Name
Date
Period
HBiology
Diffusion and Osmosis Lab
NOTE: BE SURE TO ANSWER THE PRELAB QUESTIONS BEFORE COMING TO LAB ON DAY ONE OF
THE EXPERIMENT!!!
Introduction:
Many aspects of the life of a cell depend on the fact that atoms and molecules have kinetic energy and are
constantly in motion. Diffusion and osmosis are two processes exemplifying this principle. Diffusion is the
random movement of molecules from areas of high concentration to areas of low concentration; specifically,
down the concentration gradient. Over time, the molecules will reach equilibrium and there will be no NET
movement of molecules from one area to another. Osmosis is a special case of diffusion. Osmosis describes the
tendency of water to move from an area high in water potential to an area lower in water potential. Osmosis and
diffusion describe transport without the use of cellular energy called passive transport. Another type of
transport, active transport, requires the use of energy because substances are traveling up the concentration
gradient.
Part 1: Diffusion (Demonstration)
In this experiment, we will measure the diffusion of small molecules through dialysis tubing, which will simulate
the plasma membrane in an animal cell. Small solute molecules can travel freely through the selectively
permeable membrane, but larger particles will pass through much slower, or perhaps not at all.
A solution of 1% starch and 15% glucose is placed inside a sealed bag of dialysis tubing which is placed inside a
beaker containing distilled water. Both the solution inside the bag and inside the beaker are tested for the
presence of mono- and polysaccharides using Benedict’s solution and Lugol’s Iodine. After 20-30 minutes, a
sample from both the bag and the beaker are tested again for the presence of monosaccharides and
polysaccharides.
Fill in the ‘Hypothesis’ and ‘Data/Results/Conslusions’ tables as the demo is completed.
Part 2: Osmosis
In this experiment you will use dialysis tubing to investigate the relationship between solute concentration and
the movement of water through a selectively permeable membrane. You will be assigned one of the six
concentrations of solute to perform the experiment. As a class, we will collect and analyze data for all solute
concentrations.
Procedure:
1. Obtain a 30-cm strip of presoaked dialysis tubing.
2. Double knot and tie a string around one end of the dialysis tubing to form a bag. To open the other end, rub
the unknotted end while holding the tubing under running water.
3. Use a syringe to transfer approximately 20-mL of one of the following solutions into the bag. (Your group
will be assigned ONE of the following solutions.)
a. distilled water
c. 0.4 M sucrose
e. 0.8 M sucrose
b. 0.2 M sucrose
d. 0.6 M sucrose
f. 1.0 M sucrose
Remove most of the air from each bag by drawing the dialysis bag between two fingers. Twist, flip and tie
off the other end of the bag. Leave sufficient space for the expansion of the contents in the bag; the
solution should only fill about 1/3 to 1/2 of the piece of tubing.
4. Rinse each bag with distilled water to remove any sucrose spilled during the filling.
5. Carefully blot the outside of each bag and record the initial mass of each bag in grams.
6. Place each bag into an empty 250-mL beaker or cup; label the cup or beaker with the molarity of the
solution in the bag and your names.
7. Fill each beaker or cup with distilled water. Be sure to completely submerge each bag.
8. Let stand overnight. Next period, carefully blot and determine the mass of each bag.
9. Record your group’s data in the table below, filling in only the appropriate row for your molarity. As a class,
we will share and compile data to completely fill in the chart titled ‘Dialysis Bag Results – Group Data’.
Part 3: Water Potential
In this experiment you will be using potato cores in different molar concentrations of sucrose to determine the
water potential of potato cells. Water potential is used to predict the movement of water into or out of plant
cells, in this case, the potato. Water will always move from an area of high water potential (more water
molecules) to an area of lower water potential (fewer water molecules). Movement of water into and out of a
cell is influenced by the amount of solute on each side of the cell membrane. If there are low solute
concentrations in the cell, water moves out of the cell and the cell will shrink. If there are high solute
concentrations in the cell, water moves into the cell and the cell will swell. If high enough solute concentrations
exist outside the cell, the water in the cells (high water potential) will move out of the cell, down the
concentration gradient towards an area where the water potential is much lower.
