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The osmotic entry of water raises the turgor pressure exerted against the cell wall, until it equals the osmotic pressure, creating a steady state.When a plant cell is placed in a solution that is hypertonic relative to the cytoplasm, water moves out of the cell and the cell shrinks. In extreme cases, the cell becomes plasmolyzed – the cell membrane disengages with the cell wall due to lack of water pressure on it.For example, if the cell is submerged in saltwater, water molecules move out of the cell.
Permeability depends on solubility, charge, or chemistry, as well as solute size.
Water molecules travel through the plasma membrane, tonoplast membrane (vacuole) or protoplast by diffusing across the phospholipid bilayer via aquaporins (small transmembrane proteins similar to those responsible for facilitated diffusion and ion channels).
When the membrane has a volume of pure water on both sides, water molecules pass in and out in each direction at exactly the same rate.
There is no net flow of water through the membrane.
is the spontaneous net movement of solvent molecules through a selectively permeable membrane into a region of higher solute concentration, in the direction that tends to equalize the solute concentrations on the two sides.
It may also be used to describe a physical process in which any solvent moves across a selectively permeable membrane (permeable to the solvent, but not the solute) separating two solutions of different concentrations.Osmotic pressure is defined as the external pressure required to be applied so that there is no net movement of solvent across the membrane.Osmotic pressure is a colligative property, meaning that the osmotic pressure depends on the molar concentration of the solute but not on its identity.One fact to take note of is that heat from the surroundings is able to be converted into mechanical energy (water rising).Many thermodynamic explanations go into the concept of chemical potential and how the function of the water on the solution side differs from that of pure water due to the higher pressure and the presence of the solute counteracting such that the chemical potential remains unchanged.The virial theorem demonstrates that attraction between the molecules (water and solute) reduces the pressure, and thus the pressure exerted by water molecules on each other in solution is less than in pure water, allowing pure water to "force" the solution until the pressure reaches equilibrium.Osmotic pressure is the main cause of support in many plants.The more concentrated the salt solution, the bigger the difference in size and weight of the potato slice.In unusual environments, osmosis can be very harmful to organisms.Plants concentrate solutes in their root cells by active transport, and water enters the roots by osmosis.Osmosis is also responsible for controlling the movement of guard cells.