Pre-Lab: A Cell Model
Lesson Target
• I can explain how boundaries and
compartments help living systems maintain
and regulate the conditions necessary for life.
Vocabulary
• Indicators- Chemicals that show the presence
of certain chemicals, to help in detecting what
substances can and cannot pass through the
membrane.
• Protocol- Steps for carrying out an
experiment- PROCEDURES
Vocabulary
• Dialysis Tubing- A synthetic membrane made
of a thin cellophane-like material.
Microscopic pores allow certain sized
substances to pass through.
• Glucose- a simple sugar that readily dissolves
in water.
Vocabulary
• Lugol’s Iodine solution- an indicator that turns
blue-black in the presence of starch.
• Starch- A complex molecule that forms a
suspension in water. Turns blue-black in the
presence of iodine.
• Benedicts Solution- A second test for glucose.
Turns orange when heated.
Testable Question
• How does the size of a molecule affect its
ability to pass through a membrane?
Hypothesis
• The smaller molecule will be able to pass
through the membrane more easily than the
larger molecules, because the membranes
pores need to be small to help regulate what
substances can pass through the membrane in
order to protect the cell.
Materials List
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Safety goggles
Plastic pipettes
Dialysis tubing
Plastic cups
Starch solution
Glucose solution
Distilled water
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Lugol’s Iodine solution
Glucose test strips
Graduated cylinder
Permanent marker
Tubing clamps
Paper towels
Benedicts solution
Variables
• MV- The internal/ external environment of the
“cell”
• RV- The passage of molecules across the
membrane.
• CV’s- Amt. of solution in each model; Amt of
solution in each environment; time allowed in
each environment…etc.
Procedures- Day 1
1. Wet the strip of dialysis tubing and tie a knot
or use a clamp to secure one end of the tube.
2. Measure out the correct amt. of solution for
the inside of the tube. Use the pipette to fill
the tube.
3. Tie or clamp the second end of the model.
Rinse and dry the model.
4. Mass the model and record in data table.
Procedures
5. Fill one cup with the proper amt. of solution
for the external environment. Label cup with
NAMES, DATE, and PERIOD.
6. Place your model in the cup
7. Clean up your work station. Sanitize the
counter, wash and dry all equipment. Wait at
lab station for inspection.
Procedures- Day 2
8. Take model out of cup. Rinse, dry, and record
mass of model.
9. Test external environment for the presence
of the cells internal solution using the
appropriate indicator
EX.- if starch was on the inside of the cell model use
Lugol’s iodine to test the external environment for
the presence of starch solution.
Procedures- Day 2
10.Carefully open the contents of the cell model
over a clean cup. Test the internal solution
for the presence of the cell model’s external
environment.
EX. If glucose was used on the outside of the cell
model use the glucose test strips or Benedicts to test
for the presence of glucose. Record the data in the
table.
Procedures- Day 2
11. Clean and sanitize your work station. Wait
at your lab station for inspection.
Results/ Data
Table 1. Data for cell model constructed using dialysis tubing
Contents of internal environment
Contents of external environment
Initial mass (g)
Final Mass (g)
Change in Mass (g)
Predicted changes with explanations
Internal Environment
External Environment
Conclusion
Write a conclusion that addresses the following:
• A statement of the question you tested and the results
you predicted
• A description of your methods (how did you preform
the experiment- including the materials you used.
• A description of your results in a well-organized table.
• An explanation of your experimental results that
clearly explains how a cell membrane behaves as a
barrier and how dialysis tubing serves as a model of a
cell.