- A Mitochondrial electron transport chains are saturated with surplus oxygen
- B Oxygen supply is insufficient (anaerobic conditions/oxygen debt)
- C Glycogen stores are fully depleted after prolonged starvation
- D Cytoplasmic ATP concentration exceeds the cell's regulatory threshold
Correct answer: B. Oxygen supply is insufficient (anaerobic conditions/oxygen debt)
Explanation: Under oxygen debt (vigorous exercise), muscle cells convert pyruvate to lactic acid to regenerate NAD+ for glycolysis to continue, without needing O2.
Concept context
Glycolysis, the Krebs cycle, the electron transport chain, fermentation, and the respiratory quotient. The cellular energy-release counterpart to photosynthesis.