Water Potential

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Water Potential

  1. 1. Concept of Water Potential (  , psi)
  2. 2. Water Potential <ul><li>Physical property of water that determines the direction that water will flow. </li></ul><ul><li>In the world of water potential 0 is high! </li></ul><ul><ul><li>Usually a negative number </li></ul></ul><ul><ul><li>Occasionally a positive number </li></ul></ul><ul><li>Determined by the solute concentration and pressure </li></ul>
  3. 3. Water Potential <ul><li>Water potential = Osmotic Potential + Pressure Potential </li></ul><ul><li> s  p </li></ul><ul><li>Measured in bars </li></ul><ul><ul><li>a metric measure of pressure </li></ul></ul>
  4. 4.  =  s +  p <ul><li> s = the solute (or osmotic) potential </li></ul><ul><li> s = – iCRT </li></ul><ul><ul><li>i = ionization constant (number of particles formed) </li></ul></ul><ul><ul><ul><li>Glucose (1) </li></ul></ul></ul><ul><ul><ul><li>NaCl (2) </li></ul></ul></ul><ul><ul><ul><li>CaCl 2 (3) </li></ul></ul></ul>
  5. 5.  =  s +  p <ul><li> s = the solute (or osmotic) potential </li></ul><ul><li> s = – iCRT </li></ul><ul><ul><li>i = ionization constant (number of particles formed) </li></ul></ul><ul><ul><li>C = osmotic molar concentration of the solute </li></ul></ul><ul><ul><li>R = pressure constant (handbook value R=0.0831 liter bars/mole o K) </li></ul></ul><ul><ul><li>T = temperature in o K (273 + o C) of solution </li></ul></ul>
  6. 6. Water Potential <ul><li> =  s +  p </li></ul><ul><ul><li> s = the solute (or osmotic) potential </li></ul></ul><ul><ul><li> s = – iCRT </li></ul></ul><ul><ul><li> p = the pressure potential </li></ul></ul><ul><ul><ul><li>A solution open to the atmosphere has a pressure potential of 0 bars </li></ul></ul></ul>
  7. 7. Water Potential Principles <ul><li>Water always moves from high water potential to low water potential </li></ul><ul><li>Water potential is a tendency of water to move from high free energy to lower free energy </li></ul><ul><li>Distilled water in an open beaker has a water potential of 0 (zero) </li></ul>
  8. 8. Water Potential Principles <ul><li>Addition of solute decreases water potential </li></ul><ul><li>Addition of pressure increases water potential </li></ul><ul><li>In cells, water moves by osmosis to areas where water potential is lower. </li></ul><ul><ul><li>A hypertonic solution has lower water potential </li></ul></ul><ul><ul><li>A hypotonic solution has higher water potential </li></ul></ul>

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