Osmosis
Animal cells
In plant cells
Solute potential
Water potential
Pressure potential
Water
Turgor and plasmolyds
Has no cell wall so pressure potential doesn't need to be considered
The water potential is the same as the solute potential
Haemolysis
If red blood cells are I distilled water, water enters by osmosis and burst because have no cell wall.
If red blood cells are placed in concentrated salt solution, water leaves the cells and they shrink, becoming crenated.
If water potential of a solution is less negative (higher) than the solution inside the cell, it is hypotonic and water flows in to the cell.
If water potential of the external solution is more negative (lower) than the solution inside the cell, it is hypertonic and water flos out of the cell.
If the cell has the same water potential as the surrounding solution, the external solution and cell are isotonic and there will be no net water movement.
Water entering a plant by osmosis expands the vacuole and pushes the cytoplasm against the cell wall, which can only expand a little before becoming turgid and no more water is allowed in.
Plant cells are under the influence of opposing forces
Solute potential due t 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 in which increases the tendency of water to move out.
Water potential of cell = pressure potential + solute potential
A measure of free energy of water molecules and is the tendency for water to move.
Pure water has a water potential of zero. The addition of a solute to pure water brings water molecules in.
Where there is a high concentration of water molecules, water molecules have a high potential energy because they are free to move.
In a solution, water molecules are weakly bound to the solute so few are free to move. The system has a lower potential energy.
External water molecules with higher potential energy will move down an energy gradient to the lower potential energy. This is the pulling force they experience, which is the osmotic pull inwards.
A more concentrated solution has even fewer free water molecules which means the pull on water molecules is greater so the water potential is more negative (lower).
Measures how easily water molecules move out of a solution. The more solute present, the more tightly water molecules are held, the lower the tendency of water to move out. So a higher concentration has a lower, more negaive solute potential.