**CLASS COPY—please don’t take me!** 
Diffusion and Osmosis Lab
PART ONE: DIFFUSION
Introduction: In this lab you will measure diffusion of small molecules through dialysis tubing, an
example of a semi permeable membrane. The movement of a solute through a semi permeable membrane
is called dialysis. The size of the minute pores in the dialysis tubing determines which substance can pass
through the membrane. A solution of glucose and starch will be placed inside a bag of dialysis tubing.
Distilled water and Lugol’s solution will be placed in a beaker, outside the dialysis bag. After 30 minutes
have passed, the solution inside the dialysis tubing and the solution in the beaker will be tested for glucose
and starch. The presence of simple sugars will be tested with glucose test strips and the presence of starch
will be tested with Lugol's solution (iodine-potassium-iodide).
Pre-lab Questions: Answer the following questions in your notebook before you begin the lab.
1. How do you think digested, broken down food molecules get into cells?
2. Draw a picture of the initial lab set-up for this experiment. Be sure to include: glucose, starch,
dialysis tubing, water, and Lugol’s solution.
3. Predict the final results for this lab using a drawing to show your ideas.
Lab Procedure:
1. Obtain a 15-cm piece of dialysis tubing that has been soaking in water. Twist one end of the bag
and fold the twist over. Put a black foam clamp on the folded twist to form a bag. To open the
other end of the bag, rub the end between your fingers until the edges separate.
2. Using a graduated cylinder place 7 mL of the 15% glucose/1% starch solution in the bag. Put a
clamp on the other end of the bag the same way you did in #1, but leave sufficient space for the
expansion of the bag's contents. Record the color of the solution in Table 1.
3. Test the 15% glucose /1% starch solution for the presence of glucose using a glucose test strip. To
do this take your test strip over to the large container of the solution & record the results in Table 1.
4. Fill a 250 mL beaker about 2/3 full with distilled water. Add approximately 15 drops of Lugol's
solution (Iodine) to the distilled water and record the color in Table 1. Test the solution for glucose
using the glucose test strips and record the results in Table 1.
5. Immerse your sealed bag in the beaker of solution and allow your set up to stand for
approximately 30 minutes. While this is sitting you can work on your osmosis application
questions.
6. After the 30 minutes have passed record the final color of the solution in the bag AND the solution
in the beaker in Table 1.
7. Test the liquid in the beaker AND in the bag for the presence of glucose using the test strips. You
will have to open the bag to do this, so be careful not to spill the contents of the bag into the
beaker! Record the results in Table 1.
Answer the following questions on the same sheet of paper you used for the pre-lab questions.
Analysis Questions:
1. Which substance(s) are entering the bag and which are leaving the bag? What experimental
evidence supports your answer?
2. Explain the results you obtained. Include the concentration differences and membrane pore size in
your discussion.
3. Quantitative data uses numbers to measure observed changes. How could this experiment be
modified so that quantitative data could be collected to show that water diffused into the dialysis
bag? Explain.
4. Based on your observations, rank the following by relative size, beginning with the smallest:
glucose molecules, water molecules, IKI molecules, membrane pores, starch molecules.
5. What results would you expect if the experiment started with glucose and IKI solution inside the
bag and only starch and water outside? Explain why you expect this.
Application Questions:
6. Describe how this lab is an analogy (comparison) for how a cell membrane functions.
7. Structurally, how is the dialysis tubing different from a cell membrane?
8. Many molecules that are essential to cells are not able to naturally pass through the phospholipid
molecules of the cell membrane. (They are either too large, charged, or water soluble.) How do
these substances get into our cells if they cannot diffuse through the phospholipids?
9. Describe two ways a semi-permeable membrane could be beneficial for cells.
10. The largest cause of cell death is degradation (damage) of the phospholipids in the cell membrane.
Why do you think a damaged cell membrane is so “fatal” to a cell?
PART TWO: OSMOSIS
Introduction: In this experiment you will use dialysis tubing to investigate the relationship between
solute (the dissolved substance) concentration and the movement of water through a semi- permeable
membrane by the process of osmosis.
Lab Procedure:
1. Obtain four 15-cm strips of presoaked dialysis tubing.
2. Put a clamp on ONE end of each piece of dialysis tubing to form four bags—to do this twist the
end, fold it over, and slip it into the black foam clamp. Carefully label each bag according to the
specified concentrations (i.e., molarities) below. Pour approximately 7 mL of each of the
following solutions into the labeled dialysis bag:
Group A: Distilled water, O.2 M sucrose, 0.6 M sucrose, 1.0 M sucrose
Group B: Distilled water, O.4 M sucrose, 0.8 M sucrose, 1.0 M sucrose
Lab Procedure continues on the next page →
Remove most of the air from the bags by drawing the dialysis bag between two fingers starting
above the liquid and moving your fingers up. Clamp off the other end of the bag the same way you
sealed the bottom (see #2). Be sure to leave sufficient space for the expansion of the contents in the bag!
