ATP Yield Calculations: Theory vs Reality — NEET Biology
📚 Practice ConceptIt is possible to make calculations of the net gain of ATP for every glucose molecule oxidised; but in reality this can remain only a theoretical exercise. These calculations can be made only on certain assumptions that:
Which of the following statements accurately reflects the assumptions made when determining the theoretical maximum ATP yield from one glucose molecule in aerobic respiration? S1. All intermediate products formed during the pathway are exclusively channeled towards the next step, without any diversion for anabolic processes. S2. The entire process of glucose oxidation, including glycolysis, Krebs cycle, and ETS, proceeds in a strictly sequential and orderly fashion. S3. NADH molecules generated in the cytoplasm during glycolysis are directly transferred into the mitochondrial matrix without any energy cost. S4. Only glucose is considered as the respiratory substrate, precluding the entry of other macromolecules at various intermediary points. S5. The efficiency of electron transport chain coupling to ATP synthase is absolute, resulting in precise ATP yields (e.g., 3 ATP per NADH, 2 ATP per FADH₂).
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Correct answer: D — S1, S2, S3, S4 and S5
The theoretical calculation of ATP yield in aerobic respiration is based on several key assumptions: S1. Correct. The assumption is that "None of the intermediates in the pathway are utilised to synthesise any other compound." S2. Correct. It is assumed that "There is a sequential, orderly pathway functioning, with one substrate forming the next and with glycolysis, TCA cycle and ETS pathway following one after another." S3. Correct. The calculation assumes that "The NADH synthesised in glycolysis is transferred into the mitochondria and undergoes oxidative phosphorylation." This implies direct and efficient transfer without any reduction in ATP yield. S4. Correct. A fundamental assumption is that "Only glucose is being respired – no other alternative substrates are entering in the pathway at any of the intermediary stages." S5. Correct. The fixed conversion rates of 3 ATP per NADH and 2 ATP per FADH₂ in the balance sheet implicitly assume absolute efficiency in the electron transport chain and ATP synthase coupling. Therefore, all statements S1, S2, S3, S4, and S5 accurately reflect assumptions made in the theoretical ATP yield calculation. Final Answer: The final answer is D.
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