Download AP Biology Lab 4: Diffusion and Osmosis

AP Biology Lab 4: Diffusion and Osmosis
PART A: Mystery Solutions
Problem: What is the concentration of the various mystery solutions?
Experimental Set-up:
 6 unknown colored solutions (0M, 0.2M, 0.4M, 0.6M, 0.8M, 1.0M
Sucrose)
 6 potato pieces (cell models)
 Weigh mass of potatoes before/after placing in 75ml of each
mystery solution for 30 min.
 Calculate % Change in Mass
How can you determine the concentration of each solution? Explain
your reasoning.
Data Table:
Solution
Initial
Mass (g)
Final Mass
(g)
% Change in
Mass
100% *(FinalInitial)/(Initial)
Solution
Molarity
Analysis
 Calculate the % Change in Mass of potatoes in each beaker.
 Determine the sucrose concentration in each mystery solution
 Graph the following:
 % Change in Mass of Cell Model vs. Solution Sucrose
Concentrations
Conclusion
How was the data used to determine the sucrose concentration of
unknown solutions? Explain your reasoning.
(Use terms such as hypertonic, hypotonic, diffusion, osmosis, water
potential, etc.)
PART B: Water Potential
Problem: What are the solutions to the following water potential
problems?
 Complete each problem and include in your lab report with full
solutions. Read the BACKGROUND from your manual if you need
help.
1. Calculate the solute potential of a 0.1 M NaCl solution at 25°C. If
the concentration of NaCl inside the plant cell is 0.15 M, which
way will the water diffuse if the cell is placed into the 0.1 M NaCl
solutions?
2. What must the turgor pressure equal if there is no net diffusion
between the solution and the cell?
PART C: Cell Surface Area to Volume Ratio
Problem: Why must cells remain small?
 Using your findings from the SA to Volume ratio worksheet from
the beginning of our cells lesson, write a ½ page summary
explaining the significance of having a high surface are to volume
ratio.
PART D: Lab Simulation and Quiz
Problem: How can your knowledge of osmosis and deffusion be
reinforced?
 Visit the Lab Bench website
http://www.phschool.com/science/biology_place/labbench/lab1
/intro.html
 Complete the entire lab simulation, including all key concepts and
exercises, and take the lab quiz at the end.
 Summarize the concepts, exercises, and analysis and include in
your lab report.
 Print out and turn in your quiz results with your lab report.
PART E: Review Questions
Complete all questions and include them in your lab report.
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. Will water move into or out of a plant cell if the cell has a higher
water potential than the surrounding environment?
7. What would happen if you applied saltwater to a plant?
8. How does a plant cell control its internal (turgor) pressure?
9. Use the principles of osmosis to explain how foods are preserved.