Compare and contrast diffusion and osmosis.
Student Name: OLUCHUKWU ONOVO
Access Code (located on the lid of your lab kit): ACCESS CODE -UNW5JD4
Pre-Lab Questions:
1. Compare and contrast diffusion and osmosis.
2. What is the water potential of an open beaker containing pure water?
3. Why don’t red blood cells swell or shrink in blood?
Experiment 1: Diffusion through a Liquid
Table 1: Rate of Diffusion in Corn Syrup
Time (sec) Blue Dye Red Dye
10 1/4 1/2
20 1/2 1
30 5/8 1 1/4
40 7/8 1 3/8
50 1 1 1/2
60 1 1/8 2
70 1 1/8 2 1/4
80 1 1/8 2 3/8
90 1 1 /4 2 1/2
100 1 3/8 2 1/2
Time (sec) Blue Dye Red Dye
110 1 3/8 2 3/4
120 1 1/2 2 7/8
Table 2: Speed of Diffusion of Different Molecular Weight Dyes
Structure
Molecular Weight Total Distance Traveled (mm) Speed of Diffusion (mm/hr)*
Blue Dye 792.844g/mol 38.1 1143mm/hr
Red Dye 496.416g/mol 73.025 2190.75mm/hr
*To get the hourly diffusion rate, multiply the total distance diffused by 30.
Post-Lab Questions
1. Examine the plot below. How well does it match the data you took in Table 1?
2. Which dye diffused the fastest?
3. How does the rate of diffusion correspond with the molecular weight of the dye?
4. Does the rate of diffusion change over time? Why or why not?
Experiment 2: Diffusion – Concentration Gradients and Membrane Permeability
Table 3: Indicator Reagent Data
Indicator
Starch Positive Control (Color)
Starch Negative Control (Color)
Glucose Positive Control (Color)
Glucose Negative Control (Color)
Glucose Test Strip
n/a
n/a
IKI
n/a
n/a
Table 4: Diffusion of Starch and Glucose Over Time
Indicator
Dialysis Bag After 1 Hour
Beaker Water After 1 Hour
Glucose Test Strip
IKI
Post-Lab Questions
1. Why is it necessary to have positive and negative controls in this experiment?
2. Which substance(s) crossed the dialysis membrane? Support your response with data-based evidence.
3. Which molecules remained inside of the dialysis bag?
4. Did all of the molecules diffuse out of the bag into the beaker? Why or why not?
Experiment 3: Osmosis – Direction and Concentration Gradients
Hypothesis: The data sheet
Table 6: Sucrose Concentration vs. Tubing Permeability
Band Color
Sucrose % Initial Volume (mL) Final Volume (mL) Net Displacement (mL)
Yellow 30% 10ml 14ml 4ml
Red 15% 10ml 12ml 2ml
Blue 3% 10ml 10ml 0
Green 3% 10ml 3ml 7ml
Post-Lab Questions
1. 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.
2. Which tubing increased the most in volume? Why?
3. What does this tell you about the relative tonicity between the contents of the tubing and the solution in the beaker?
4. What would happen if the tubing with the yellow band was placed in a beaker of distilled water?
5. Osmosis is how excess salts that accumulate in cells are transferred to the blood stream so they can be removed from the body. Explain how this process works in terms of tonicity.
6. How is this experiment similar to the way a cell membrane works in the body? How is it different? Be specific with your response.
7. 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
Table 7: Water Displacement per Potato Sample
Potato
Potato Type and Observations
Sample
Initial Displacemen t (mL)
Final Displacement (mL)
Net Displacement (mL)
1
1A
1
1B
2
2A
2
2B
Post-Lab Questions
1. How did the physical characteristics of the potato vary before and after the experiment? Did it vary by potato type?
2. What does the net change in the potato sample indicate?
3. Different types of potatoes have varying natural sugar concentrations. Explain how this may influence the water potential of each type of potato.
4. Based on the data from this experiment, hypothesize which potato has the highest natural sugar concentration. Explain your reasoning.
5. Did water flow in or out of the plant cells (potato cells) in each of the samples examined? How do you know this?
6. Would this experiment work with other plant cells? What about with animal cells? Why or why not?
7. From what you know of tonicity, what can you say about the plant cells and the solutions in the test tubes?
8. What do your results show about the concentration of the cytoplasm in the potato cells at the start of the experiment?
9. 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.
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