Water Potential( Ψ)
Commonly reprisented by the greek letter Ψ Biologists use this term to describe the tendency of water to leave one place in favor of another. Water always moves from an area of higher water potential to an area of lower water potential.
Water potential is affected by 2 factors:
-Pressure
- Amount of solute
When a blood cell is dropped in distilled water, it will pop like a balloon. Water will move into the cell and cause it to expand.
However,
If a plant cell is placed in distilled water, water will enter the cell, but will not pop because of the elastic cell wall, which will exert back pressure which will limit the gain of water.
Water potential formula: Water Potential = Pressure potential + Solute potential
Pressure potential : (in a plant cell) Pressure exerted by the rigid cell wall that limits further water uptake .Hydrostatic pressure that is exerted on water in a cell.
Solute potential : The component of water potential that is due to the presence of solute molecules. It always has a negative value as solutes lower the water potential of the system.
The water potential of pure water in an open container is zero because there is no solute and the pressure in the container is zero. Adding solute lowers the water potential. When a solution is enclosed by a rigid cell wall, the movement of water into the cell will exert pressure on the cell wall. This increase in pressure within the cell will raise the water potential.
Solutions:
Hypotonic: A hypotonic solution has a lower solute concentration and a higher water potential than the solution on the other side of the membrane; water will move down its concentration gradient into the other solution.
Hypertonic: A hypertonic solution has a higher solute concentration and a lower water potential as compared to the other solution; therefore, water will move into the hypertonic solution through the membrane.
Isotonic: Isotonic solutions have equal water potential.
Water potential is affected by 2 factors:
-Pressure
- Amount of solute
When a blood cell is dropped in distilled water, it will pop like a balloon. Water will move into the cell and cause it to expand.
However,
If a plant cell is placed in distilled water, water will enter the cell, but will not pop because of the elastic cell wall, which will exert back pressure which will limit the gain of water.
Water potential formula: Water Potential = Pressure potential + Solute potential
Pressure potential : (in a plant cell) Pressure exerted by the rigid cell wall that limits further water uptake .Hydrostatic pressure that is exerted on water in a cell.
Solute potential : The component of water potential that is due to the presence of solute molecules. It always has a negative value as solutes lower the water potential of the system.
The water potential of pure water in an open container is zero because there is no solute and the pressure in the container is zero. Adding solute lowers the water potential. When a solution is enclosed by a rigid cell wall, the movement of water into the cell will exert pressure on the cell wall. This increase in pressure within the cell will raise the water potential.
Solutions:
Hypotonic: A hypotonic solution has a lower solute concentration and a higher water potential than the solution on the other side of the membrane; water will move down its concentration gradient into the other solution.
Hypertonic: A hypertonic solution has a higher solute concentration and a lower water potential as compared to the other solution; therefore, water will move into the hypertonic solution through the membrane.
Isotonic: Isotonic solutions have equal water potential.