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% *(Final-Initial)/(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.