osmosis

Apachai · 03-25-2007, 01:29 PM

i know osmosis is the movement of water molecules from a low to a high concentration in plants (and therefore is passive transport). but does anyone know a more detailed description of theory of what osmosis actually is?

**lozoot** · 03-25-2007, 02:57 PM

Quote:

Osmosis is the net movement of a solvent across a semipermeable membrane from a region of high solvent potential to an area of low solvent potential.

It is a physical process in which a solvent moves, without input of energy, across a semipermeable membrane (permeable to the solvent, but not the solute) separating two solutions of different concentrations.[1] Osmosis releases energy, and can be made to do work, as when a growing tree-root splits a stone.

Net movement of solvent is from the less-concentrated (hypotonic), to the more-concentrated (hypertonic) solution, which tends to reduce the difference in concentrations. This effect can be countered by increasing the pressure of the hypertonic solution, with respect to the hypotonic. The osmotic pressure is defined to be the pressure (force per unit area) required to maintain an equilibrium, with no net movement of solvent. Osmotic pressure is a colligative property, meaning that the property depends on the concentration of the solute but not on its identity.

Osmosis is important in biological systems as many biological membranes are semipermeable. In general, these membranes are impermeable to organic solutes with large molecules, such as polysaccharides, while permeable to water and small, uncharged solutes. Permeability may depend on solubility properties, charge, or chemistry as well as solute size. Water molecules travel through the plasma cell membrane, tonoplast (vacuole) or protoplast in two ways. Either by diffusing across the phospholipid bilayer directly, or via aquaporins (small transmembrane proteins similar to those in faciliated diffusion and in creating 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.

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Apachai · 03-25-2007, 04:14 PM

Quote:

Originally Posted by lozootmaniac

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