1. Water Potential

2. 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

3. 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

4. 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

5. 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

6. C. Plant Cells

7. 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

8. Prediction : water moves from high ψ to low ψ
High water potential
Low water potential

9. 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

10. 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)