Lovejoy High School
Unit Name: Cellular Processes
PreAP Biology
Lab: Cell Transport
TEKS: 4B investigate and explain cellular
processes, including homeostasis, energy
conversions, transport of molecules, and
synthesis of new molecules
Learning Goals: What does the term selectively
permeable mean and what effects does it have on
cell transport?
Teacher Management
Estimated Time for Completion: Day one is 30-45 minutes with a solid explanation of lab, set up and
time to discuss pre-lab questions. 15-45 minutes for the second day, allowing time for the questions to be
answered.
Introductory Statement:
In this lab, students will:
a) Design an experiment to determine whether diffusion occurs across a plastic membrane
b) Interpret the results to determine whether the plastic bag is selectively permeable
c) Analyze results and compare them to the cell membrane
Materials:
400 mL Beakers/Plastic cups
Graduated cylinders
Starch solution
Dialysis Tubing
Iodine solution
Masking tape
Triple beam balance
String
Reference information:
http://www.wisc-online.com/objects/ViewObject.aspx?ID=AP11003
http://www.wiley.com/legacy/college/boyer/0470003790/animations/membrane_transport/membrane_trans
port.htm
http://programs.northlandcollege.edu/biology/Biology1111/animations/transport1.html
https://www.youtube.com/watch?v=2Th0PuORsWY&feature=related
Engaging Focus:
Discussion on what happens when starch comes in contact with iodine. Show them an example of the color
change. Websites are referenced above for demonstrations on cell transport.
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Experience:
Students will work in groups.
Teacher Prep:
You will need to make or purchase a starch solution and have prepared Iodine dropper bottles. Clear plastic
cups work well instead of the beakers and can be thrown away after the lab. The dialysis tubing needs to be
pre-soaked for about 20 minutes. String or dental floss work to tie off the dialysis tubing. We like to use
iodine on the outside and starch on the inside but can be switched if needed.
Procedure:
1. Remove the dialysis tubing from the beaker and prepare for filling by tying one end and opening
the other by rubbing it together between your thumb and index finger. (Make sure and explain to
students what will happen if it is not tied securely.)
2. Fill the tube with approximately 10 ml starch solution. There should be open space in your tube
(the starch solution should NOT fill the tube entirely).
3. Tie open end of tube to seal. Rinse the tube to remove any starch solution from the outside of
the bag.
4. Weigh tube and record in data table
5. Weigh the empty beaker or cup.
6. Fill beaker (or cup) with 250 ml of iodine solution (250 ml water and 20 drops iodine) and
weigh. Subtract that weight from empty weight to obtain weight of iodine solution and record in
data table
7. Record initial color of solution in tube and in beaker/cup and record in data table (The solution in
the cup should be an amber-brown color, and the solution in the tube should be white)
8. Submerge tube in iodine solution for 24 hours (Teacher will need to place in a dark location for
the duration)
After 24 hours (If class is longer, it will work within the same day)
9. Remove tube from iodine solution and record color and weight of tube and solution of beaker in
data table
10. Pour iodine solution down the drain and rinse beaker. Throw tube away. Make sure your lab
table is clean and dry. Now go sit down at your desk to finish the rest of this lab.
Synthesis:
Will the polyethylene membrane allow iodine to cross the membrane? Will the polyethylene membrane
allow starch, which is a larger molecule than iodine, to cross the membrane?
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Cell Transport Lab
Lovejoy HS Biology
Learning Goal: What does the term selectively permeable mean and what effects does it have on cell transport?
TEK-4B investigate and explain cellular processes, including homeostasis, energy conversions, transport of
molecules, and synthesis of new molecules
Problem:
Will the polyethylene membrane allow iodine to cross the membrane? Will the polyethylene membrane allow starch,
which is a larger molecule than iodine, to cross the membrane?
