| what does high water potential mean | this means the solution has a high water concentration (so not very much solute dissolved in it) |
| what does low water potential | this means the solution has a low water concentration (so lots of solute dissolved in it) |
| what kPa is pure water | water potenital of 0 kPa , and the value decreases (becomes more negative) as more solute is added |
| osmosis meaning | diffusion of water molecules across a partially permeable membrane from an area of higher water potential to an area of lower water potential. |
| what happens in osmosis | Water molecules diffuse down a water potential gradient until the water potential is equal on both sides of the membrane (equilibrium). |
| hypotonic solutions in animal cells | A hypotonic solution has a higher water potential than the cell.
Water molecules move into the cell.
The cell swells and bursts. |
| isotonic solutions in animal cells | An isotonic solution has the same water potential as the cell.
There is no net movement of water into or out of the cell.
The cell stays the same size. |
| hypertonic solutions in animal cells | A hypertonic solution has a lower water potential than the cell.
Water molecules move out of the cell.
The cell shrinks. |
| hypotnic solutions in plant cell | A hypotonic solution has a higher water potential than the cell.
Water molecules move into the cell.
The cell swells and becomes turgid. |
| isontonic solutions in plant cells | An isotonic solution has the same water potential as the cell.
There is no net movement of water into or out of the cell.
The cell stays the same size. |
| hypertonic solutons in plant cells | A hypertonic solution has a lower water potential than the cell.
Water molecules move out of the cell.
The cell shrinks and becomes plasmolysed. |
| Factors affecting the rate of osmosis | Temperature - At higher temperatures, water molecules have more kinetic energy and diffuse faster.
Water potential gradient - The steeper the gradient, the faster the rate of osmosis.
Thickness of membrane - Water molecules travel shorter distances through thin exchange surfaces, so diffuse faster.
Surface area - Larger surface areas mean more water molecules can cross the membrane at once, making osmosis faster. |
