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Osmosis is an important topic in biology because it provides the primary means by which water is transported into and out of cells.
Solutes, such as proteins or simple ions, dissolve in a solvent such as water. This raises the concentration of the solute in these areas. The solvent then diffuses to these areas of higher solute concentration to equalize the concentration of the solute throughout the solution.
A practical example of this osmosis in cells can be seen in red blood cells. These contain a high concentration of solutes including salts and protein. When the cells are placed in solution, water rushes in to the area of high solute concentration, bursting the cell.
Many plant cells do not burst in the same experiment. This is because the osmotic entry of water is opposed and eventually equalled by the pressure exerted by the cell wall, creating a steady state . In fact, osmotic pressure is the main cause of support in plant leaves.
When a plant cell is placed in a solution higher in solutes than inside the cell osmosis out of the cell occurs. The water in the cell moves to an area higher in solute concentration, and the cell shrinks and so becomes flaccid. This means the cell has become plasmolysed - the cell membrane has completely left the cell wall due to lack of water pressure on it.
In unusual environments, osmosis can be very harmful to organisms. For example, freshwater and saltwater aquarium fish placed in the other aquarium will die quickly, and in the case of saltwater fish rather dramatically. In addition, the use of table salt to kill leechArhynchobdellida Rhynchobdellida There is some dispute as to whether Hirudinea should be a class itself, or a subclass of the Clitellata. A leech is an annelid in the subclass Hirudinea . There are freshwater, terrestrial and marine leeches. Like their nees and slugFor other meanings see Slug (disambiguation Slugs are gastropods without or with very small shells, in contrast with snails from which they evolved, which have a prominent shell. Although they undergo torsion (twisting) during development, their bodies ars depends on osmosis.
When a solute is dissolved in a solvent, the random mixing of the two species results in an increase in the entropy of the system, which corresponds to a reduction in the chemical potential. For the case of an ideal solutionIn chemistry, an ideal solution is a solution where the enthalpy of solution is zero. The closer to zero the enthalpy of solution is, the more "ideally" the solution behaves. This becomes important in properties such as colligative properties, where the c the reduction in chemical potential corresponds to:
where is the ideal gas constant, is the temperature and is the solute concentration in terms of mole fractionThe Mole fraction is one way of expressing the relative concentration of a given species. The Mole fraction ''x of species i is defined as the number of moles of i divided by the total number of moles in the system: x n ''N where n is the number of moles. Most real solutions approximate ideal behavior for low solute concentrations (At higher concentrations interactions between solute and solvent cause deviations from Equation 1). This reduced potential creates a driving force and it is this force which drives diffusion of water through the semipermeable membrane.