- A Generally during the light reactions of photosynthesis in chloroplasts according to standard texts in general clinical practice
- B Directly during a reaction step of glycolysis or the Krebs cycle, without involving the electron transport chain
- C Mainly within the mitochondrial inner membrane through ATP synthase activity under most conditions studied
- D Mostly after oxygen acts as the final electron acceptor at the chain's end in most observed cases under typical physiological conditions
Correct answer: B. Directly during a reaction step of glycolysis or the Krebs cycle, without involving the electron transport chain
Explanation: Substrate-level phosphorylation generates ATP directly from a high-energy intermediate during specific glycolysis and Krebs cycle reactions, distinct from the chemiosmotic ATP synthesis of oxidative phosphorylation.
Concept context
Glycolysis, the Krebs cycle, the electron transport chain, fermentation, and the respiratory quotient. The cellular energy-release counterpart to photosynthesis.