1. Marking Period 2 Grades Finish grading ecology projects Chapter 6 Quiz
AP Lab 4 PreLab Quiz
Microscope Lab
Cells Quiz/Test on Monday
One of your case studies

2. Solutions and Water Potential
PSI
Solutions and Water Potential
Chapter 7
Agenda:
Ch 6 Quiz
Notes
- Practice
Hw: Pre-Lab

3. Interactive Question 7.5 Side A Side B 1 M Glucose 0.2 M Fructose
5/2/2018
Interactive Question 7.5
A solution of 1 M glucose is separated by a selectively permeable membrane from a solution of 0.2 M fructose and 0.7 M sucrose. The membrane is not permeable to sugars. Indicate which side initially has more free water molecules and which side has fewer. Explain the direction of osmosis.
Side A Side B
Clustering of free water molecules around solute particles lowers the proportion of free water that is available to cross the membrane.
1 M Glucose
0.2 M Fructose
0.7 M Sucrose

4. Interactive Question 7.6
A. What osmotic problems does the freshwater protist Paramecium face, and what adaptations enable it to osmoregulate? B. Compare the ideal osmotic environment for animal cells and plant cells.

5. Cell survival depends on balancing water
uptake & loss = OSMOREGULATION
Paramecium vs. pond water
Paramecium is hypertonic
H2O continually enters cell
to solve problem, specialized organelle, contractile vacuole

6. TONICITY- ability of a solution to cause a cell to lose or gain water
Refers to the concentration of SOLUTES
Is a RELATIVE term, comparing two different solutions
Solute-substance that is dissolved
Solvent- substance solute in dissolved in
Solution = solute + solvent

7. Animation See an animation Osmosis1

8. Osmosis…
.05 M
.03 M
Cell (compared to beaker)  hypertonic or hypotonic
Beaker (compared to cell)  hypertonic or hypotonic
Which way does the water flow?  in or out of cell

9. 5/2/2018
Hypo Iso Hyper
Hyper: Animal cell will crenate, Plasmolysis: Plant cell
Hypotonic: Animal cell with swell Cytolysis
Turgor pressure provides support for nonwoody plants. Plant cells = iso = flaccid. Need hypotonic.

10. Animal

11. I’m a slug baby. Ain’t no shell over here.
Water rush out of the cell to surface.
Decrease
Water
Potential

12. Water moves from High Free Energy (Potential) to Low Potential
Water potential (ψ): H2O moves from high ψ  low ψ potential
Water potential equation:
ψ = ψs + ψp
Water potential (ψ) = free energy of water
Solute potential (ψS) = solute concentration (also called osmotic potential)
Pressure potential (ψP) = physical pressure on solution; turgor pressure (plants)
Pure water: ψP = 0 MPa
Plant cells: ψP = 1 Mpa

13. Bars or Megapascals
Water potential is measured in bars or megapascals (MPa)
1 MPa = 10 bars
Water potential is the tendency of water to leave one place in favor of another.
The water pressure of pure water in an open container is zero ψ = 0

14. Slug Example Pure Water = 0 Bars
Outside of cell
High concentration or potential to LOW
Inside of cell

15. Where will WATER move? From an area of:
higher ψ  lower ψ (more negative ψ)
high pressure  low pressure
Solution concentration low -->> high

16. Diffusion
Water
Trees
Pure water = 0

17. ψ = ψs + ψp Two plant cells Solute Potential Osmotic Pressure
Adding solutes is going to LOWER the solute potential.
Less room for water.

18. ψ = ψs + ψp Two plant cells Solute Potential Osmotic Pressure
= -5 bars = 2 bars
Adding solutes is going to move water into the other cell.
Osmotic pressure will increase. Turgid.

19. Calculating Solute Potential (ψS)
5/2/2018
ψ = ψs + ψp
Calculating Solute Potential (ψS)
ψS = -iCRT
i = ionization constant (# particles made in water)
NaCL = 2
Sucrose = 1
C = molar concentration (moles/liter or M)
R = pressure constant ( liter bars/mole-K)
T = temperature in K ( C)
The addition of solute to water lowers the solute potential (more negative) and therefore decreases the water potential.
NaCl is 2 because if you add 1 mole of NaCl it breaks apart into 1 mole of Na and 1 mole of Cl..
Increasing i is going to lower the solute potential (s), Increase concentration also lower solute potential (s)
Increase temperature lower water potential

20. Which chamber has a lower water potential?
Which chamber has a lower solute potential?
In which direction will osmosis occur?

21. Sample Problem Mr. Anderson

22. Sample Problem
Calculate the solute potential of a 0.1M NaCl solution at 25°C.
If the concentration of NaCl inside the plant cell is 0.15M, which way will the water diffuse if the cell is placed in the 0.1M NaCl solution?