[Campbell Biology P.230] Refer to Figure 9.17 and the accompanying text. Which statement cor... | Practice Question

Refer to Figure 9.17 and the accompanying text. Which statement correctly describes the metabolic fate of pyruvate in a facultative anaerobe?

  • A: In the presence of oxygen, pyruvate is directly converted into ethanol or lactate in the cytosol.
  • B: When oxygen is present, pyruvate is transported into the mitochondrion and converted to acetyl CoA, leading to the citric acid cycle.
  • C: Under anaerobic conditions, pyruvate is fully oxidized to CO2 and H2O, yielding a large amount of ATP.
  • D: Facultative anaerobes only perform fermentation, regardless of oxygen availability.

Explanation

Figure 9.17 and the text explain that pyruvate represents a metabolic 'fork'. In facultative anaerobes like yeast , when O2 is present, pyruvate enters the mitochondrion, is converted to acetyl CoA, and proceeds through the citric acid cycle as part of aerobic cellular respiration. When O2 is absent, it undergoes fermentation.