1. Water Potential

3. Water potential Tendency of a solution to take up water
Tendency of water to diffuse from one area to another
 (psi)

4. Water potential Two components to water potential 1. Pressure
Physical forces, can be positive or negative
If positive increased pressure.
If negative decreased pressure.
2. Solute concentration (or osmotic potential)
Always negative

5. Water potential Water potential of a solution is the sum
Solute potential s (osmotic potential)
Pressure potential p
Water potential is expressed as:
= s + p

6. Water potential Pure water =0 Adding solute lowers potential
Less free water molecules
Water moves from a higher water potential to a lower water potential
Less concentrated (hypotonic) to a more concentrated (hypertonic)

7. Animal cells Water movement depends only on solute concentrations.
Hypertonic solution the water moves out and the cell shrinks
Hypotonic solution the water moves in and the cell swells
Bursting (Lysis) can happen.

8. Animal cell

9. Plant cells Cell wall can exert pressure and prevents lysis.
When the pressure inside the cell becomes large enough
No additional water can enter the cell
Even if the cell still has a higher solute concentration.

10. Plant cells Flaccid: Limp-lost water Turgid: Firm-gained water
Plasmolysis:
Plant cell shrinks from cell wall
Lost water

11. Plant cell

12. Lab
                                               
             
                                                                          

13. Environment: 0.01 M sucrose “Cell” 0.01 M glucose 0.01 M fructose
Fig. 7-UN3
Environment:
0.01 M sucrose
0.01 M glucose
0.01 M fructose
“Cell”
0.03 M sucrose
0.02 M glucose

14. (a) 0.1 M solution Pure water H2O ψP = 0 ψS = 0 ψP = 0 ψS = −0.23
Fig. 36-8a
(a)
0.1 M solution
Pure water
Figure 36.8a Water potential and water movement: an artificial model
H2O
ψP = 0 ψS = 0
ψP = 0 ψS = −0.23
ψ = 0 MPa
ψ = −0.23 MPa

15. (b) Positive pressure H2O ψP = 0 ψS = 0 ψP = 0.23 ψS = −0.23 ψ = 0 MPa
Fig. 36-8b
(b)
Positive pressure
Figure 36.8b Water potential and water movement: an artificial model
H2O
ψP = 0 ψS = 0
ψP = ψS = −0.23
ψ = 0 MPa
ψ = 0 MPa

16. (c) H2O ψP = 0 ψS = 0 ψP = ψS = −0.23 ψ = 0 MPa ψ = 0.07 MPa
Fig. 36-8c
(c)
Increased positive pressure
Figure 36.8c Water potential and water movement: an artificial model
H2O
ψP = 0 ψS = 0
ψP =   ψS = −0.23
0.30
ψ = 0 MPa
ψ = MPa

17. (a) Initial conditions: cellular ψ > environmental ψ
Fig. 36-9a
Initial flaccid cell:
ψP = 0 ψS = −0.7
0.4 M sucrose solution:
ψ = −0.7 MPa
ψP = ψS = −0.9
ψ = −0.9 MPa
Plasmolyzed cell
ψP = ψS = −0.9
Figure 36.9 Water relations in plant cells
ψ = −0.9 MPa
(a) Initial conditions: cellular ψ > environmental ψ

18. (b) Initial conditions: cellular ψ < environmental ψ
Fig. 36-9b
Initial flaccid cell:
ψP = 0 ψS = −0.7
ψ = −0.7 MPa
Pure water:
ψP = 0 ψS = 0
ψ = 0 MPa
Turgid cell
ψP = ψS = −0.7
Figure 36.9 Water relations in plant cells
ψ = 0 MPa
(b) Initial conditions: cellular ψ < environmental ψ

20. Ψs = -iCRT
i = ionization constant (for sucrose this is 1.0 because sucrose does not ionize water)
C = Molar concentration (from experiment)
R = Pressure constant (R= liter bars/mole K)
T = temperature in K (273 + C)