The osmotic pressure is the pressure required to achieve osmotic equilibrium. We can see from this equation that the amount of solute present in the solution will directly affect the osmotic pressure of the system.
Boundless vets and curates high-quality, openly licensed content from around the Internet. This particular resource used the following sources:. Skip to main content. Search for:. Osmotic Pressure. Since there is a flow of solvents, the height of each side changes, which is osmotic pressure.
When we work with aqueous solutions, we use mm of H 2 O to describe the difference. Osmosis is the diffusion of a fluid through a semipermeable membrane. When a semipermeable membrane animal bladders, skins of fruits and vegetables separates a solution from a solvent, then only solvent molecules are able to pass through the membrane. In biological systems, water is the solvent and plasma membranes are the semipermeable membranes.
Plasma membranes allow water molecules to pass, due to protein channels, known as aquaporins, as well as small non-polar molecules that diffuse rapidly across them, whereas they are impermeable to ions and macromolecules. Inside the cell there are macromolecules, such as nucleic acids, proteins , glycogen, and supramolecular aggregates, for example multienzyme complexes , but also ions in a higher concentration than that of the extracellular environment.
This causes osmotic pressure to drive water from outside to inside the cell. If this net flow of water toward the inside of the cell is not counterbalanced, cell swells, and plasma membrane is distended until the cell bursts, that is, an osmotic lysis occurs. Under physiological conditions, this does not happen because during evolution several mechanisms have been developed to oppose, and in some cases even exploit, these osmotic forces.
Two of these are energy-dependent ion pumps and, in plants, bacteria and fungi, the cell wall. Ion pumps reduce, at the expense of ATP, the intracellular concentrations of specific ions with respect to their concentrations in the extracellular environment, thereby creating an unequal distribution of the ions across the plasma membrane, namely, an ion gradient. In this way the cell counterbalances the osmotic forces due to the ions and macromolecules trapped inside it.
Plant cells are surrounded by an extracellular matrix, the cell wall , that, being non expandable and positioned next to the plasma membrane, allows cell to resist osmotic forces that would cause its swelling and finally the lysis. Large quantities of solutes, for the most part organic and inorganic acids, are accumulated within them and osmotically draw water, causing their swelling.
In turn, this causes the tonoplast , the membrane that surrounds the vacuole, to press the plasma membrane against the cell wall, that mechanically opposes to these forces and avoids the osmotic lysis.
This osmotic pressure is called turgor pressure , and can reach up 2 MPa, that is, 20 atmospheres, a value about 10 times higher than the air pressure in tires. It is responsible for the rigidity of non woody parts of plants, is involved in plant growth, as well as in:.
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