9.3: Lab Report
LAB REPORT: Diffusion and Osmosis
Part 1 - Exercise 1: Molecular Weight and Diffusion Rate
Employing Steps in the Scientific Method:
- Record the Question that is being investigated in this experiment. ________________________________________________________________
- Record a Hypothesis for the question stated above. ________________________________________________________________
- Predict the results of the experiment based on your hypothesis (if/then). ________________________________________________________________
|
Molecular Weight (g/mole) |
Diameter after 20 min. (mm) |
Diameter after 40 min. (mm) |
Diameter after 60 min. (mm) |
Diameter after 80 min. (mm) |
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|---|---|---|---|---|---|
|
Methylene blue |
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|
Potassium permanganate |
Questions:
- What is the relationship between molecular weight and the rate of diffusion? Explain. ________________________________________________________________
- Go back and look at your initial hypothesis. Does your data support this hypothesis? Explain. _______________________________________________________________
Extension Activity: (Optional)
The results of this experiment can be presented graphically. The presentation of your data in a graph will assist you in interpreting your results. Based on your results, you can complete the final step of scientific investigation, in which you must be able to propose a logical argument that either allows you to support or reject your initial hypothesis.
- Graph your results using the data from Table 1.
- What is the dependent variable? Which axis is used to graph this data? ______________________________________________________________________
- What is your independent variable? Which axis is used to graph this data? ______________________________________________________________________
Part 1 - Exercise 2: Diffusion Across a Membrane
Employing Steps in the Scientific Method:
- Record the Question that is being investigated in this experiment. ________________________________________________________________
- Record a Hypothesis for the question stated above. ________________________________________________________________
- Predict the results of the experiment based on your hypothesis (if/then). ________________________________________________________________
|
Time (min.) |
0 |
5 |
10 |
15 |
20 |
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|---|---|---|---|---|---|---|
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Beaker #1 (water) |
Bag #1 (water) |
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Beaker #2 (water) |
Bag #2 (15% sucrose) |
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Beaker #3 (water) |
Bag #3 (30% sucrose) |
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Beaker #4 (30% sucrose) |
Bag #4 (water) |
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Weight Change (g) |
Time (min) |
Rate (g/min) |
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|---|---|---|---|
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Bag #1 (water) |
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Bag #2 (15% sucrose) |
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Bag #3 (30% sucrose) |
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Bag #4 (water) |
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Appearance of liquid after 20 minutes |
Appearance of liquid after heating |
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|---|---|---|
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Bag #5 (5 mL 30% glucose solution and 5 mL 15% starch solution) |
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Beaker #5 (H2O and 1mL Iodine solution) |
Questions
- Did the weight of each bag (#1 - #4) change significantly over 20 minutes? Explain.
- In which bag(s) was there a net movement of water?
- Explain what is meant by “net movement”.
- Which carbohydrate molecules (glucose, sucrose, starch) were not able to move across the membrane? Explain.
- In terms of solvent (water) concentration, water moved from the area of _______________ concentration to the area of __________________ concentration across a selectively permeable membrane, which is defined as ________________________.
- What can you conclude about the movement of Iodine, glucose, and starch across the dialysis membrane based on your results in Table 3? Support your answers for each with the observation from bag #5 and beaker #5.
- Iodine -
- Glucose -
- Starch -
- We used the dialysis tubing to simulate a cell membrane. How is the dialysis tubing functionally the same as a cell membrane?
- We used the dialysis tubing to simulate a cell membrane. How is the dialysis tubing functionally different from a cell membrane?
Extension Activity: (Optional)
The results of this experiment can be presented graphically. The presentation of your data in a graph will assist you in interpreting your results. Based on your results, you can complete the final step of scientific investigation, in which you must be able to propose a logical argument that either allows you to support or reject your initial hypothesis.
- Prepare a line graph using the data from Table 2.
- What is the dependent variable? Which axis is used to graph this data? ______________________________________________________________________
- What is your independent variable? Which axis is used to graph this data? ______________________________________________________________________
Part 2 - Exercise 1: Observing Osmosis in Potato Strips
Employing Steps in the Scientific Method:
- Record the Question that is being investigated in this experiment. ________________________________________________________________
- Record a Hypothesis for the question stated above. ________________________________________________________________
- Predict the results of the experiment based on your hypothesis (if/then). ________________________________________________________________
Questions
- Which tube contained the limp (flaccid) potato strip? Explain.
- Which tube contained the stiff (turgid) potato strip? Explain.
- Which solution is isotonic to the inside of the potato cell?
- What happened to the potato strip in the isotonic solution?
Part 2 - Exercise 2: Observing Osmosis in Elodea Cells
Employing Steps in the Scientific Method:
- Record the Question that is being investigated in this experiment. ________________________________________________________________
- Record a Hypothesis for the question stated above. ________________________________________________________________
- Predict the results of the experiment based on your hypothesis (if/then). ________________________________________________________________
|
Solution |
Appearance of Elodea Cells |
|---|---|
|
Distilled water (0% NaCl) |
|
|
10% NaCl |
Questions
- Which solution is hypertonic to an Elodea cell? Use your observations to support your answer.
- Would you expect pond water to be isotonic, hypotonic, or hypertonic to Elodea cells? Explain your answer.
- Explain what happens to a plant cell that undergoes plasmolysis.
Part 2 - Exercise 3: Observing Osmosis in Red Blood Cells (Erythrocytes)
Employing Steps in the Scientific Method:
- Record the Question that is being investigated in this experiment. ________________________________________________________________
- Record a Hypothesis for the question stated above. ________________________________________________________________
- Predict the results of the experiment based on your hypothesis (if/then). ________________________________________________________________
|
Test Tube / Solution |
Appearance of Solution |
Can you read print? |
|---|---|---|
|
#1 - Distilled water |
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#2 - 10% NaCl |
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#3 - 0.9% NaCl |
|
Solution |
Appearance of RBCs |
|---|---|
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#1 - Distilled water |
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|
#2 - 10% NaCl |
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|
#3 - 0.9% NaCl |
Questions
- Which solution allowed you to read print through the solution? Explain.
- Which solution is hypertonic to the RBCs? Use your observations to support your answer.
- Which solution is hypotonic to the RBCs? Use your observations to support your answer.
- Which solution is isotonic to the RBCs? Use your observations to support your answer.
Questions for Review
- Define diffusion. What is the energy source for diffusion? Is diffusion considered an active or passive process? Explain.
- Name a molecule that diffused through the artificial membrane (dialysis tubing) that we used in the laboratory. Can diffusion occur without a membrane? Give an example to support your answer.
- What is osmosis? Is it an active or a passive process? Explain.
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Fill in the blank in the following statements.
- A solution that has a lower solute concentration than another solution is said to be ______________________ when compared with the second solution.
- A solution that has the same solute concentration as another solution is said to be ______________________ when compared with the second solution.
- A solution that has a higher solute concentration than another solution is said to be ______________________ when compared with the second solution.
- What does it mean when a membrane is selectively permeable?
Practical Challenge
-
Briefly explain what happens to a red blood cell when placed into the following solutions.
- Isotonic solution –
- Hypertonic solution –
- Hypotonic solution -
- The concentration of glucose inside Elodea cells is 5 mM. What is the solution in moles (M)? What will happen to an Elodea cell if it is placed in a 1 M glucose solution? Explain.
- Apply what you learned in the lab to explain why it is said that marine organisms, which live in saline environments, literally live in a desert environment.