3. Rinse each bag gently with distilled water (not tap water) to remove any sucrose spilled on the
outside of the bag during filling.
4. Carefully blot the outside of each bag with paper towel.
5. Use the electronic balance to find the initial mass (g) of each bag and record in Table 2.
6. Fill four 250 mL beakers 2/3 full with distilled water.
7. Immerse each bag in one of the beakers of distilled water. Be sure to completely submerge each bag!
8. Let bags soak for at least 30 minutes (possibly overnight).
9. At the end of 30 minutes (or overnight) remove the bags from the water. Carefully blot them dry
with a paper towel.
10. Use the electronic balance to determine the final mass (g) of each bag and record your group's
results in Table 2.
11. Calculate the % change in mass for each bag and record in Table 2.
12. Graph the results for both your individual data and the class average on the graph paper provided.
For this graph you will need to determine the following:
a. The independent variable (x-axis) = _______________
b. The dependent variable (y-axis) = _________________
Answer the following questions on the same sheet of paper you used for Part 1 of this lab.
Analysis Questions:
1. Draw a picture of the 0.6 M sucrose solution when it is initially placed in the water AND a picture
of the 0.6 M solution after it has been soaking for 30 minutes. Depict (show) water and sucrose
molecule concentrations in each picture as well as arrows showing NET water movement.
2. Explain the relationship between the change in mass of dialysis bags and the concentration
(molarity) of sucrose within the dialysis bag. (e.g., The higher the molarity, the ….)
3. Predict what would happen to the mass of each bag in this experiment if all the bags were placed
in a 0.4 M sucrose solution instead of distilled water. Explain your response.
4. Would any water molecules be crossing the dialysis tube’s membrane if we filled a bag with water
and soaked it in water? Explain.
5. Using the graph you constructed, predict the % change in mass of a 0.7 M Sucrose solution placed
in distilled water.
Application Questions:
(Each answer should include a sketch of a cell and a reference to osmosis.)
1. Why are fresh fruits and vegetables sprinkled with water at the grocery store?
2. Roads are sometimes salted in the winter to help melt ice. What effect could the salting have on
the plants along the roadside in the spring? Explain.
3. What might happen to a perch (fish) if it was taken out of a northern Wisconsin lake and placed
into the Atlantic Ocean?
4. Why don’t doctors give patients a distilled water I.V.? (An I.V. is usually filled with a saline (salt)
solution—like tears).
5. As water moves past fish gills, dissolved oxygen in the water diffuses into their blood. This
oxygen transfer is efficient only above certain concentrations of dissolved oxygen in the water. In
other words, oxygen can be present in the water, but at too low of a concentration to sustain
aquatic life. Explain this using what you know about diffusion.
6. Imagine two lakes that are different temperatures (9o C and 15o C), but have exactly the same
oxygen concentration (5ppm). Which lake provides a more “efficient” environment for oxygen
diffusion, the warmer or colder lake? Explain.
Diffusion and Osmosis Lab Data
Table 1--Diffusion Results
Initial Contents
Bag
Beaker
15% Glucose &
1% starch
H2O + IKI
Initial Solution Final Solution Initial Presence Final Presence of
Color
Color
of Glucose
Glucose
yy
v
vvvvvvvvvvvvv v
vv
vv
vvv
vv
Table 2--Dialysis Bag Results: Individual Data
Contents in Dialysis Bag
a). Distilled Water
b). 0.2 M
c). 0.4 M
d). 0.6 M
e). 0.8 M
f). 1.0 M
To Calculate:
% change in mass
=
Initial Mass
Final Mass
e
e
ff
ff
to tt io jk uuh i dd
ri op wnwef gt y ggg
tty uuo kko kki hhh
we seer ti ubp p bbbb
Final Mass-Initial Mass X
Mass Difference % Change in Mass
e
e
ff
fdthuijjjhertttttttt
ddd
dd
ggggg
ggg
ggg
yyu
bobby
bbbb
100
Initial Mass
Table 3--Dialysis Bag Results: Class Data
Bag Contents Group 1 Group 2 Group 3 Group 4 Group 5 Group 6
% change % change
Distilled Water r
0.2 M
0.4 M
0.6 m
0.8 M
1.0 M
er rt ti ed
y
rrrggt h n
n
gggn yh
uj
huh h
ccc c
tag yh
hue du m
Total
% change % change % change % change % change
rr
r
r
rr
g
r
r
r
r
r
r
r
g
g
g
g
g
d
d
d
d
d
d
d
d
d
d
d
d
d
d
d
d
d
d
Class Average
% change
R
R
G
D
D
D