Diffusion Dialysis Tubing Lab
Academic Biology
Name: __________________________________________ Period: _______________
Diffusion Dialysis Tubing Lab
Purpose: In this lab, you will observe the diffusion of a substance across a semipermeable membrane. Iodine will be used as a known indicator for the presence
of starch in a solution.
Pre-Lab: Define the following terms:
 Hypertonic –
 Hypotonic –
 Concentration gradient –
 Diffusion –
 Osmosis –
 Selectively or semi permeable –
 Indicator –
Procedure:
1. Wet and open the dialysis tubing. Tie a knot in the bottom.
2. Add equal amounts of water and cornstarch. Tie the top.
3. Fill a plastic cup halfway with water and add ten drops of iodine.
4. Place the dialysis tubing in the cup so that the cornstarch mixture is submerged in the iodine/water
mixture.
5. Record your observations after 15 minutes and 24 hours in the data table.
6. While you are waiting, complete the predictions and questions sections below.
Prediction Questions:
Iodine can be used as to indicate the presence of starch. It will turn the starch grains a dark purplish color.
 If starch could cross the dialysis tubing, what color would the water in the beaker turn?
 If iodine could cross the dialysis tubing, what color would the water in the dialysis tubing turn?
 If both iodine and starch could cross the dialysis tubing, what color changes would you observe?
Diffusion Dialysis Tubing Lab
Academic Biology
Procedural Questions:
1. Molecules tend to move from areas of ___________ concentration to areas of _____________
concentration.
2. What is the main difference between diffusion and osmosis?
3.
The dialysis tubing in this procedure could be compared to what part of the cell?
4.
Does the dialysis tubing or the cup contain a higher concentration of starch?
5.
Does the dialysis tubing or the cup contain a higher concentration of iodine?
6.
Which solution is hypertonic for iodine?
7. Which solution is hypotonic for iodine?
Pictures for observations:
starting
after 15 minutes
after 24 hours
Data Table:
Solution
Solution
Solution
Solution
in
in
in
in
my cup
my dialysis tubing
demo beaker
plastic baggie
Starting Color
Color after 15 mins
Color after 24 hrs
xxxxxxxxxxxxxxxxxxx
xxxxxxxxxxxxxxxxxxxx
xxxxxxxxxxxxxxxxxxxx
xxxxxxxxxxxxxxxxxxx
xxxxxxxxxxxxxxxxx
xxxxxxxxxxxxxxxxxxx
Data Analysis:
1. Based on your observations, which substance moved, the iodine or the starch? How do you know?
2.
Is the dialysis tubing selectively permeable? How do you know?
Diffusion Dialysis Tubing Lab
Academic Biology
3.
To which substance was the plastic bag permeable? How do you know?
4.
Sketch the cup and dialysis tubing in the space below. Use arrows to illustrate how diffusion
occurred in this lab.
5.
What would happen if you did an experiment in which the iodine solution was placed in dialysis tubing
and the starch solution was in a beaker? Be detailed in your description and be sure to describe color
changes and the direction of flow of the molecules.