1. What is Water Potential?

2. Water potential
____________________________________________________________________
Has the symbol psi
Is measured in bars or megapascals
                                  

3. It is a measure of the free energy of water which is less when it is has to surround solutes.
We are really stuck here, YUK!
Well I told you not to come here!
But, I HAVE to join the party!

4. Has two components:
______________(also called osmotic potential) џs which is determined by solute concentration
Pressure potential џp which results from exertion of pressure on membranes/walls as water moves in or out; ______________________

5. The water potential of pure water is given the _____________
Because pure water has the highest concentration of water molecules, and thus the highest water potential, the water potential of all other solutions must be lower than zero i.e. negative.

6. Pure water: = _____

7. Adding solute decreases water potential!
The more solute there is present in a solution _______________________________________
So, solute potential will be a negative number if not pure water.
So hypertonic solutions have negative solute potentials.

8. ________________________________________________________
(s is pi on your paper)

9. Water moves from areas of higher water potential to areas of lower water potential (i.e. towards the more negative, concentrated region).  
____________________________________________________

10. This will occur until the water potential inside the cell equals the water potential outside of the cell.

11. If this makes no sense whatsoever the key information to learn is:
The equation given
the water potential of pure water is zero
water moves from areas of higher water potential to areas of lower water potential (i.e. towards the more negative region)

12. If a cell’s ΨP = 5 bars and its ΨS = -7 bars, what is the resulting Ψ
If a cell’s ΨP = 5 bars and its ΨS = -7 bars, what is the resulting Ψ? If this cell is placed in pure water, which way will water move?

13. Units will cancel out to equal bars.
How do you go from molarity of a solution to the solute potential to figure the wp?
Another equation
solute potential = -iCRT
I = ___________________________
C = molar concentration of sucrose (in this case where no net gain/loss of water occurs)
R = pressure constant ( liter/bars/mole 0K for sucrose)
T = ___________________________
Units will cancel out to equal bars.

14. So what is the solute potential of a 0.1 M solution of sucrose at 22 C?
Solute potential = -iCRT
i (ionization constant) = 1
R = (from handbook)
T = temp K (273 + C of solution)
Ωs = _________________________
Ωs = bars

15. So, how do you get the water potential?
Once you determine the solute potential, plug into the equation to determine the water potential. The pressure potential will be zero since water is at equilibrium (no net movement in or out.

16. NaCl dissociates into 2 particles in water: Na+ and Cl-
NaCl dissociates into 2 particles in water: Na+ and Cl-. If the solution contained 0.1M NaCl, what is the Ψ of the solution if the pressure potential is 2 bars? Temp is 20 degrees Celsius