Compare the amount of gas produced in tube 4 to that of tube 3. Galactose is an isomer of glucose. Are the yeast enzymes able to metabolize galactose as they do glucose? Considering enzyme specificity, explain these results.

 Alcohol Fermentation

1. During this experiment, gas pressure was measured. By what process was the gas produced? Which gas was it?

2. Yeast was added to all the tubes, but not all of them produced the gas. What had to be present in order for the gas to be made?

3. This experiment was run at approximately 45C. When performed at room temperature (24C), little if any gas would have been produced within the 15–minute sampling time. Why? (Hint: Refer back to Lab 9 on Enzymes.)

4. What was the purpose of layering the oil on top of the solutions in all 6 tubes?

5. Considering the contents of tube 1, explain why it is the negative control for this experiment.

6. Study the line on the graph for tube 2. Note that it increased steadily. However, at some point it will level off. Offer an explanation as to why

7. Compare the amount of gas produced in tube 3 to that of tube 2. How does the concentration
of glucose affect the rate of fermentation?

8. Compare the amount of gas produced in tube 4 to that of tube 3. Galactose is an isomer of glucose. Are the yeast enzymes able to metabolize galactose as they do glucose? Considering enzyme specificity, explain these results.

9. NaF is the enzyme inhibitor in tube 5.

a. Did any fermentation occur in test tube 5?
b. Because NaF blocks the last enzyme of glycolysis, what end product of glycolysis is not produced when NaF is present?
c. Why does the lack of this end product stop fermentation?
d. Does NaF inhibit enzymes located in the cytoplasm or the mitochondria?

10. KCN is the enzyme inhibitor in tube 6.

a. Since KCN is an enzyme inhibitor, why was there gas production in this tube?
b. Does KCN inhibit enzymes located in the cytoplasm or the mitochondria?
c. Compare the slopes for tubes 3 and 6. Explain why they are very similar.

11. Fermentation does not produce any ATP. So, what is its value to the yeast?

12. Why is this type of fermentation called alcohol fermentation? (Be specific.)

a. The initial substrate,_, has _ carbons.
b. The final product of alcohol fermentation is two molecules of _ with a total
of _ carbons.
c. What happened to the “missing” carbons?

14. Give 2 potential sources of error in this experiment.