Cell Membranes
Activity #4
Which Passes Through a Living Cell's Membrane More Easily, Congo Red Dye Molecules or Water Molecules?
Procedure for Activity #4
- Place a drop of active yeast suspension on a glass slide. Add a coverslip and observe the
yeast cells under low and high power. Make sketches of several cells.
- Place about 1.0 ml of yeast suspension in each of two small test tubes.
- Heat one test tube in boiling water until the CONTENTS have boiled for 30 seconds (perhaps
immersed up to 5 minutes). Allow the tube and contents to cool for a few minutes.
- Add 5 drops of Congo Red dye solution to the boiled yeast suspension and 5 drops to the
unheated suspension.
- Prepare a slide for a sample of each solution and view under the microscope. Observe and note any differences between the appearances of the two solutions of yeast cells.
Data Analysis for Activity #4
- Based on your observations, how would you explain the difference in color of the majority of
cells from each yeast suspension?
- Does killing the yeast cells by boiling disrupt the cell membrane or stop the metabolic
activity of “pumping” material (such as the dye) out of the cell? Is there a way to tell?
- If there are some cells in the nonboiled yeast suspension that are stained red, how would
you explain their presence?
- Which passes through a living cell's membrane more easily, Congo Red dye molecules or water molecules? Utilize your observations to explain.
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