osmosis

• Osmosis


  Net movement of water molecules from region of higher water potential to a region of lower water potential through a partially permeable membrane
• Osmosis


  1. Water molecules collide with the membrane, applying pressure to the membrane

  2. Both sides will have same water potential, reached equilibrium so osmosis stops

  3. Water molecules still move across membrane but same number in each direction (net movement is zero)
• Water potential


  Measure of the tendency of water to move from one area to another by osmosis (in kilopascals)
• Pure water has highest possible water potential as it has highest possible concentration of water molecules (0kPa)
• Water potential of any solution must be less than zero (negative number)
• More concentrated solution has lower water potential - less water molecules
• Isotonic


  Water potential in solution same as cell
• Hypotonic


  Water potential of solution more positive (closer to zero)
• Hypertonic


  Water potential of solution more negative than cell
• Placed in hypotonic solution (pure water)


  1. Water will move into cells by osmosis

  2. Animal cells don’t have cell walls - pressure causes cell to burst

  3. Plant cells have a cell wall - pressure causes cell to become turgid
• Placed in hypertonic solution


  Both animal and plant cells will become shrivelled - water leaves cell by osmosis