Activity 4: Lab: Making a Wet Mount Slide and Observing Yeast Cells under the Microscope

Materials Needed

Class Demonstration

If needed, the teacher can demonstrate the proper technique for making a wet mount slide. If the teacher has access to a microscope with a camera, the slide that is made can projected for the students to see so they know what to look for when making their own.

Pre Lab Definitions

Methylene blue is used in this activity to visualize the yeast cells. The teacher should explain the unique ability of methylene blue to indicate if the yeast cells are alive or not. Yeast cells that are alive will appear opaque because their enzymes are actively metabolizing or breaking down the methylene blue. Cells that are dead will turn blue because they are unable to metabolize the stain. In addition, the students may be able to see yeast cells on their slides that are undergoing budding- a form of asexual reproduction.

Conducting the Lab

If sufficient microscopes are available, students can independently, or in pairs, make slides from their diluted yeast samples.

First, students will need to place 1 drop or 20 micro liters of methylene blue in a small dish or centrifuge tube. Next, students will use their toothpick to lift a colony of yeast cells off their petri dishes. The cells on the toothpick should be mixed with the methylene blue. After stirring, the tip of the toothpick can be tapped on the microscope slide in order to place a sample of cells. If tapping the toothpick does not yield a sufficient sample, students can use a disposable pipette to place a sample on the slide. A cover slip should then be placed on the sample before viewing under the microscope.

Students can sketch a diagram of the visible cells on their answer sheet. They can also look for cells that are undergoing budding.