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Water Potential
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I. Water Potential (ψ) A. free energy per mole of water
B. predicts which way water diffuses C. based on 2 factors 1. solute potential – potential energy created by solute concentrations 2. pressure potential- potential energy created by pressure
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II. Free energy of Water & water concentrations
A. Based on free water B. Water that is H-bonded to solutes is not free C. More free water = more free energy = higher ψ D. Water moves from high free water areas to low free water areas Solute free water Solute water potential
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Iii. Solute potential A. potential energy generated by water’s tendency to move toward hypertonic areas B. solute potential of distilled water is 0 C. solute potential is based on – i D. solute potential of any solution is negative E. since water moves from high ψ to low ψ…. water flows toward the more negative solution
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Iv. Pressure Potential A. negative pressure = tension
1. water evaporates from leaves creates negative pressure that pulls more water up from roots. B. positive pressure = turgor pressure/osmotic pressure
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C. Plant Cells
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D.Animal Cells A. crenation - caused by water leaving creates tension
B. Normal cell in isotonic solution = equal water potential C. Osmotic pressure – created as cell swells D. Lysis – cell membrane breaks
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Prediction : water moves from high ψ to low ψ
High water potential Low water potential
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II. Formula Water potential = pressure potential + solute potential
ψ = ψ p + ψ s Pressure potential in an open container is 0 Pressure potential in an animal cell is 0 ….why? no cell wall so no turgor pressure
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III. Calculating solute potential
Ψs = - i C R T i = ionization constant = # particles a molecule makes when dissolved in H2O C = molar concentration R = pressure constant = T = temperature K (273 + ◦C)
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