1. Diffusion Osmosis Lab

2. Osmosis
Osmosis = the movement of water molecules from a region of higher water potential to a region of lower water potential through a partially permeable membrane. Osmosis is considered in terms of water potential and solute potential.

3. Water Potential
Water potential = a measure of the kinetic energy of water molecules. Here, water molecules are constantly moving in a random fashion. Some of them collide with cell membrane, cell wall, creating a pressure on its known as water potential.
The higher their kinetic energy the more they move and hit the membrane, therefore higher the water potential

4. Water potential
How does water move?
Why does water move? 1.
Downhill
Pressure potential 2.
Hose, straw 3.
Fresh – salty
Osmotic/solute potential 4.
Sponge
Matric potential

5. Components of Water Potential
Pressure potential: pushing (positive pressure, like the hose)
sucking (negative pressure, like a straw) Major factor moving water through plants
Osmotic, or Solute potential: reduction in water potential due
to the presence of dissolved solutes
Dissolved substances dilute pure water, so
salty water has lower water potential (lower concentration) than pure water

6. Water Potential Unit of measurement: megapascals (Mpa)
1 MegaPascal = 10 atm = psi
Water potential for pure water: 0
Anything that lowers the “free energy”of water lowers it potential.
-dissolved solutes

7. Water potential = pressure potential + solute potential

8. Clarifying Water Potential Values
(2) Factors to consider:
p = pressure potential (outside & inside)
s = solute potential
system = p + s
SO……
 p results in “+” value
 p results in “-” value

9. Water Potential Values
High water potential (+Value):
- less solute
- more water
- (hypotonic)
Zero (0) Value:
- Pure water
Low water potential (-Value):
- More solute
- less water
- (hypertonic)
****Water will move across a membrane in the direction of the lower water potential****

10. Analysis of the Data Collected
Mass Difference: Final – initial (absolute diff.)
% Change in Mass: Final – initial x 100
initial
**Why do we use the % change in mass instead of simply the straight difference?
Plot your data on the graph.
Determine the molar solute concentration of the potato cores. How???
***Where your line crosses the “0” mark

11. Calculating Solute Potential
Variables involved: i, C, R, T
i = ionization constant: NaCl = 2.0 (Na+ & Cl-)
**for sucrose it will be 1.0 (it doesn’t ionize)
C = Molar concentration of your potato (graph)
R= rate constant: L · atm (bar)
mol · K
T = Temperature: K

12. Calculating the Solute Potential (s)
s = - iCRT
Sample Calc.
A 1.0 M sugar 22° C under standard atmospheric conditions:
s = -(1)(1.0mol)( L · bar )(295K)
L mol · K
s = bars

13. Typical Water Potential Values
Outside air (50% humidity): MPa
Outside air (90% humidity): MPa
Leaf Tissue: MPa
Stem: MPa
Root: MPa
Soil water: MPa
Hydrated soil (Saturated) MPa
** When the soil is extremely dry what happens to the water potential and water movement into the plant?
**Does the value become more negative or more positive?

14. Water Potential in Plants

15. Water Balance (pg. 117-118) Osmoregulation~ control of water balance
Hypertonic~ higher concentration of solutes
Hypotonic~ lower concentration of solutes
Isotonic~ equal concentrations of solutes
Cells with Walls:
Turgid (very firm)
Flaccid (limp)
Plasmolysis~ plasma membrane pulls away from cell wall

16. Dialysis Tubing Experiment

17. An Artificial Cell Permeable to: monosaccharides & water Impermeable to: Disaccharides

18. Introductory Questions #3 (Lab)
Suppose you have an artificial cell that was permeable to monosaccharides and impermeable to disaccharides. What would happen to the cell if it had 0.80 M maltose and 0.85 M fructose in it and was placed in a solution containing 0.45 M glucose, 0.65 M fructose, and 0.40 M sucrose.
a) Which direction would the water flow?
b) Which area has a higher water potential?
c) What would happen to the concentration of the maltose inside the cell (increase, decrease, remain the same)?
What is the ionization constant (i) for sucrose?
Determine the “C” value for your potato cores. (guidesheets)
Graph your results:
% change in mass vs. sucrose molarity within the beakers
(guidesheets)

19. Key Sections you need for your Lab
Title
Intro/Background: Defining water potential
Importance & Sig. Of the lab
Hypothesis & reason for your prediction
ID Experimental Variables
Materials (diagram & visual of set up optional)
Procedure
Data: tables charts & graphs
Analysis- be thorough
Conclusion & Evaluation: error & improvements

20. Introductory Questions # (lab)
Explain how potential energy is different from kinetic energy. What are some ways we can measure energy?
2) Define each variable in the equation:
∆G = ∆H – T ∆S
3) What is the difference between an exergonic reaction and an endergonic reaction?
How is ATP associated with coupled reactions? What purpose does it serve?
How is an electron carried from one molecule to the next? Name a molecule that can carry an electron.
6) How is Anabolism different from catabolism?
7) Briefly explain how the first two laws of thermodynamics apply to a living organism

21. Lab #3: Water Potential & Osmosis
Read the Handout provided
Go to my web site and click on:
“Review of 12 AP Labs”
Click on the hyperlink shown on the worksheet
Choose Lab #1: Diffusion & Osmosis
Go through the tutorial and READ each section.

22. What to have Ready for Tomorrow
Bring in a Large Potato (one per lab table)
Have the Pre-lab finished w/quiz
Write a statement of purpose or reason for doing this lab
Materials list - review the handout
Hypothesis:
Data Table – review website or others for an idea.
**Need (2): Individual data & class Data

23. Introductory Questions #3 (Lab)
Suppose you have an artificial cell that was permeable to monosaccharides and impermeable to disaccharides. What would happen to the cell if it had 0.80 M maltose and 0.85 M fructose in it and was placed in a solution containing 0.45 M glucose, 0.65 M fructose, and 0.40 M sucrose.
a) Which direction would the water flow?
b) Which area has a higher water potential?
c) What would happen to the concentration of the maltose inside the cell (increase, decrease, remain the same)?
What is the ionization constant (i) for sucrose?
Determine the “C” value for your potato cores. (guidesheets)
Graph your results:
% change in mass vs. sucrose molarity within the beakers
(guidesheets)

24. Questions to answer from the Website- Prelab
How many concepts are there?
How many Exercises are there for
designing the experiment?
After looking at the Analysis & Results portion of tutorial define each of following terms: i = C= R = T=
Do the 5 question quiz and print out your results.

25. Answers for the Website- Prelab
How many concepts are there?
How many Exercises are there for
designing the experiment? 5
After looking at the Analysis & Results portion of tutorial define each of following terms:
i = ionization constant
C= molar concentration of the potato
R= rate constant: L · atm (bar)
mol · K
T= temperature (K) C
Do the 5 question quiz and print out your results.
1. C 2. D 3. E 4. B 5. A