Diffusion and Osmosis Lab
In this lab you will investigate the effects of a selectively permeable membrane on the
diffusion and osmosis between two solutions and the importance of diffusion and
osmosis for cells.
Materials: (per group)
Beaker, Dialysis Tubing, Sucrose Solutions (.2M, .4M, .6M, .8M, 1.0M), Distilled water,
Microscope, Microscope Slide and Coverslip, 15% NaCl Solution, Red Onion
Data/Observation:
Make a table that has 5 columns and 7 rows. Label the first column: Contents in Bag.
Second column: Initial Mass. Third column: Final Mass. Fourth column: Mass
Difference. Fifth column: Percent change in mass. You will use this table to graph
results of the lab.
Analysis Questions:
1. Explain the relationship between the change in mass and the concentration (molarity) of
the sucrose within in the dialysis bags.
2. Predict what would happen to the mass of each bag in this experiment if all the bags
were placed in .4 M sucrose solution instead of distilled water. Explain your response.
3. What is plasmolysis and why did the onion cells plasmolyze?
4. In the winter, grass often dies near roads that have been salted to remove ice. What
causes this to happen?
Procedures:
Part A:
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Obtain a strip of dialysis tubing. One end has already been tied off in a knot for you. Pour 15 mL
of the solution told to you by the teacher. Once this is done. Tie off the other end of tubing. Make
sure to leave space between the liquid in the bag and the knot you tied.
Gently wash the bag with distilled water to remove any excessive sugar from the outside of the
bag. Blot with paper towels. Record the initial mass of your bag and enter this into Table 3. The
remaining information will be filled in as other groups complete this task.
Once all groups are done filling dialysis tubing, all bags will be placed in a container of distilled
water for 30 minutes. After 30 minutes, remove your bag from the container, blot it dry and weigh
the bag to determine the mass. Record data in Table.
Graph data recorded in Table. Remember to Title the Graph, and label the x axis (independent
variable) and the y axis (dependent variable).
Part B:
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Prepare a wet mount slide of a small piece of red onion skin. Place a thin piece of skin on the
slide followed by one drop of distilled water. Carefully place the cover slip over the skin and
water. Using 100x magnification, observe the slide. Sketch and describe the appearance of the
onion cells.
Add several drops of 15% NaCl to one edge of the cover slip. Draw this solution across the slide
by placing a paper towel on the other side of the slip and allow the paper towel to wick the fluid
from the opposite side. Observe the slide. Sketch and describe the appearance of the onion cells.
Remove the cover slip, and flood the area with fresh water. Observe the slide. Sketch and
describe the appearance of the onion cells.