Question

1. Why do yeasts perform alcohol fermentation?

2. What is the chemical reaction for fermentation?

3. Which are the reactants in this reaction? Which are the products?

4. What is the gas that accumulates in the bag, causing it to inflate? In addition to this gas,

what is another product of this process? Can you think of one example when either of these

products is useful during cooking/baking?

5. How does inflation of the bag correlate with the amount of carbon dioxide produced? (If

the bag is very inflated, what does that tell you about the amount of carbon dioxide

produced? What if it is remains very deflated?)

6. How does the amount of carbon dioxide correlate with the rate of sugar consumed by yeast?

7. Is alcohol fermentation an efficient process to produce ATP? How many ATP molecules are

produced per glucose molecule by aerobic respiration in eukaryotic cells (yeasts)? How

many ATP molecules are produced per glucose molecule by alcohol fermentation?

Answer 1

The yeast breaks down glucose forming; 2 pyruvate molecules by glycolysis. Followed by conversion of the 2 pyruvate molecules to ethanol; this second part is known as fermentation. The yeasts perform alcoholic fermentation as they have all the enzymes needed in the pathway of alcoholic fermentation, i.e. the glycolytic enzymes and the enzymes to change pyruvate to ethanol.