osmosis

• What is osmosis?


  The passage of water from a region where it has a less negative water potential to a region where it has a more negative water potential through a selectively permeable membrane.
• What is a solute?

  Any substance that is dissolved in a solvent e.g. water this forms solution.
• What is water potential measured in?


  Units of pressure usually kilopascals.
• What is water potential?


  Water potential is the pressure created by water molecules.
• What is the water potential of water?


  0, the additional addition of a solute will ,lower the water potential.
• How do 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 loss of water from the cells, the water potential inside the cells must be the same as the external solution.
• Explain why happens osmosis.

  A solution on the left has a low concentration of solute molecules while the solution on the right has a high concentration of solute molecules.

  Both solutions are in random motion due to kinetic energy.

  The plasma membrane only allows water across it and not solute molecules.

  The water then diffuses from the left side with higher water pot to right with lower pot down the concentration gradient.
• Why do animal cells live in a liquid with the same water potential?


  Animal cells such as red blood cells contain a variety of solutes dissolved in them.

  If a rbc is placed in pure water it will absorb water by osmosis as it has a more negative water potential.

  As plasma membranes are thin and flexible they will end up bursting open the cell- in rbc its called haemolysis.

  If a rbc water potential is more negative, water will leave the cell by osmosis and the cell will become shrivelled.