8 Chapter 8 – Respiration

Respiration by Yeast


During respiration, undergo metabolic processes to obtain energy from the breakdown of sugars. However, yeast can only metabolize certain types of sugars. In order for yeast to utilize a particular sugar as a food source, it needs to have specific transport mechanisms to bring the sugar molecules into its cells. Additionally, the yeast must possess the necessary enzymes capable of breaking down the chemical bonds in the sugar molecules in a way that can be used for energy production.

Among the various sugars, is an essential source of energy for all living organisms, including yeast. Yeast can metabolize glucose through two different pathways: aerobic respiration and anaerobic fermentation. In , yeast utilize oxygen to break down glucose molecules completely, resulting in the production of carbon dioxide (CO2) and water (H2O) as byproducts. This process is highly efficient and yields a larger amount of energy in the form of ATP (adenosine triphosphate).

On the other hand, yeast can also carry out in the absence of oxygen. This process, known as fermentation, allows yeast to partially break down glucose molecules, resulting in the production of ethanol (alcohol) and carbon dioxide as byproducts. Although fermentation provides yeast with energy, it is less efficient compared to aerobic respiration.

In this lab, the objective is to investigate the ability of yeast to metabolize different sugars and observe . The four sugars being tested are glucose, , , and . The experiment involves using a CO2 Gas Sensor to measure the production of carbon dioxide by yeast as they respire using these sugars. The production of carbon dioxide indicates the metabolic activity of the yeast and provides insight into their ability to utilize the tested sugars as a food source.

By observing the rate and amount of carbon dioxide produced by the yeast when exposed to each sugar, it is possible to determine which sugars can be effectively metabolized by the yeast. This information helps in understanding the metabolic preferences and capabilities of yeast in utilizing different sugars for energy production.


Key Terms

  • Aerobic
  • Respiration rate
  • Sucrose
  • Anaerobic
  • Glucose
  • Fructose
  • Lactose



  • Use a C02 Gas Sensor to measure concentrations of carbon dioxide.
  • Determine the rate of respiration by yeast while using different sugars.
  • Determine which sugars can be used as a food source by yeast.



  • Vernier LabQuest 2 device
  • Water bath @ 38-40 °C
  • Vernier C02 Gas Sensor (2)
  • Test tube rack
  • Yeast Suspension*
  • Deionized water
  • 10x100mm test tubes (5)
  • 5% Glucose, Sucrose, Lactose, and Fructose sugar solutions
  • Disposable pipettes OR p-1000 Micropipettes with tips
  • 250ml respiration chamber or Erlenmeyer flask (5)

*Stock solution of yeast: 7g of yeast (1 packet) in 100 mL water prepared fresh for the class, placed in 38-40 °C water bath for 10 minutes.



1. What is the purpose of investigating the ability of yeast to metabolize different sugars in the lab?
2. How does yeast obtain energy from the breakdown of sugars during respiration?
3. What are the specific requirements for yeast to utilize a particular sugar as a food source?
4. Which sugar is considered an essential source of energy for all living organisms, including yeast?
5. What are the two pathways through which yeast can metabolize glucose?
6. Describe the byproducts produced during aerobic respiration of glucose by yeast.
7. What is the difference between aerobic respiration and anaerobic fermentation in yeast?
8. How does the efficiency of energy production differ between aerobic respiration and anaerobic fermentation in yeast?
9. What is the role of the CO2 Gas Sensor in the lab experiment?
10. How can observing the rate and amount of carbon dioxide produced by yeast when exposed to different sugars help determine their metabolic preferences and capabilities?




