], [[solution]].