Fermentation vs Aerobic Respiration — NEET Biology
📚 Practice ConceptNow let us compare fermentation and aerobic respiration: • Fermentation accounts for only a partial breakdown of glucose whereas in aerobic respiration it is completely degraded to CO2 and H2O. • In fermentation there is a net gain of only two molecules of ATP for each molecule of glucose degraded to pyruvate and whereas many more molecules of ATP are generated under aerobic conditions. • FADH2 is oxidised to NAD+ rather slowly in fermentation, however the reaction is very vigorous in case of aerobic respiration.
Which of the following statements are correct regarding the comparison between fermentation and aerobic respiration? S1: Fermentation results in the complete degradation of glucose to CO₂ and H₂O, releasing a large amount of energy. S2: The low energy yield in fermentation is primarily due to the partial breakdown of glucose, where less than seven percent of the energy is released. S3: The oxidation of NADH to NAD⁺ occurs at a much slower rate in fermentation compared to aerobic respiration. S4: Both fermentation and aerobic respiration involve the trapping of energy as high-energy bonds of ATP through substrate-level phosphorylation only. S5: Oxygen acts as the final hydrogen acceptor in fermentation, driving the reoxidation of reducing equivalents.
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Correct answer: B — S2 and S3 are correct.
The core concept here is the difference in energy yield and process characteristics between fermentation and aerobic respiration. S1 is incorrect. Fermentation accounts for only a partial breakdown of glucose, not complete degradation to CO₂ and H₂O, which results in a low energy yield. Aerobic respiration results in complete degradation. S2 is correct. According to NCERT, "In fermentation... not much energy is released; less than seven per cent of the energy in glucose is released and not all of it is trapped as high energy bonds of ATP." This is due to incomplete oxidation. S3 is correct. NCERT states, "NADH is oxidised to NAD+ rather slowly in fermentation, however the reaction is very vigorous in case of aerobic respiration." S4 is incorrect. While substrate-level phosphorylation occurs in both (glycolysis part), aerobic respiration also involves oxidative phosphorylation, which is responsible for the majority of ATP synthesis. Fermentation only yields ATP via substrate-level phosphorylation during glycolysis. S5 is incorrect. Fermentation occurs under anaerobic conditions; oxygen is not involved. Oxygen acts as the final hydrogen acceptor in aerobic respiration. Fermentation yields less energy due to incomplete glucose oxidation, resulting in slower NADH reoxidation and only substrate-level phosphorylation.
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