13 Lab Protocol: Diffusion and Osmosis
This lab needs to change – not in the mood
Dialysis tubing allows passage of small but not large solute molecules
- Tie a knot on one end of a strip of dialysis tubing (immersed in water ahead of time)
- Add 3 mL of 1% starch solution strips into the dialysis tubing and tie a knot on the other end. Rinse the bag in water to wash off any starch on the outside of the bag. onin water before immersing the bag into a beaker containing 25 mL of water plus 3 drops of I3KI.
- Incubate for 30 or more minutes and observe the outcome.
Questions:
What was the color of the iodine solution (in beaker) before placement of the dialysis bag? and 30 + minutes after placement of the dialysis bag?
What was the color of the starch solution (in bag) before placement into the beaker?
and 30 + minutes after placement into the beaker?
Explain the results that you observed indicating which molecule(s) was/were able to move through the dialysis tubing.
Using dialysis tubing and a balance (scale) to demonstrate osmosis
- Add 100 mL water to one beaker (label with tape) and 100 mL 5% sucrose to another beaker.
- Prepare 6 dialysis bags (pre-soaked in water) each containing 5 mL of the following solutions (2 each): 1% sucrose, 5% sucrose, 20% sucrose. After tying the second end, immerse each dialysis tube in water for a few seconds one at a time, blot dry on a paper towel, and weigh to the nearest 0.1 g. Record the weight of each tube on a data table.
- Place one bag of each type in each beaker and start a timer. After 15 minutes remove the bags from each beaker, blot dry and weigh.
- Return bags to the proper beakers. After an additional 15 minutes, remove bags from beakers, blot dry and weigh.
Data Table for beaker with water
|
|
Weight at 0 minutes |
Weight after 15 min. |
Weight after 30 min. |
|
1% sucrose |
|
|
|
|
5% sucrose |
|
|
|
|
20% sucrose |
|
|
|
Data Table for beaker with 5% sucrose
|
|
Weight at 0 minutes |
Weight after 15 min. |
Weight after 30 min. |
|
1% sucrose |
|
|
|
|
5% sucrose |
|
|
|
|
20% sucrose |
|
|
|
Questions:
Answer before running procedure:
What is the purpose of weighing the dialysis bags?
What is the purpose of briefly immersing each bag into water at time zero?
How do you think the weight of each bag will change over time?
Data analysis:
Which bag lost the most weight over 30 minutes? Why?
Which bag gained the most weight over 30 minutes?
For this bag, did weight increase more during the first 15 minutes or over the second 15 minutes? Why?
Analysis of osmosis using sheep blood and a microscope
- Measure 1 mL water into one test tube, 1 mL 0.9% NaCl into a second test tube, and 1 mL 5% NaCl into a third test tube.
- Add 2 drops sheep blood to each tube and mix gently.
- Take a drop from each tube and produce a wet mount slide with cover slip.
- Observe each slide under the microscope at 400X magnification.
Questions and observations:
Describe the contents of each tube pointing out differences and similarities.
Describe and photograph the cell shapes on each slide that you observed under the microscope.
Group Project – Determine the concentration of solutes in a plant tissue
Each group is to plan and carry out an independent experiment.
Materials available:
A variety of different plant specimens (each group will choose one). Potato, carrot, apple, celery,
Solutions with different NaCl concentrations
Balance (scale), weigh boat, razor blades, pipets, paper towels, forceps
Groups will collect data in a table over a 30 to 45-minute period and graph their results.
Each group will share their experimental results with the class.
.