Barley & Oat’s Brewing Backfire!
By Dr. Ingrid Waldron, John Coulter and Dr. Jennifer Doherty, Department of Biology, University of Pennsylvania, November, 2010[1]
Name: ______Date:______
Mr. Barley and Ms. Oat are opening a new beer brewing company, Barley & Oat’s Brews. Neither of them has brewed beer before, but they have an instruction manual and the supplies they need, including yeast and barley (which provides a source of sugar for the yeast to use as food). The only problem is that the beer that they have made does not have any alcohol in it! They can’t figure out why, so they have hired you to figure out why alcohol is not being produced.
Mr. Barley and Ms. Oat have given you some information that could be helpful to solve their problem. They found the figure below in the instruction manual for making beer. Ovals represent processes and rectangles represent some of the reactants and products.
1. Which process produces ethanol (the alcohol found in beer)?
2. Which molecule is needed for aerobic respiration but not for fermentation?
3. How many molecules of ATP are produced for each glucose molecule undergoing aerobic respiration (including glycolysis, Krebs cycle and electron transport chain)?
4. How many molecules of ATP are produced for each glucose molecule undergoing glycolysis followed by fermentation?
5. Why do yeast cells need ATP?
6. The yeast used to make beer can perform aerobic respiration or alcoholic fermentation. When O2 is available, yeast perform aerobic respiration, and when O2 is not available, yeast perform alcoholic fermentation. What is the advantage of aerobic respiration?
What is the advantage of fermentation?
With this background you are ready to interpret the evidence collected by Mr. Barley and Ms. Oat as they tried to brew beer. Mr. Barley carried out an experiment to test whether increasing the amount of sugar would increase the amount of alcohol produced. The figure shows the results of his experiment.
7. What was the independent variable Mr. Barley changed in the experiment?
What axis is this variable on?
8. What two dependent variables did Mr. Barley measure?
What axis are these variables on?
9. How did alcohol production change in response to higher sugar concentrations?
10. How did CO2 production change in response to higher sugar concentrations?
Ms. Oat measured the change in concentrations of O2, CO2 and ethanol while trying to brew her beer.
0 = beginning / 1.00 / 0.01 / 0
1 / 0.99 / 0.02 / 0
2 / 0.98 / 0.03 / 0
3 / 0.97 / 0.03 / 0
4 / 0.97 / 0.04 / 0
5 / 0.96 / 0.05 / 0
6 / 0.95 / 0.05 / 0
7 / 0.94 / 0.06 / 0
8 = end / 0.94 / 0.06 / 0
11. How did the amount of O2 in the brewing vat change over time?
12. How did the amount of CO2 in the brewing vat change over time?
13. How did the amount of ethanol in the brewing vat change over time?
Now you are ready to put together all the evidence and figure out why the beer produced by Barley and Oat’s Brews does not have any alcohol and what Mr. Barley and Ms. Oats should do to make real beer.
14. Was the yeast in the brewing vats of Barley and Oat’s Brews performing aerobic respiration or alcoholic fermentation? What evidence supports this conclusion?
15. What characteristic of the environment in the brewing vat determines whether the yeast perform aerobic respiration or alcoholic fermentation?
16. What do Mr. Barley and Ms. Oat need to do to make sure they have alcohol in their beer?
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[1] Teachers are encouraged to copy this student handout for classroom use. A Word file (which can be used to prepare a modified version if desired), teacher notes, comments, and links to additional activities are available at http://serendip.brynmawr.edu/exchange/bioactivities.