Lab Sheet
Burping Yeast
Objective:
 Determine the effect of temperature on the cellular respiration of yeast.
 Practice pipetting skills
IMPORTANT: Read the background and procedure then do the pre-lab questions before
performing the experiment.
Background:
All living things carry on the process of cellular respiration. Respiration that occurs in the
presence of glucose is called aerobic while respiration that occurs without oxygen is anaerobic.
During respiration food, usually in the form of glucose, is broken down by a series of chemical
reactions. As the glucose is broken down the cells transfer its energy to a molecule called ATP,
or adenosine triphosphate. Cells use ATP as energy for the numerous chemical reactions that
occur in the cell.
Respiration rate depends on several environmental factors. In this laboratory activity one of these
factors, temperature, will be investigated in yeast cells. Yeasts are eukaryotic, unicellular fungi
that are commercially important. They are necessary for the production of bread, wine, beer, and
industrial chemicals. As the cells carry on cellular respiration they will break down glucose and
release carbon dioxide and water. The rate of respiration in yeast will be measured by counting
the number of carbon dioxide bubbles released.
Materials:
2 600 ml beakers (or other appropriate container for water bath)
ice
thermometer
2 25mm x 200mm test tubes
2 disposable pipettes
2 metal hex nuts
p1000 micropipettor
yeast solution
glucose solution
stopwatch
Procedure:
1. Set up two water baths—warm (30-40 C) and cold (5-10 C) in large beakers.
Make sure the water is almost to the top of the beaker.
2. Fill a TALL test tube with water from the beaker and leave it in the beaker. Make
sure you use the water from the water bath so it will be at the appropriate
temperature.
3. Using plastic droppers mix 500 ul of yeast solution and 500 ul of glucose solution in a
microcentrifuge tube. To avoid contamination be sure to use clean tips for each
solution.
Lab Sheet
4. It is important that you get all of the yeast-glucose solution in the bulb of the dropper.
Follow these steps:
 use a clean dropper
 completely depress the bulb of the dropper
 slowly suck up all the yeast-glucose
 flip the dropper upside down
 release the bulb to draw the liquid down into the bulb
5. Slide a metal nut over the shaft of the dropper as shown in Figure 1
6. Slowly lower the dropper into the test tube and put the test tube into the water bath.
7. Repeat steps 2-6 to set up another dropper of yeast glucose solution. Put that dropper
in the other water bath.
8. Allow the yeast-glucose solution to equilibrate (reach the same temperature) in the
water bath for 3-4 minutes.
9. Count the number of bubbles that rise from the tip of the dropper each minute for 10
minutes. Watch carefully—it is easy to miss the small bubbles!
10. Count the number of bubbles per minute for ten minutes. Record the data on Table I:
Influence of Temperature on Yeast Respiration (see Student Work Sheet)
Extension
Working with a partner design an experiment, using this basic procedure, to investigate some
aspect of respiration. Your options might include but are not limited to: different sugars,
temperatures, pH, concentration, and types of yeast. Once you have decided on a topic to
investigate please check with me before writing your procedure. Once you have written your
procedure you will need to check with me about materials.
Student Worksheet
Name: ___________________________________________________ Date: ______________
Burping Yeast
IMPORTANT: Read the background and procedure then do the pre-lab questions before
performing the experiment.
Prelab Questions:
1. Why do cells carry on cellular respiration?
2. How will the rate of respiration be measured?
3. Write a hypothesis about the effect of temperature on cellular respiration.
Observations and Results:
Table I Influence of Temperature on Yeast Respiration
Number of Bubbles
TIME (MINUTES)
1
2
3
4
5
6
7
8
9
10
TOTALS
30-40C
5-10C
Student Worksheet
Additional Observations:
Post-Lab Analysis:
1. Why was counting the number of bubbles an appropriate way to measure the rate of cellular
respiration?
2. What did the results indicate about the effect of temperature on the rate of cellular respiration?
3. Why did the temperature affect the rate of respiration?
Discussion:
Write a paragraph describing what you learned in this lab. This paragraph should include the
purpose of the lab, a summary of the results and significance of the results. Some of the
questions above will get you started.