AP Biology 2012
Tokos/Purdy
Diffusion and Osmosis Lab
Directions: Each pre-lab and post-lab assignment may have a different due date. Please type your answers and submit them on separate paper as they come due.
Pre Lab Questions: Part 1
1. What is the surface area of a cube that measures 1.5 cm on each side?
2. What is the volume of a cube that measures 1.5 cm on each side?
3. Name a physical factor that affects the rate of diffusion and give an example to demonstrate the relationship between surface are and volume.
4. If you had an enormous cube-shaped cell that measured 1.5 cm on a side and a different enormous cell that measured 3 cm on each side, which cell would have the greatest surface are to volume ratio? Which cell would be most successful at meeting all of it’s metabolic needs?
Pre Lab Questions: Part 2
1. Define the terms solute, solvent, and solution.
2. How many grams of sucrose would you add to 100mL of water to prepare a 5 M solution?
3. Write the formula for water potential. What variable does “s” represent? What variable does “p” represent?
4. The water potential of a solution in a dialysis bag depends only on solute potential. Explain why.
5. While holding pressure constant, increasing solute concentration increases or decreases the water potential number (circle one).
6. Circle the correct phrase:
Water will go from an area of -3 water potential to 0.
Water will go from an area of 0 water potential to -3.
7. A dialysis bag contains a sucrose solution of 0.6M. The beaker into which it is placed
has a sucrose concentration of 0.3M. Is the dialysis bag hyper- or hypotonic to the beaker
solution? ______. In which direction is the water expected
to travel? ______Name a sucrose solution concentration that
would be isotonic with the solution in the dialysis bag ______.
8. What is meant by the term “gradient” as it applies to diffusion?
9. Fill in the blanks: water moves across a semi-permeable membrane from an area of
______water potential to an area of ______water potential.
10. Define the term “lysis.”
11. Research the meaning of hyponatremia.
12. Explain why a patient who requires fluid replacement receives a salt solution (saline), not pure water.
Pre Lab Questions: Part 3
1. While holding solute concentration constant, increasing pressure increases or decreases the water potential number (circle one).
2. What is meant by the term “turgid” as it applies to a plant cell?
3. Define turgor pressure.
4. What are the two plant cell structures that help maintain turgor pressure?
5. Define the term plasmolysis.
Post Lab Questions: Part 1
1. How do your results relate to the fact that most cells are small and have cell membranes with many convolutions?
2. Which organelles inside cells have membranes with many convolutions? For one of these examples, explain how this characteristic of structure relates to the function of the organelle.
Post Lab Questions: Part 2
1. Use the terms hypertonic and hypotonic to explain the initial conditions for iodine, glucose and starch in the demonstration.
2. Explain color changes and the results of the glucose test in terms of the structure of the dialysis tubing and the principles of diffusion.
3. Which solute is not expected to reach an isotonic state after extended incubation? Why not?
4. Describe how the results of this demonstration show that dialysis tubing is a reasonable model for cell membranes.
5. Describe on limitation or shortcoming of dialysis tubing as a model for cell membranes.
6. How would increasing the concentration of glucose in the dialysis tubing effect the rate of its diffusion?
7. Do the conditions set up in the demonstration result in a net movement of water? Explain why or why not. What data could we collect to test your prediction?
8. For the class results, which pairs of solutions did not have a net change in mass? Provide an explanation in each case. For one case, support your explanation with a diagram.
9. For the class results, identify one pair of solutions for which the bag increased in mass. Provide an explanation and draw a diagram to support your explanation.
10. For the class results, identify one pair of solutions for which the bag decreased in mass. Provide an explanation and draw a diagram to support your explanation.
Post Lab Questions: Part 3
1. Explain what you would expect to happen if you put salt on watermelon (very yummy). What about salt on slugs in your garden (very cruel).
2. Graph the results for average % change in mass versus solution concentration based on the class data.
3. What concentration of sucrose is iso-osmotic with the plant cell? Explain how you use your graph to arrive at this value.
4. Use the formulas provided in the lab handout and the room temperature you measured to calculate the water potential of the plant cells. Note that the presure potential for the sucrose solution is zero (do you know why….?). Show your work.