Dialysis and Cells
In this activity, you will use a membrane to construct your own cell model so that you can change
both the internal and external environments. All of our experiments up to this have only allowed us to
manipulate the external environment.
You will use dialysis tubing and several solutions to build your cell model. You will have indicators,
chemicals that show the presence of certain chemicals, to help in detecting what substances can and
cannot pass through your membrane.
Challenge: Develop an explanation for how boundaries and compartments help living systems
maintain and regulate the conditions necessary for life.
Constraints: Your design must:
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Be safe.
Use dialysis tubing.
Use starch suspension.
Use glucose solution.
Use appropriate indicators.
Process
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Brainstorm testable questions about how
membranes affect internal environment of the
cell. Each member of your group must come up
with at least one original question.
With your group, choose the testable question
that you would like to question that you would
like to investigate. Have your teacher approve
your question.
Design an experiment to test the question you
chose.
Have the teacher check and approve your
design.
Create a data table to record a brief summary of
your experimental design and your predictions.
Predict what will happen when you conduct the
experiment, and record this information in the
data table.
Create a data table to record your observations
and results on lab day.
Have the teacher check and approve your
design.
NEED TO KNOW
Background Information
Dialysis tubing is a synthetic membrane, made of a thin,
cellophane-like material. Microscopic pores in dialysis tubing
allow molecules smaller than a certain size to pass through the
membrane.
Glucose is a simple sugar that dissolves readily in water.
Glucose test strips indicate the presence of glucose in
solution by changing color.
Lugol’s iodine solution is an indicator that changes color in
the presence of starch. Use one drop of Lugol’s iodine solution
for every 1 mL of starch suspension: a blue black color
indicates the presence of starch.
Starch is a complex molecule that forms a suspension in
water. Starch turns blue black in the presence of Lugol’s
iodine solution.
The size of a molecule is an important characteristic that
partially determines how the molecules how the molecule
behaves. Chemists have shown that all the molecules of
different substances can vary significantly in size.
Lab day:
WEAR YOUR SAFETY GOGGLES!!!!
1. Set up and conduct your experiment.
2. Be sure to follow all the appropriate protocol for
preparing your cell model for testing.
3. Wash your hands thoroughly.
Analysis
Make a lab report about your experiment.
Include the following:
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A statement of the question you tested and the
results you predicted.
A description of your methods, including the
materials that you used
A description of the results that you obtained,
presented in a well-organized table or diagram
An explanation of your experimental results that
clearly explains how a cell membrane behaves
as a barrier and how the dialysis tubing setup
serves as a model of a cell.
Protocol for Making a Cell Model
For your cell model to work, the membrane must be
the only barrier between the internal and external
environment.
 Rinse all lab equipment with water, and handle the
internal and external solutions for your experiment
carefully to reduce the chance of contamination.
 Obtain a section of dialysis tubing; tie one end of the
tubing securely so that nothing can leak out of the
knot.
 Measure and record the amount of solution you will
add to each cell model in your investigation.
 After carefully pouring the internal solution into
your cell, tie the open end securely to prevent all
leaking.
 Rinse the outside of your cell model to be certain
there is no internal solution present to contaminate
the external environment.
 Blot the cell model dry with a paper towel, and
record its initial mass.
 After conducting your experiment, rinse, dry and
record the cell model’s final mass.