Osmosis Flashcards
What is the definition of osmosis?
The passage of water from a region of higher water potential to a region where it has lower water potential through a selectively permeable membrane.
What does it mean for cell membranes and plasma membranes to be selectively permeable?
They are permeable to water molecules and a few other smaller molecules, but not to larger molecules.
What is a solute?
A solute is any substance that is dissolved in a solvent, e.g. water. The solute and the solvent together form a solution.
What is water potential?
Water potential is the pressure created by water molecules. Pure water has a water potential of zero.
Key points of water potential:
- Adding solute to water lowers water potential.
- Water potential of a solution must always be less than 0, a negative value.
- The more concentrated a solution, the lower or more negative its water potential.
- Water will move by osmosis from a less negative (higher) water potential, to a more negative (lower) water potential.
How can you find the water potential of cells or tissues?
Place them in a series of solutions of different water potentials. Where there is no net gain or net loss of water from cells or tissues, the water potential must be the same as the external solution.
What is the feature of animal cells which prevents cells from bursting, and releasing its contents?
The cells live in a liquid which has the same water potential as its cells. For example, red blood cells live in blood plasma. If a cell is placed in a solution lower than its own water potential, water leaves by osmosis, causing the cell to shrivel.
What happens to the cell when the water potential of external solution is higher (less negative)?
Net movement of water is into the cell, causing cell to swell and burst. This is known as the cell being turgid.
What happens to the cell when the water potential of external solution is equal?
No net movement of water, the state of cell doesn’t change. The condition of the cell is known as incipient plasmolysis.
What happens to the cell when the water potential of external solution is lower (more negative)?
Net movement of water is out of the cell, causing cell to shrink. The condition of the cell is known as plasmolysed.
