Exercise 1: Diffusion – Movement of Solutes across a Membrane
We will be using dialysis tubing to simulate a semipermeable membrane. This tubing allows small molecules (e.g., water, ions, glucose) to pass while preventing large molecules (e.g., macromolecules like proteins, starch, glycogen) from moving across.
Table 1. Results of testing of the dialysis bag and beaker contents at the beginning and end of the Experiment.
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Test for Glucose |
Test for Protein |
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Beginning |
End |
Beginning |
End |
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Dialysis Bag |
Green |
Green |
Violet |
Violet |
|
Beaker |
Blue |
Green |
Clear |
Clear |
Questions:
1. Summarize the results regarding the presence (+) or absence (-) of glucose and protein in the dialysis bag and beaker in Table 2 below:
Table 2.
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Glucose |
Protein |
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|
|
Beginning |
End |
Beginning |
End |
|
Dialysis Bag |
|
|
|
|
|
Beaker |
|
|
|
|
2. Explain the movement or lack of movement of protein and glucose across the dialysis bag membrane?
3. Which solution, that in the bag or that in the beaker, is hypotonic compared with the protein solution?
4. What factors affect the movement of molecules across a semipermeable membrane? Which factor plays the greatest role in biological systems?
5. Briefly explain what active transport is and how it differs from passive transport, especially in terms of concentration gradients.
Exercise 2: Osmosis – The Movement of Water across a Membrane
Before starting, let’s see what you know about the terms hypotonic, isotonic and hypertonic. Examine the diagrams below. Note that the small green circles represent dissolved solutes like salt, glucose, and amino acids. You can assume that the aIDitional space surrounding the solutes is water and that the tan area is INSIDE the cell.
Questions:
1. Define each term below in terms of solute concentration outside compared to the inside of the cell. You donot need to explain which direction water will move (3 pts).
a. Hypotonic –
b. Isotonic –
c. Hypertonic –
2. What concentration of salt is isotonic to animal cells?
3. When cells are in isotonic solution, is there movement of water into or out of the cell? If so, describe this movement.
4. Describe the net movement of water molecules when cells are placed in a hypotonic solution. Explainwhy water moves this way.
5. What happens to an animal cell when placed in a hypotonic solution?
6. What happens to plant cells when placed in a hypotonic solution? What accounts for the difference in outcomes between animal cells and plant cells?
7. Describe the net movement of water molecules when cells are placed in a hypertonic solution. Explain whywater moves this way.
8. Compare and contrast what happens to plant and animal cells when placed in a hypertonic solution. Be sure to use proper terminology.
9. Based on what you learned in this exercise, explain why salt might make a good weed killer.
