BIO 120L Module Three Lab Report: Diffusion and Osmosis
Experiment 1: Diffusion Through a Liquid
After completing this experiment, record your data in the tables below (Tables 1 and 2).
1. Based on the background information provided regarding the two dyes and general
properties of diffusion, make your prediction about how the diffusion rates of the two dyes
will differ.
2. Next, propose a specific method to test your prediction. Time (sec.)
10
20
30
40
50
60 Structure Table 1: Rate of Diffusion in Corn Syrup
Blue Dye
Time (sec.)
10
20
30
40
50
60 Red Dye Table 2: Speed of Diffusion of Different Molecular Weight Dyes
Molecular Weight
Total Distance
Speed of Diffusion
(mm/hr.) * Blue Dye
Red Dye
* Multiply the total distance diffused by 60 to get the hourly diffusion rate.
3. Which dye diffused faster? Did this support your initial prediction? Why or why not?
4. Does the rate of diffusion correspond with the molecular weight of the dye? Experiment 2: Diffusion—Concentration Gradients and Membrane Permeability
After completing this experiment, record your data in the tables below (Tables 3 and 4).
Table 3: Indicator Reagent Data
Starch Positive
Starch Negative
Glucose Positive
Control (Color)
Control (Color)
Control (Color) Indicator Glucose Negative
Control (Color) IKI Solution
Glucose Test Strip Indicator
IKI Solution
Glucose Test Strip Table 4: Diffusion of Starch and Glucose Over Time
Dialysis Bag After 1 Hour
Beaker Water After 1 Hour 5. Why is it necessary to have positive and negative controls in this experiment?
6. Which substance(s) crossed the dialysis membrane? Support your response with data-based
evidence.
7. Which molecules remained inside of the dialysis bag?
8. Did all of the molecules diffuse out of the bag into the beaker? Why or why not?
9. Does the rate of diffusion change over time? Why or why not? Experiment 3: Osmosis—Direction and Concentration Gradients
After completing this experiment, record your data in the table below (Table 6).
10. For each bag, hypothesize whether water will flow in or out of each dialysis bag, and provide
your reasoning using specific terms from this module.
Yellow:
Red:
Blue:
Green:
Table 6: Sucrose Concentration vs. Tubing Permeability Band Color Sucrose % Initial Volume
(mL) Final Volume
(mL) Net
Displacement
(mL) +/- Yellow
Red
Blue
Green
11. For each of the tubing pieces, identify whether the solution inside was hypotonic,
hypertonic, or isotonic in comparison to the beaker solution it was placed in.
12. Which tubing increased the most in volume? Why?
13. What does this tell you about the relative tonicity between the contents of the tubing and
the solution in the beaker?
14. What would happen if the tubing with the yellow band was placed in a beaker of distilled
water?
15. How are excess salts that accumulate in cells transferred to the bloodstream so they can be
removed from the body? Explain how this process works in terms of tonicity.
16. How is this experiment similar to the way a cell membrane works in the body? How is it
different? Be specific with your response.
17. If you wanted water to flow out of a tubing piece filled with a 50% solution, what would the
minimum concentration of the beaker solution need to be? Explain your answer using
scientific evidence. Experiment 4: Osmosis—Tonicity and the Plant Cell
After completing this experiment, record your data in the table below (Table 7).
Potato Type Potato Table 7: Water Displacement per Potato Sample
Sample
Initial
Final Displacement
Displacement
(mL)—Step 11
(mL)
A
B
A
B Net Displacement
(mL) 18. How did the physical characteristics of the potato differ before and after the experiment?
Did it vary by potato type?
19. What does the net change in the potato sample indicate?
20. Different types of potatoes have varying natural sugar concentrations. Explain how this may
influence the water potential of each type of potato.
21. Based on the data from this experiment, hypothesize which potato has the highest natural
sugar concentration. Explain your reasoning.
22. Did water flow in or out of the plant cells (potato cells) in each of the samples examined?
How do you know this?
23. Would this experiment work with other plant cells? What about with animal cells? Why or
why not?
24. From what you know of tonicity, what can you say about the plant cells and the solutions in
the test tubes?
25. What do your results show about the concentration of the cytoplasm in the potato cells at
the start of the experiment? 26. If the potato is allowed to dehydrate by sitting in open air, would the potato cells be more
likely to absorb more or less water? Explain.
27. Explain why in order to achieve optimal health, physicians advise drinking at least eight
eight-ounce glasses of water per day. List several ways that this helps the body cells function
properly. Why is a diet high in sodium a bad idea when it comes to blood pressure?

 

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