Osmotic pressure is a force that resists osmosis and is important in human biology and plant cell walls. It protects cells from dilution and helps plants maintain turgidity. The osmotic pressure equation is P = nRT/V.
Osmotic pressure is a volumetric force that resists the natural process of osmosis. It is most often referenced in human biology, where a living cell contains a concentrated solution of water and some other elements which it separates from external solutions by a semipermeable membrane. The natural process of osmosis tends to equalize the concentrations of solute materials in a solution by passing the solution through such membranes, and osmotic pressure is the amount of pressure a living cell exerts to resist this force. This pressure protects the internal components of the cell from dilution and harmful solutions that could cross the membrane and disrupt normal cell activity or mitosis.
Like many natural forces, osmosis is a force that pushes solutions towards a state of equilibrium. When a solution surrounded by a thin membrane contains a higher concentration of a chemical, such as salt or sugar, than the same solution outside the membrane, equilibrium forces drive the entire solution towards a state of uniform concentration of chemicals . This natural process is especially important with respect to water in life forms on Earth, which has a potential energy level that causes it to dilute concentrated solutions through various forces such as osmosis and gravity. This condition is referred to as water potential, and the ability of water to exert this force increases with the volume and depth of the water, which is a form of osmotic hydrostatic pressure.
While the water potential is an equalizing force for several solutions, the opposite of this force is known as the osmotic potential, which is the potential energy value that the osmotic pressure must resist in an equilibrium state. Calculations to determine the true value of osmotic pressure were first worked out by Jacobus Hoff, a Nobel Prize-winning Dutch chemist in the late 19th and early 20th centuries. His ideas were later refined by Harmon Morse, an American chemist of the same period.
Since the osmotic pressure process can also be considered for gases separated by a semipermeable membrane, it obeys the same physical rules as the ideal gas law. The osmotic pressure equation can then be stated as P = nRT/V, where “P” is the osmotic pressure and “n” is the amount of solute or the number of moles of molecules present in the volume – “V” – of solution. The value of “T” represents the average temperature of the solution and “R” is the value of the gas constant of 8,314 joules per degree Kelvin.
While osmotic pressure is important in cell biology for animals in terms of protecting the cell from the intrusion of unwanted chemical solutes or the external solution itself, in plants it serves a more fundamental purpose. By counteracting the strength of water potential, plant cells use osmotic pressure to impart a certain degree of turgidity or stiffness to plant cell walls. By combining this force between multiple plant cells, it gives the plant the ability to produce stems that stand upright and can resist the damage of climatic forces such as wind and rain. This is why plants tend to wither and wilt when they lack water, as cell walls have insufficient osmotic hydrostatic pressure to resist the forces of gravity and atmospheric conditions.
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