Yeast is used for a number of commercial applications including alcohol fermentation. During fermentation, yeast is kept in anaerobic conditions. However, to increase yeast numbers (increase biomass), it is grown in aerobic conditions. Which of the following statements explains these different growing conditions? 1. Under anaerobic conditions, yeast converts pyruvate to acetyl CoA. 2. Under anaerobic conditions, yeast converts pyruvate into ethanol and carbon dioxide. 3. Under aerobic conditions, acetyl CoA enters the citric acid cycle in yeast. 4. Under aerobic conditions, yeast converts pyruvate into lactic acid.
A
1 and 3
B
1 and 4
C
2 and 3
D
2 and 4