Passive Transport Inquiry

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Passive Transport Inquiry
Lab Group Names: _____________________________________________________________________
Background knowledge:

Dialysis tubing is an artificial selectively permeable membrane. You will use this tubing to create
a model cell.
o What does it mean to be selectively permeable?

You will be filling your cell with a glucose/starch solution. Then submerging your cell in a water
/ iodine solution.
o What do you know about the size of glucose in relation to the size of starch?
o

What occurs when you mix starch and iodine? If you don’t know, try it… take 2 mL of
glucose /starch solution and add 5 drops of iodine. What happened?
Glucose can be detected using a glucose test strip. To use a glucose test strip, you dip the strip
into the solution you want to test then you wait 2 to 3 minutes. If glucose is present, the
indicator box will change color to a deep dark green. If glucose is not present, no color change
will occur.
o How could you use these test strips to determine if glucose was able to pass through the
dialysis tubing?
Objectives:

Demonstrate osmosis and diffusion of molecules through a selectively permeable membrane

Determine which molecules are able to pass through a membrane and which molecules are not
able to pass
Prediction:
Given what you know about iodine and starch, how will you know if the starch moves out of the cell or
the iodine moves into the cell?
Given what you know about glucose test strips, how will you know if the glucose moves out of the cell?
How will you know if water was able to move from the cup into your cell model?
Predict what will happen when you place 15 mL of glucose/starch solution into a dialysis tubing cell
model then submerge your model in a water/iodine solution.
Lab Procedure Day 1:
1. Fill a beaker with 150 mL of tap water. Test this water for glucose. Record your findings.
2. Add 20 to 25 drops of iodine to the beaker of water. Record the color of the liquid.
3. Obtain 15 mL of glucose/starch solution. Dip a glucose test strip in the solution. Record your
findings.
4. Obtain a piece of dialysis tubing. Tie a knot in one end. Gently rub the other end between your
fingers to open it. Stick a funnel in the opening and add 15 mL of glucose / starch solution.
Record the color of the liquid.
5. Tie off the other end – be sure to leave space for substances to move into or out of your cell
model. Rinse off the the cell model. Pat dry with a paper towel. Obtain the mass of your cell
model. (Place a weigh boat on the scale, press the tare button, and place your cell in the weigh
boat.) Record your findings.
6. Place your cell model in the beaker containing the water/iodine solution.
7. Label your beaker and set it aside until tomorrow….
Data Table
Characteristic
Solution in Beaker
Cell Model
Initial color
Final color
Initial glucose test strip
Final glucose test strip
Initial mass
N/A
Final mass
N/A
Initial contents
Final contents
Lab Procedure Day 2:
1. Remove your cell model from the beaker. Place your model on a paper towel. Record the final
color of the solution in the beaker and the final color of your cell model.
2. Obtain a final mass for your cell model. Record your findings.
3. Test the solution in the beaker for glucose. Record your findings.
4. Carefully cut open the cell model and test the solution for glucose. Record your findings.
5. All liquids can be disposed of in sink. Rinse out the beaker and return it to the cabinet. Test
strips and dialysis tubing go in the trash can.
Data Analysis:
1. What is diffusion?
2. What is osmosis?
3. Did osmosis occur with respect to the model cell? What observation led you to this conclusion?
4. Did the glucose molecules pass through the dialysis tubing? How do you know?
5. Did the starch molecules pass through the dialysis tubing? How do you know?
6. Did the iodine molecules pass through the dialysis tubing? How do you know?
7. Was the dialysis tubing selectively permeable? Explain / support your answer using the data you
obtained.
8. What are two characteristics of substances that do not allow them to pass through the
semipermeable membrane of living cells?
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