Diffusion and Osmosis
Introduction
Solutions consist of solutes (particles) dissolved in a solvent (liquid). In all living organisms there
are many different types of solutes including salts and sugars. The major solvent is water. There
are different concentrations of solutes in various regions of an organism, including differences
between the inside and the outside of the cell.
Living organisms tend towards being in balance, or in equilibrium, with their environment. Cells
achieve this through diffusion. Diffusion is the random movement of solutes from an area of higher
concentration to an area of lower concentration. Osmosis is a special case of diffusion. Osmosis is
the movement of water through a selectively permeable membrane. During osmosis, water
molecules diffuse through the membrane from a region of higher water potential to a region of
lower water potential until equilibrium is reached.
Objective:
Study and understand the processes of diffusion and osmosis.
Materials:
Crystal Violet (molecular weight 394)
Potassium Permanganate (molecular weight 158)
1 Petri dishes with agarose agar
Pipette
Millimeter Ruler
Toothpicks
Potatoes
Cork borer
Paper towels
Balance scale
Sucrose solutions
Plastic cup
Experiment 1: Diffusion
1) Working with your partner, collect one Petri dish with agarose agar.
2) Using a cork corer, make two wells in the agar 3 cm apart from each other. If agar plug
remains, carefully remove with a toothpick.
3) Fill one well with potassium permanganate solution and the other with crystal violet
solution.
4) Very carefully, being sure to keep the dish as flat as possible, place the Petri dishes in a
safe place where it will not be disturbed. Record the time in your lab notebook.
5) Every 15 minutes, measure the diameter of the colored areas to determine the distance
each dye has diffused through the agar and record in your lab notebook. Repeat every
15 minutes for 1.5 hours.
Experiment 2: Osmosis & Diffusion
1. Prepare a stock solution of 1.0 M sucrose by dissolving 86 g of sucrose in 200 ml of
deionized water. Once dissolved add deionized water for a total volume of 250 ml of
1 M sucrose. Use the following table to prepare the remaining solutions.
Table 1 Solute and solvent amounts for different sucrose solutions
Sucrose solution
1.0 M Sucrose solution
Distilled H2O
1.0 M
60 ml
0 ml
0.8 M
48 ml
12 ml
0.6 M
36 ml
24 ml
0.4 M
24 ml
36 ml
0.2 M
12 ml
48 ml
0.0 M
0 ml
60 ml
2. Complete the following steps for each sucrose solution.
3. Pour approximately 60 ml of one sucrose solution into a labeled plastic cup.
4. Use a cork borer (approximately 5 mm in diameter) to cut five potato cylinders for each
test solution. Cut each cylinder to approximately 2 cm in length. Do not include any skin
on the cylinders [Make sure you use the SAME borer for the entire investigation].
5. Calculate the total mass for the five cylinders and record as the initial mass in your lab
notebook. Put the five cylinders into one of the labeled cups containing a sucrose
solution.
6. Repeat steps 3 – 5 for the other sucrose solutions.
7. After each set of potato cores has soaked for 30 minutes, remove the cores from the cup,
blot them gently on a paper towel.
8. Record the final mass and calculate percent change in mass.
Results:
 Complete a properly constructed raw data table for each experiment. The table for
Experiment 2 should look like Table 2 (record ONLY numbers NO units).
 You will need to share your results, from experiment 2, with two other lab groups in order to
have three replicates for each concentration.
Table 2 Mass (g) of potato cores at different sucrose concentrations (+/- 0.1g)
Sucrose
Initial Mass
Final Mass
Change in Mass
concentrations
0.0 M sucrose
0.2 M sucrose
Continue for other concentrations
Processed Data:
Experiment 1:
Graph your data using Excel. You should make a XY (scatter) graph showing lines
for both substances, so that all of the data collected in your table is on the same
graph. Your X-axis (horizontal) should be time in minutes and your Y axis should
be the diameter of the diffusion circle in millimeters.
1.
2.
3.
4.
For each set of points add a trend line.
Add the slope and correlation coefficient for each line.
The slope is the rate of reaction represented by each set of data.
The correlation coefficient indicates the strength of the relationship between time
and diffusion for each stain.
Experiment 2:
Create a processed data table in Excel. Include the average and standard deviation
for each set of values. Graph your data using Excel. You should make a column
graph of your data. Your X-axis should be concentration of sucrose in molarity.
Include standard deviation with your graph.