Name: ____________________________________________
Date: __________________________ Section: ______
Diffusion and Osmosis Lab
BACKGROUND
All cells are separated from their external environment by a lipid membrane. Cell membranes regulate the molecular traffic in
and out of the cell. As a result of their structure, membranes are selectively permeable, meaning that certain molecules pass
through the membrane unaided while other molecules are blocked or must use special protein pores to pass through the
membrane. In this lab, we will use dialysis tubing to mimic the cell membrane, and a set of solutions to model environmental
conditions cells encounter.
Questions that result from the above information:
1. How does the size of a solute affect diffusion through the dialysis tubing?
2. How does the concentration of solute affect the rate of diffusion and osmosis?
3. What happens if one solute can pass through the membrane, but another cannot?
Hypotheses to be tested in the lab:
1. Large starch molecules are too large to pass through the selectively permeable membrane, but glucose and iodine
are small enough to pass through the membrane.
2. The concentration of solute on either side of the membrane has no affect on the rate of osmosis because it does not
affect the movement of water.
PART 1: Diffusion Through a Selectively Permeable Membrane
HYPOTHESIS
Large starch molecules are too large to pass through the selectively permeable membrane, but glucose and iodine are
small enough to pass through the membrane.
MATERIALS
 Beaker or cup
 Glucose/starch solution
 Iodine solution
 Distilled water
 Glucose test strips
 Dialysis tubing (12 cm)
 Rubber bands
METHOD
1. Fill a beaker or cup about 1/2 full of water.
2. Use a glucose test strip to test for the presence of glucose in the beaker. Dip the strip into the solution, shake off the
excess liquid, remove immediately, and wait 3 minutes before comparing the color with the scale on the bottle.
Record the concentration in the data table.
3. Add a dropper full or so of iodine solution, enough to make the solution yellow.
4. Take one piece of soaked dialysis tubing and tie one end with a rubber band.
5. When you are ready to fill the dialysis tube, rub the open end of the tube between your fingers to open it up. Use a
pipette to fill about ¾ of the tube with glucose/starch solution.
6. Use one glucose test strip to test for the presence of glucose in the solution you have just put into the dialysis tube.
Record the concentration in the data table.
7. Tie the open end of the dialysis tube, rinse the tube, then place it into the beaker of water and iodine. Label beaker
with group member initials and section #.
Part 1: Diffusion Through a Selectively Permeable Membrane Data Table
Beaker Contents
Beaker Contents
Solution In Dialysis
Color
Glucose Test Strip
Tube Color
(mg/dL)
Start
Dialysis Tube
Glucose Test Strip
(mg/dL)
After 24 hrs.
ANALYSIS
1. Which substance (glucose, iodine, starch) would you infer is the largest? How do you know?
2. Explain how the dialysis tubing acted like a selectively permeable membrane.
3. Explain how diffusion was demonstrated in this experiment. Your answer should include an explanation of how
concentration gradients determined the net direction of solute diffusion across the membrane of the dialysis tube.
PART 2: Osmosis Through a Selectively Permeable Membrane
HYPOTHESIS
The concentration of solute on either side of the membrane has no affect on the rate of osmosis because it does not affect
the movement of water.
MATERIALS
 500 mL plastic cup
 10% sucrose solution
 20% sucrose solution
 Tap water (0% sucrose solution)
 Dialysis tubing (12 cm)
 Rubber bands
 Digital scale
METHOD
1. Obtain 3-500 mL plastic cups per group.
2. Label each cup with cup number (1-3), initials, and section #.
3. Fill cup 1 with about 250 mL of tap water.
4. Fill cup 2 with about 250 mL of 10% sucrose solution.
5. Fill cup 3 with about 250 mL of 20% sucrose solution.
6. Take 1 piece of soaked dialysis tubing and tie one end with a rubber band.
7. When you are ready to fill the dialysis tube, rub the open end of the tube between your fingers to open it up. Use a
pipette to fill about ¾ of the tube with 10% sucrose solution.
8. Tie the open end of the dialysis tube. Rinse and dry the tube.
9. Use the digital scale to weigh the bag as accurately as possible and record in your data table. Place tube in cup 1.
10. Repeat steps 6 through 9 for the other two cups.
11. After 24 hours remove each tube, rinse, dry, and weigh to determine changes in mass over time. Record your data in
your data table.
Part 2: Osmosis Through a Selectively Permeable Membrane Data Table
Dialysis Tubes with 10%
Initial Mass
Final Mass
% Change in Mass
(final g – initial g)/initial g x 100
Sucrose
(g)
(g)
Cup 1: Tube in Water
Cup 2: Tube in 10% Sucrose
Cup 3: Tube in 20% Sucrose
ANALYSIS
1. To which substance(s) (sucrose, water) is the dialysis tube permeable? Not permeable? How do you know?
2. Which cup solution was hypertonic to the interior of the dialysis tube? Hypotonic? Isotonic? Explain.
3. Explain how osmosis was demonstrated in this experiment. Your answer should include an explanation of how
concentration gradients determined the net direction of water diffusion across the membrane of the dialysis tube.