Helpful websites about Transport:
http://www.wisc-online.com/objects/ViewObject.aspx?ID=AP11003
http://www.wiley.com/legacy/college/boyer/0470003790/animations/membrane_transport/membrane_transport.htm
http://programs.northlandcollege.edu/biology/Biology1111/animations/transport1.html
https://www.youtube.com/watch?v=2Th0PuORsWY&feature=related
Pre- Lab Questions
1. What type of molecule is starch and what is the monomer of starch?
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2. Iodine is a testing indicator for the presence of starch. According to the results in our biochemical lab, what
happens when iodine mixes with starch?
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3. What does it mean to be selectively permeable or semi-permeable?
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4. Describe the structure of the cell membrane.
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5. Define diffusion.
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]
6. What is the difference between diffusion and osmosis?
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7. In passive transport, molecules tend to move from areas of ______________ concentration to areas of
_____________ concentration.
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LAB
Hypothesis
 Formulate a hypothesis that predicts the movement of water, starch and iodine across the plastic membrane.
Use the If.., then…, because format.
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_____________________________________________________________________________________________
_____________________________________________________________________________________________
Objectives:
In this biolab, you will:
a) Design an experiment to determine whether diffusion occurs across a plastic membrane
b) Interpret the results to determine whether the plastic bag is selectively permeable
c) Analyze results and compare them to the cell membrane
Materials:
400 mL Beakers/Plastic cups
Graduated cylinders
Starch solution
Dialysis Tubing
Iodine solution
Masking tape
Safety Iodine is poisonous if large amounts are ingested. Keep it away from your face, and wash your hands
thoroughly after using it. Iodine will stain your hands and clothing, so be careful not to spill it. Handle glass
objects carefully. If they break, tell the teacher. Do not pick up broken glass.
Procedure:
11. Remove the dialysis tubing from the beaker and prepare for filling by tying one end and opening the other
by rubbing it together between your thumb and index finger.
12. Fill the tube with approximately 10 ml starch solution. There should be open space in your tube (the
starch solution should NOT fill the tube entirely).
13. Tie open end of tube to seal. Rinse the tube to remove any starch solution from the outside of the bag.
14. Weigh tube and record in data table
15. Weigh the empty beaker or cup.
16. Fill beaker (or cup) with 250 ml of iodine solution (250 ml water and 20 drops iodine) and weigh. Subtract
that weight from empty weight to obtain weight of iodine solution and record in data table
17. Record initial color of solution in tube and in beaker/cup and record in data table
18. Submerge tube in iodine solution for 24 hours
After 24 hours
19. Remove tube from iodine solution and record color and weight of tube and solution of beaker in data table
20. Pour iodine solution down the drain and rinse beaker. Throw tube away. Make sure your lab table is
clean and dry. Now go sit down at your desk to finish the rest of this lab.
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Data Table
Initial Color
Initial Weight (g)
Final Color (after 24
hours)
Final Weight(g)
Change in Weight(g)
Solution in
Beaker/Cup
__________
Solution in
Tubing
__________
Analysis
1. Diagram- Draw a picture of the set up before and after. Label the diagram and indicate the direction of diffusion.
2. Graph (of Weights Before and After) Graph must include a proper title and axis labels.
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Questions: Answer the questions based on your results and knowledge of the content.
1. Does your data support your original hypothesis? Explain why or why not.
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2. Based on your observations, which substance moved, the iodine, starch or both?
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3. How did you determine this?
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4. The plastic baggie was permeable to which substance?
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5. Is the plastic baggie selectively permeable? Why or Why not?
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6. Based on your results is it a good idea to store iodine in a plastic bag? Explain.
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7. Compare the plastic bag to the cell membrane.
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8. Cell membranes contain small holes, or pores. Pore size may determine why some chemicals can or cannot
pass through a cell membrane. How might the size of the membrane pores compare to the size of the iodine
molecules? Explain.
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9. How might the size of the membrane pores compare to the size of the starch molecules? Explain.
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10. Conclusion: Critique your experiment. What could have you done differently to get better results? Was there
error in your data? If you got invalid results, why? Etc.
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11. Conclusion: What can you infer from this experiment about movement of large and small molecules through a
thin polyethylene membrane? How does this relate to the cell and its cell membrane? (minimum of 4
sentences)
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