Answer: Four.
- A Two
- B Six
- C Eight
- D Four
Correct answer: D. Four
Explanation: Substrate-level phosphorylation yields 2 ATP in glycolysis and 2 in the Krebs cycle - four in all; the rest come from the ETC.
Aerobic respiration unfolds in three locations: glycolysis in the cytoplasm yields a small amount of ATP directly, the Krebs cycle in the mitochondrial matrix harvests electron carriers (NADH, FADH2), and the electron transport chain in the inner mitochondrial membrane uses those carriers to generate the bulk of the ATP, with O2 needed only at this final stage.
Concept context
Glycolysis, the Krebs cycle, the electron transport chain, fermentation, and the respiratory quotient. The cellular energy-release counterpart to photosynthesis.