Procedure:
1. Pour 100 mL of the solution you were assigned in Part 2 into a labeled 250-mL beaker.
2. Use a “corer” to produce four equal sized cores of potato that are approximately 2 cm thick. Do not include
any skin on the slivers.
3. Determine the mass of the four slivers together and record the mass in the table below. Put the four
cylinders in to the beaker of sucrose solution.
4. Cover the beaker with ParaFilm or aluminum foil to prevent evaporation.
5. Let stand overnight. Next period, remove the cores from the beaker, blot them gently with a paper towel
and determine the total mass.
6. Record your group’s data in the table below, filling in only the appropriate row for your molarity. As a class,
we will share and compile data to completely fill in the chart titled ‘Potato Core Results – Group Data’.
OSMOSIS LAB – GROUP DATA
Dialysis Bag Results – Group Data
Contents in Bag
Initial Mass
Final Mass
Mass Difference
% Change in Mass*
Final Mass
Mass Difference
% Change in Mass*
a.) distilled H2O
b.) 0.2 M sucrose
c.) 0.4 M sucrose
d.) 0.6 M sucrose
e.) 0.8 M sucrose
f.) 1.0 M sucrose
Potato Core Results – Group Data
Contents in Bag
Initial Mass
a.) distilled H2O
b.) 0.2 M sucrose
c.) 0.4 M sucrose
d.) 0.6 M sucrose
e.) 0.8 M sucrose
f.) 1.0 M sucrose
Name
HBio: Diffusion and Osmosis Lab
Date
Period
PRE-Lab Questions:
1. What is the dependent variable in this experiment (parts 2 and 3)?
2. What is the independent variable in this experiment (parts 2 and 3)?
3. What is your hypothesis for part 2 (include dependent and independent variables)?
4. What is your hypothesis for part 3 (include dependent and independent variables)?
Part 1: Diffusion (Demonstration)
Hypothesis: (What do you think is going to happen???)
Benedict’s
Inside Bag
Outside Bag
Initial
Final (after 30 minutes)
Iodine
Inside Bag
Outside Bag
Data/Results/Conclusions:
Benedict’s
Inside Bag
Outside Bag
Iodine
Inside Bag
Outside Bag
Final (after 30 minutes)
Part 2: Dialysis Bag Results – Group Data
Contents in Bag
Initial Mass
Final Mass
Mass Difference
a.) distilled H2O
b.) 0.2 M sucrose
c.) 0.4 M sucrose
d.) 0.6 M sucrose
e.) 0.8 M sucrose
f.) 1.0 M sucrose
* % change in mass = [(final mass - initial mass)/initial mass] x 100
% Change in Mass*
Part 3: Potato Core Results – Group Data
Contents in Bag
Initial Mass
Final Mass
Mass Difference
% Change in Mass*
a.) distilled H2O
b.) 0.2 M sucrose
c.) 0.4 M sucrose
d.) 0.6 M sucrose
e.) 0.8 M sucrose
f.) 1.0 M sucrose
* % change in mass = [(final mass - initial mass)/initial mass] x 100
POST-Lab Questions: (Answers to be typed)
1. Graph your data for parts 2 and 3 on two separate graphs. Be sure to graph PERCENT CHANGE IN
MASS as it relates to sucrose molarity. Attach graphs to the lab.
2. For part 2, explain the relationship between the change in mass and the molarity of sucrose within the
bag (not just for your experiment, for ALL data.)
3. Restate your original hypothesis for part 2. Was your hypothesis supported or rejected for part 2?
4. Why did we calculate percent change in mass instead of just the mass of the bags?
5. Predict what would happen to the bags in part 2 if we placed them all into a 0.4M sucrose solution.
Explain.
6. For part 3, explain the relationship between the change in mass and the molarity of sucrose surrounding
the potatoes (not just for your experiment, for ALL data.)
7. Restate your original hypothesis for part 3. Was your hypothesis supported or rejected for part 3?
8. Errors are common in science experiments, especially those which rely on many group’s data. Explain
what errors (at least three) may have occurred within this experiment (not necessarily just YOUR
group, but among everyone). Also explain how these may have affected the data collected in this
experiment.