January, 2002, Biology Experiment:

Effect of Respiration
on Dissolved Oxygen
Concentrations

- Purpose
- Background Information
- Equipment
- Pre-Lab Preparation
- Software Set-up
- Experimental Procedure
- Data Analysis
- Conclusions and Extensions


(Photo published in Microbiol. Rev. 54: 381-431, 1990)

Saccharomyces cerevisiae, baker’s or brewer’s yeast.
Bud scars of six daughter cells are shown in blue.

Dissolved Oxygen Sensor (PS-2108)

Purpose:

Students will measure the concentration of dissolved oxygen in a dilute glucose solution, both before and after the addition of a small amount of yeast suspension. Students will predict how the presence of yeast will affect the amount of dissolved oxygen in solution.

Background Information:

During cellular respiration, organisms break down carbohydrates to release energy. Cellular respiration begins with glycolysis, where glucose is converted to pyruvic acid. Then, depending on whether oxygen is present, either anaerobic fermentation or aerobic cellular respiration will occur. The complete oxidation of glucose in aerobic cellular respiration is summarized by the following equation:

C6H12O6 + 6O2  -->  6H2O + 6CO2 + energy

In the absence of oxygen, yeast will respire anaerobically and produce ethanol and carbon dioxide. This is inefficient (ultimately the ethanol will kill the yeast), but fermentation enables the yeast to survive and grow where no oxygen is available. Aerobic cellular respiration produces far more ATP and is therefore more efficient. Yeast metabolism is determined in part by the temperature of the surrounding environment, so aerobic cellular respiration in yeast is particularly sensitive to temperature.

Hypothesize: What effect will yeast have on the concentration of dissolved oxygen in solution? How will temperature influence this effect? (Hint: consider how dry yeast becomes "activated".)

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Equipment:

For each lab group:

Additional equipment:

  • 1 package active dry yeast per class section
  • 1-L bottle and graduated cylinder for preparation of yeast suspension
  • Balance and weighing paper for measuring sugar

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Pre-Lab Preparation: Yeast Suspension

For best results, prepare a yeast suspension about 30 minutes before class: data can then be collected in a shorter period of time, and dissolved oxygen concentration changes in the water will begin to occur very soon after yeast is added to the beaker.
  • For a single class, activate the yeast by adding 150 mL of warm water (30° to 35°C) to 1 package (approximately 7 to 9 grams) of dry yeast and 1 gram of sucrose (sugar). Mix well to assure that the yeast is thoroughly wetted. In 5 -10 minutes foam and the "yeasty" aroma of the evolved gases will indicate that sugar metabolism has begun.

  • Alternative: If you plan to run this lab over the course of the day and in several classes, instead of making a new suspension for each class you can make a single, larger batch by adjusting the recipe accordingly. For example, for five classes begin with (150 mL x 5) = 750 mL of warm water and 5 packages of yeast. However, add only 1 gram of sucrose (sugar) to the initial mix; add 1 additional gram of sugar to the remaining suspension 10 - 15 minutes before each class begins. This will provide each class with a suspension that has approximately the same "activity" level but without a buildup of toxic levels of waste by the end of the day.

  • The suspension will be suitable for use for the remainder of the day without incubation as long as the temperature does not fall below 20°C. However, the suspension cannot be stored overnight; make a new batch for each day you run trials.

Software Setup:

  1. Click on one of the links below to download a pre-configured DataStudio file for this dissolved oxygen experiment, and then open the file.

    PASPORT users: Windows (.zip file) or Macintosh (.sit file)

    ScienceWorkshop 500 users: Windows (.zip file) or Macintosh (.sit file)

    When the file is opened, you should see a graph display of Oxygen Concentration versus Time, as well as digits displays of oxygen concentration and temperature.

  2. Connect each sensor, Dissolved Oxygen and Temperature, to an Xplorer or USB link (PASPORT users), or plug the sensors into the 500 interface (ScienceWorkshop 500 users). If you are using the ScienceWorkshop 500 interface, be sure the sensors are associated correctly in the Experiment Setup window when you open the DataStudio file.

  3. Resize and arrange the displays as needed so that you can see them all.

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Experimental Procedure:

Sensor calibration:

  1. PASPORT users: Refer to the "Setup and Calibration" instructions and the Calibration Table on the Quick Start card for calibration procedures.

  2. ScienceWorkshop 500 interface users: Refer to the Dissolved Oxygen Sensor Instruction Manual and Experiment Guide, including Table 1 on page 28, for calibration procedures.

Data Recording:

  1. Measure 400 mL of room-temperature distilled water and pour it into the 1-L bottle. Close the lid tightly and shake vigorously (10 – 20 seconds) to oxygenate the water.

  2. Pour the oxygenated water into the 600-mL beaker and dissolve 5 grams of sugar into it.

  3. Put the Temperature Sensor and Dissolved Oxygen Sensor into the sugar solution and begin stirring gently.
  4. Click the Start button (  ) to begin collecting data. Continue stirring.

  5. After 30 seconds, add the 5-mL sample of activated yeast suspension to the beaker. Continue stirring and recording data.

  6. Record data until the dissolved oxygen level stabilizes (approximately 10 minutes), then click the Stop (  ) button.

Additional data runs: As time permits, additional data runs can be recorded using oxygenated water that is slightly colder or warmer than room temperature.

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Data Analysis:

  1. Examine the graph display to view your data, using the Scale to Fit button (  ) in the Graph toolbar to resize the axes.

  2. Determine the minimum and maximum values for the concentration of dissolved oxygen: click the Statistics button (  ) in the Graph toolbar and look for the minimum and maximum values to appear in the graph legend.

  3. Use the Slope tool (  ) to determine when during the data run the concentration of dissolved oxygen changed most quickly.

  4. If additional data runs were recorded using solutions at different temperatures, compare the Oxygen Concentration graphs over time for each run.

Conclusions and Extensions:

  1. What effect did the addition of the yeast suspension have on the amount of dissolved oxygen in the water? Describe the changes that were observed over time.

  2. What evidence do you have that the yeast cells were alive and respiring?

  3. What happens to the yeast cells when the dissolved oxygen concentration reaches a minimum? Is there any evidence the yeast cells are still alive?

  4. What effect did temperature have on the dissolved oxygen concentration over time?

  5. Design an experiment to investigate the effect of sugar concentration on respiration rate. How might the Oxygen Concentration graph be different?