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AP Biology
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Lab Partner __________________ Table ___
Investigation 4: DIFFUSION AND OSMOSIS
Big Idea 2: Cellular Processes: Energy and Communication
PRELAB: Be ready to answer the following questions: (any could be found on the written portion of
your exams)
1. What is kinetic energy and how does it differ from potential energy?
2. What environmental factors affect kinetic energy and diffusion?
3. Why do these factors alter diffusion rates? How do they affect rates?
4. How are gradients important in diffusion and osmosis?
5. What is the explanation for the fact that most cells are small and have cell membranes with many convolutions
6. What is the equation used to calculate water potential? (Be sure to describe the two components that are used to
calculate it.) Why type of experiment could you design to identify the water potential of a carrot? (or other plant)
7. Will water move into or out of a plant cell if the cell has higher water potential than the surrounding environment?
8. What would happen if you applied saltwater to a plant?
9. How does a plant cell control its internal (turgor) pressure?
PROCEDURE 1: Surface Area and Cell Size
Step 1:
1. Which solution is an acid? ___________
2. Which solution is a base? ___________
3. What color is the dye in the base? ___________ In the acid? ___________
Step 2:
Helpful equations:
Surface Area: 6a2 (a = length of one side of a cube)
Volume: a3
% Penetrance = Penetrated Volume (total volume minus remaining volume)/Total Volume
Cut three cubes: 1cm per side, 2cm per side and 3 cm per side of the alternative colored gelatin. You will be
using white vinegar in place of the 0.1M HCl
Table 4.1 Date ___/___ Time ___:___
BEFORE
AFTER
Surface Area
Total Volume
Surface Area to
Remaining
% Penetrance
Cube Sides
Volume Ratio
Volume
1 smallest:
2 middle:
3 largest:
1. Which block had the greatest % penetrance? ___________
2. How do you explain the differences?
PROCEDURE 2: Modeling Diffusion and Osmosis
1. Why would it be important for an IV solution to have salts in it instead of pure water?
2. How can you use weights of the filled cell models to determine the rate and direction of
diffusion?
AP Biology Investigation 04: 1
3. What would be the appropriate control for question #2?
Steps 1-4:
You will choose three pairs of solutions (instead of four) and our 4th tube will be water/water pairing. Make one
of your pairings be two 1M solutions ~ with one of those solutions being 1M NaCl.
Table 4.2 Date ___/___ Time ___:___
Pairing Tube Sol’n Cup Sol’n
Prediction of
Initial Weight
Final Weight
% Change
tube weight (+/-)
1
2
3
4
Water
Water
No change
1. Which pair(s) that you tested did not have a change in weight? How can you explain this?
2. Explain the results of the pairing with the two 1M solutions.
3. Does the protein solution have a high molarity? What is evidence for your conclusion? (If you did not
use albumin in your pairings, consult the data from a group that did.)
4. How could you test for the diffusion of glucose?
5. How is the dialysis tubing functionally different from a cellular membrane?
PROCEDURE 3: Observing Osmosis in Living Cells
1. What would happen if you applied saltwater to the roots of a plant? Why
2. Will water move into or out of a plant cell if the cell has a higher water potential than its
surrounding environment?
Step1: Put a drop of distilled water on the slide, the a single leaf, then bring the edge of the cover slip at an
angle to the edge of the water, slowly lower coverslip to avoid air bubbles. Before you look at the slide, record
your prediction in Table 4.3
1. Where is the cell membrane in relation to the cell wall?
AP Biology Investigation 04: 2
2. Can you see the two structures easily? Why or why not?
3. What parts of the cell that you see control the water concentration inside the cell?
4. What changes would you expect to see when plant cells are exposed to the solutions in Procedure #2?
Step 2:
Table 4.3 Date ___/___ Time ___:___
Plant Cell in
Prediction
Solution of:
Distilled water
Results
Designing and Conducting Your Own Investigations:
Part 1: Identify the concentrations of various sucrose solutions. There are five different colored solutions.
From what you have learned so far, design and conduct an experiment to identify which color is the: 0.2M, 0.4M,
0.6M, 0.8M and 1.0M solution.
Include the following in a one page typed paper: A. Hypothesis, B. Procedures (simplified), C. Data table
(with the control and the independent/dependent variable(s) indicated) and D. Conclusions.
You may include your name and your lab partner’s name on the typed paper, one turn-in if you complete
the write-up together.
SKETCH OUT YOUR GENERAL PROCEDURES BELOW:
Part 2: Determine the water potential, Ψ = ΨS + ΨP, of a carrot or other plant. Strong suggestions: use the
sucrose solutions above to identify the molarity (C) where the carrot’s net osmosis rate is close to zero. (I would
graph the results to predict the most accurate molarity.) Use the molarity (C) identified to calculate the solute
potential (ΨS=-iCRT) and ultimately the water potential. HINT: the pressure potential, ΨP, will be zero when the
osmosis rate is close to zero. Your “partner” typed paper should include the same components (A-D) listed in
Part 1 above.
SKETCH OUT YOUR GENERAL PROCEDURES BELOW:
AP Biology Investigation 04: 3