osmosis

• Osmosis


  The diffusion of water molecules from a region of higher water potential to a region of lower water potential through a partially or selectively permeable membrane
• Osmosis is a passive process that does not require metabolic energy
• Partially permeable membrane


  • Water molecules can pass freely across
  • Solute molecules cannot pass across
• Higher concentration of water molecules on one side of the membrane

  Higher water potential on that side
• Water molecules diffuse from higher water potential to lower water potential


  This is osmosis
• At equilibrium, the water potential is the same on both sides and osmosis stops
• Water potential


  Pressure exerted by water molecules, measured in kilopascals
• Pure water has the highest possible water potential, set at 0 kilopascals
• More concentrated solution


  Lower water potential (negative number)
• Glucose solutions


  • Solution with lower water potential (-100 kPa)
  • Solution with higher water potential
• Older terms like hypertonic, hypotonic and isotonic are no longer used, osmosis is now described in terms of water potential