  1. Prepare a water bath for the yeast. A water bath is simply a large reservoir of water at a certain temperature. This ensures that the yeast will remain at a constant and controlled temperature. Make sure the digital water bath has several inches of water in the basin. Turn the water bath on and set the temperature at 38-40°C. Monitor the temperature of the water bath during the experiment.
  2. Connect the C02 Gas Sensor to the LabQuest 2 device: Insert the plug into the CHI port at the left side of the device. Set the sensor switch to low (0 – 10,000 ppm) setting. Turn on the LabQuest 2 by pressing the button at the top left of the device.
  3. To clear any unwanted data from the device before beginning the experiment, tap ‘File’, then select ‘New’ from the drop down menu. When prompted, tap ‘Discard’.
  4. Obtain five test tubes and label them G, S, F, L, and W.
  5. Obtain the four sugar solutions: glucose, sucrose, fructose, and lactose:
    1. Place 3 mL of the glucose solution in test tube G.
    2. Place 3 mL of the sucrose solution in test tube S.
    3. Place 3 mL of the fructose solution in test tube F.
    4. Place 3 mL of the lactose solution in test tube L.
    5. Place 3 mL of deionized water in test tube W.
  6. Obtain 15 mL of the yeast suspension. Gently swirl the yeast suspension to mix the yeast that settles to the bottom.
  7. Put 2 mL of the yeast suspension into the test tube labeled G (glucose). Gently swirl the test tube to mix the yeast into the solution.
  8. Set the test tube into the water bath and incubate for 10 minutes.
  9. When incubation is finished, use a pipet to place 3 mL of the solution from test tube G into the 250 mL respiration chamber or flask. Note the temperature of the water bath and record as the actual temperature in Table 1.
  10. Quickly place the shaft of the C02 Gas Sensor in the opening of the respiration chamber or flask. Gently twist the stopper on the shaft of the C02 Gas Sensor into the chamber opening. Do not twist the shaft of the C02 Gas Sensor or it could be damaged.
  11. Begin measuring the carbon dioxide concentration by tapping the green arrow ( at the bottom left of the screen. Collect data for 4 minutes (240 seconds), then press the red square to stop data collection. Pressing the arrow button on the right of the device will also start and stop data collection.
  12. A graph of C02 production over time will be displayed. Move your data to a stored run. To do this, tap on the filing cabinet icon at the top right of the screen.
  13. When data collection has finished, remove the C02 Gas Sensor from the respiration chamber. Use a notebook or notepad to fan air across the openings in the probe shaft of the C02 Gas Sensor for 1 minute.
  14. Repeat Steps 7 – 13 for the other four test tubes. Each run will be graphed a different color with a different shape for the data points (square, triangle, circle). It is a good idea to write down which graph represents which sugar.
  15. When data for all five tubes has been collected and stored, tap the screen next to the filing cabinet icon where it says ‘Run’. Select ‘All Runs’. The graphs for each sugar tested will be displayed.
  16. Determine the rate of respiration:
    1. Tap ‘Analyze’ from the top of the screen.
    2. Select ‘Curve Fit’ from the drop-down menu. Select the square for the first sugar tested.
    3. Tap the arrow next to ‘Choose Fit’ and select ‘Linear’. The formula for a best fit line will appear (y = mx + b).
    4. RECORD THE SLOPE OF THE LINE (m) AS THE RATE OF RESPIRATION IN TABLE 1. The rate of respiration given by m on the graph is in ppm/s. This should be converted to ppm/min for Table 1.
    5. Tap OK at the bottom right. This displays the best fit line on the graph.
    6. Determine the slope of the line (m) for each of the sugars by repeating steps 1 through 5, selecting the next square for the next sugar tested.
    7. To save and name your file, press “file” (top menu bar), then “save” (drop-down menu)
      • Name (Bench #) and save your file
    8. Go back to “file” and tap “export” in the drop-down menu.
      • Insert your USB (if LabQuest2 does not register the USB, ensure the USB is inserted properly)
    9. Highlight your named file and continue.
    10. It is now safe to remove the USB once exporting is complete.
    11. Upload your file to a device and make sure the entire group has a copy. You can use this file for data manipulation.
    12. Upload the data into the Respiration discussion board on Canvas.
  1. Once the data has been recorded and emailed, shut down the LabQuest 2:
    1. Clear the data by tapping ‘File’ and selecting ‘New’. Tap ‘Discard’ when prompted.
    2. Press the button on the device with the house icon.
    3. Select (System’, then ‘Shut Down’.
    4. Tap ‘OK’ when prompted.
  2. Return sensors and LabQuest 2 to the cart. Wash all glassware.
Table 1
Sugar Tested Temperature (°C) Respiration Rate (ppm/min)
Water (control)
Table 2: Class Averages (Optional)
Sugar Tested Respiration Rate (ppm/min)




  1. (Optional) When all other groups have posted their results on the board, calculate the average rate of respiration for each solution tested. Record the average rate values in Table 2.
  2. Make a bar graph of rate of respiration vs. sugar type. The rate values should be plotted on the y-axis, and the sugar type on the x-axis. Use the rate values from Table 1.
  3. Considering the results of this experiment, do yeast equally utilize all sugars? Explain.
  4. Hypothesize why some sugars were not metabolized while other sugars were.
  5. Why do you need to incubate the yeast before you start collecting data?
  6. Yeast live in many different environments. Make a list of some locations where yeast might naturally grow. Estimate the possible food sources at each of these locations.

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Biology I Cellular Processes Laboratory Manual by The authors & Hillsborough Community College is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License, except where otherwise noted.

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