During cellular respiration in eukaryotes, which stage yields the most ATP overall?

During cellular respiration in eukaryotes, which stage yields the most ATP overall?

• A. Oxidative phosphorylation (electron transport chain) yields the most ATP.
• B. Glycolysis yields the most ATP.
• C. Citric acid cycle yields the most ATP.
• D. Fermentation yields the most ATP.

Answer: (A)

In aerobic cellular respiration, the stage that makes the most ATP is oxidative phosphorylation through the electron transport chain. Here’s why: NADH and FADH2 ferry high-energy electrons into the chain located in the inner mitochondrial membrane. As electrons pass along the chain, their energy pumps protons across the membrane, creating a big proton gradient. ATP synthase then uses that gradient like a turbine, converting ADP into ATP as protons flow back across the membrane. This process yields the vast majority of ATP from glucose—much more than glycolysis or the citric acid cycle can produce on their own. In total, you get around 26–28 ATP from oxidative phosphorylation per glucose, and when you add the small amounts made directly by glycolysis and the citric acid cycle, the overall yield is about 30–32 ATP per glucose under typical eukaryotic aerobic conditions. Fermentation, by comparison, can only generate about 2 ATP per glucose because it relies solely on glycolysis in the absence of oxygen.

In aerobic cellular respiration, the stage that makes the most ATP is oxidative phosphorylation through the electron transport chain. Here’s why: NADH and FADH2 ferry high-energy electrons into the chain located in the inner mitochondrial membrane. As electrons pass along the chain, their energy pumps protons across the membrane, creating a big proton gradient. ATP synthase then uses that gradient like a turbine, converting ADP into ATP as protons flow back across the membrane. This process yields the vast majority of ATP from glucose—much more than glycolysis or the citric acid cycle can produce on their own. In total, you get around 26–28 ATP from oxidative phosphorylation per glucose, and when you add the small amounts made directly by glycolysis and the citric acid cycle, the overall yield is about 30–32 ATP per glucose under typical eukaryotic aerobic conditions. Fermentation, by comparison, can only generate about 2 ATP per glucose because it relies solely on glycolysis in the absence of oxygen.