AP Biology Diffusion and Osmosis Lab: 4 Name _____________________ Date__________
Lab has been revised from multiple sources received at AP conferences and online resources.
Modified lab from Parul Matani:
Prelab questions
Pre-laboratory Questions
1. Define Diffusion
2. What happens in equilibrium?
3. Define Osmosis
4. What is water potential?
5. What does water potential measure?
6. What are two components that influence water potential?
7. Define Dialysis and explain what determines if a substance can pass through the membrane
8. Explain what it means when two solutions are isotonic and discuss the net direction of the water
flow.
9. Discuss the difference between hypertonic and hypotonic solutions and discuss the next direction
of the water flow.
10. What would happen if you applied saltwater to the roots of a plant? Why?
11. Will water move into or out of a plant cell if the cell has a higher water potential than its
surrounding environment?
12. 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 into the 0.1M
NaCl solution?
13. What must turgor pressure equal if there is no net diffusion between the solution and the cell?
14. A dialysis bag contains a sucrose solution of 0.6 M. The beaker into which it is placed has a
concentration of 0.3M. Is the dialysis tubing hypertonic or hypotonic to the beaker solution? In
which direction is the water expected to go?
AP Biology Diffusion and Osmosis Lab: 4 Name _____________________ Date__________
15. What solution would the beaker need to contain in order for there to be no net movement of
water between the 0.6M bag and the beaker?
16. If a potato core is placed in water, which do you expect will be the direction of water flow?
17. Discuss the difference between animal and plant cell responses when placed in hypotonic
solutions.
18. Does increasing pressure increase or decrease water potential?
19. Does increasing solute concentration increase or decrease water potential?
20. Will water go from area of -3 water potential to one of 0 water potential or vise versa? Explain
AP Biology Diffusion and Osmosis Lab: 4 Name _____________________ Date__________
Names of group members:________________________________________________________
What causes my plants to wilt if I forget to water them?
Here is an essay question from a previously released College Board AP Biology Exam:
A laboratory assistant prepared solutions of 0.8 M, 0.6 M, 0.4 M, and
0.2 M sucrose, but forgot to label them. After realizing the error, the assistant randomly labeled
the flasks containing these four unknown solutions as flask A, flask B, flask C, and flask D.
Design an experiment, based on the principles of diffusion and osmosis, that the assistant
could use to determine which of the flasks contains each of the four unknown solutions.
Procedure 1: Effect of Osmosis on a Plant Cell
Materials
• Distilled or tap water
• 1 M sucrose
• 1 M NaCl
• 1 M glucose
• microscope slides and cover slips
Step 1: Start by looking at Elodea under the light microscope. Draw a sketch of a cell at 100X or 400X
magnification in your lab notebook.
Step 2: Treat each cell with one of the following solutions: 1M sucrose, 1MNaCl, 1M glucose, Distilled
water. Each group will have a different solution.
Answer the following questions by labeling your sketch or making observations in your lab notebook.
 Where is the cell membrane in relation to the cell wall? Can you see the two structures easily?
Why or why not?

What parts of the cell that you might see controls the water concentration inside the cell?
Solutions
provided
Predict an outcome
Observed
Results
Turgor pressure
increased or
decreased?
1M sucrose
1M NaCl
1M glucose
Distilled water




What changes do you expect to see when the cells are exposed to the each of the solutions?
How will you know if a particular treatment is increasing turgor pressure? If it is reducing turgor
pressure?
How could you determine which concentration of each solution is isotonic to the cells?
How do your results compare to your expected results.
AP Biology Diffusion and Osmosis Lab: 4 Name _____________________ Date__________
Procedure 2 – Identifying the Concentration of Sucrose Solutions by their Effects on Potato
Cells
:Design an experiment to:
1) Determine the concentration of unknown solutions of sucrose
2) Calculate the water potential of a yellow and sweet potato cells.
Materials:
 Yellow potato and Sweet potato
 cork borer
 Balances
 Rulers
 Cups




dialysis tubing
Cups
Balances
1M,.8M, .6M,.4M,.2M, 0.0M sucrose
(Your beakers will be color coded)
These questions are just to think about to guide your investigation:
 How can you measure the potato pieces to determine the rate of osmosis?
 How would you determine the molar concentration of the potato.
 How would you calculate the water potential in the cells?
 Is the water potential in the different plants the same?
 What would your results be if the potato were placed in a dry area for several days before your
experiment?
 When potatoes are in the ground, do they swell up with water when it rains? If not, how do you
explain that, and if so, what would be the advantage or disadvantage?
Table that may be useful:
Percent change in mass of dialysis bags
Contents in
dialysis bag
Initial Mass
Final Mass
Mass Difference
Percent Change in mass of potato samples: (sweet and yellow potato)
Percent change
in mass.
AP Biology Diffusion and Osmosis Lab: 4 Name _____________________ Date__________
Contents in
Initial Mass
Final Mass
Mass Difference Percent change
beaker {}
in mass.
Post-lab instructions and questions:
1.
2.
3.
4.
5.
6.
7.
8.
9.
Calculate percent change in mass and graph your data (in your notebook).
Calculate water potential of the potato (in your notebook).
Tell the class what you did to determine water potential of the potato.
Did you change only one variable? If there were any variables unaccounted for, list them.
How can you have a visual representation of your data.
What are the dependent and independent variables in your investigation.
What was your control?
What could you do to improve the experiment?
Was there any unexpected data in your results? Why was this unexpected? Can you figure out
why you got that result?
10. What are other interesting questions that arose from this lab? What might you do next?
11. How would class wide data have an impact in your conclusion of this investigation?
AP Biology Diffusion and Osmosis Lab: 4 Name _____________________ Date__________
AP Biology Diffusion and Osmosis Lab: 4 Name _____________________ Date__________