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Experimenting with Yeast Metabolism

Students will use multiple technologies to gain an understanding of yeast metabolism.

Objectives

Use a CO2 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.

    Procedure

    Adapted from Biology with Computers by David Masterman and Kelly Redding available at: http://www.vernier.com/cmat/bwc.html.

    1. Prepare a water bath for the yeast. A water bath is simply a large beaker of water at a certain temperature. This ensures that the yeast will remain at a constant and controlled temperature. To prepare the water bath, obtain some warm and cool water from your teacher. Combine the warm and cool water into the 600-mL beaker until it reaches 38- 40 degrees celsius. The beaker should be filled with about 300-400 mL water. Leave the thermometer in the water bath during the course of the experiment to monitor the temperature of the water bath.

    2. Obtain five test tubes and label them G, S, F, L, and W.

    3. Obtain the four sugar solutions: glucose, sucrose, fructose, and lactose.
      • Place 2 mL of the glucose solution in test tube G.
      • Place 2 mL of the sucrose solution in test tube S.
      • Place 2 mL of the fructose solution in test tube F.
      • Place 2 mL of the lactose solution in test tube L.
      • Place 2 mL of distilled water in test tube W.

    4. Obtain the yeast suspension. Gently swirl the yeast suspension to mix the yeast that settles to the bottom. Put 2 mL of yeast into each of the five test tubes. Gently swirl each test tube to mix the yeast into the solution.

    5. Set the five test tubes into the water bath.

    6. Incubate the test tubes for 10 minutes in the water bath. Keep the temperature of the water bath constant. If you need to add more hot or cold water, first remove as much water as you will add, or the beaker may overflow. Use a beral pipet to remove excess water. While the test tubes are incubating, proceed to Step 7.

    7. Prepare the computer for data collection by opening the file in the Experiment 12 folder of Biology with Computers. The vertical axis has Carbon Dioxide concentration scaled from 0 to 5000 ppm. The horizontal axis has time scaled from 0 to 4 minutes. The data rate is set to 4 samples/minute.

    8. When incubation is finished, use a beral pipet to place 1 mL of the solution in test tube G into the 250-mL respiration chamber. Note the temperature of the water bath and record as the actual temperature in Table 1.

    9. Quickly place the shaft of the CO2 Gas Sensor in the opening of the respiration chamber. Gently twist the stopper on the shaft of the CO2 Gas Sensor into the chamber opening. Do not twist the shaft of the CO2 Gas Sensor or you may damage it.

    10. Begin measuring carbon dioxide concentration by clicking collect. Data will be collected for 4 minutes.

    11. When data collection has finished, remove the CO2 Gas Sensor from the respiration chamber. Fill the respiration chamber with water and then empty it. Make sure that all yeast have been removed. Thoroughly dry the inside of the chamber with a paper towel.

    12. Determine the rate of respiration:
      • Move the mouse pointer to the point where the data values begin to increase. Hold down the left mouse button. Drag the pointer to the end of the data and release the mouse button.
      • Click on the Regression button to perform a linear regression. A floating box will appear with the formula for a best fit line.
      • Record the slope of the line, m, as the rate of respiration in Table 1.
      • Close the linear regression floating box.
      • Share your data with the class by recording the sugar type and respiration rate on the board.

    13. Move your data to a stored run. To do this, choose Store Latest Run from the Data menu.

    14. Use a notebook or notepad to fan air across the openings in the probe shaft of the CO2 Gas Sensor for 1 minute.

    15. Repeat Steps 8-14 for the other four test tubes.
  • Sunshine State Standards

    • SC.H.1.4
    • SC.F.1.4
    • MA.8.S.3.1
    • MA.912.A.3.11

    NETS Profiles for Technology Literate Students

    • Select and apply technology tools for research, information analysis, problem-solving, and decision-making in content learning. (4, 5)
    • Collaborate with peers, experts, and others to contribute to a content-related knowledge base by using technology to compile, synthesize, produce, and disseminate information, models, and other creative works. (4, 5, 6)

    Materials

    • Power Macintosh or Windows PC
    • Vernier Computer Interface- LabPro
    • Logger Pro
    • Vernier CO2 Gas Sensor
    • 250-mL respiration chamber
    • 5% glucose, sucrose, lactose, and fructose sugar solution
    • 600-mL beaker (for water bath)
    • Beral pipettes
    • Hot and cold water
    • Thermometer
    • Four 10 x 100mm test tube
    • Yeast suspension Graphical Analysis (optional)

    Alternatives/Extensions

    • Students can further their knowledge of respiration by using an O2 Sensor or testing artificial sweeteners.


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