61 WJEC Biology AS Level - Marianne Izen - 2nd Edition (1.3 Cell Membranes And Transport) Flashcards
What is the extra factor concerning water movement in a plant cell?
In a plant cell, the presence of the cell wall introduces an extra factor concerning water movement into and out of cells.
What is the pressure potential?
Water entering a plant cell by osmosis expands the vacuole and pushes the cytoplasm against the cell wall.
The cell wall can only expand a little and so pressure outwards builds up, resisting the entry of more water, making the cell turgid.
This pressure is the pressure potential, and as it is a push outwards it has a positive sign.
What are the forces that influence a plant cell?
Plant cells are under the influence of two opposing forces:
- The solute potential, which is due to the solutes in the vacuole and cytoplasm pulling water in. The higher these concentrations, the less likely the water is to move out.
- The pressure potential, a force which increases the tendency of water to move out.
The balance of these two forces determines the water potential of the cell and whether water moves in or out.
What is the equation for water potential of a cell?
Calculate the water potential and the pressure potential
Draw a diagram to show solute potential and pressure potential.
Turgid (Key-Term)
A plant cell that holds as much water as possible.
Further entry of water is prevented as the cell wall cannot expand further.
What can be the values for:
water potential
solute potential
pressure potential
The water and solute potential are either 0 (for pure water) or negative.
The pressure potential is either 0 (in a cell at incipient or full plasmolysis see below) or positive.
Pressure potential (Key-Term)
The hydrostatic pressure exerted by the cell contents on the cell wall.
It is equal and opposite to the pressure exterted by the cell wall on the cell contents.
