Which statement is true about ATP yield in respiration?

Which statement is true about ATP yield in respiration?

• A. Aerobic respiration yields more ATP per glucose than anaerobic respiration
• B. Anaerobic respiration yields more ATP per glucose than aerobic respiration
• C. Both yield the same amount of ATP per glucose
• D. Aerobic respiration yields no ATP

Answer: (A)

In respiration, energy yield from glucose depends on whether oxygen is present. With oxygen, glucose is fully oxidized in mitochondria through glycolysis, the citric acid cycle, and the electron transport chain. The electron transport chain pumps protons to create a gradient, and ATP synthase uses that gradient to make most of the ATP, giving about 30–32 ATP per glucose. Without oxygen, the process can’t complete electron transport, so cells rely on glycolysis alone (and often fermentation to recycle NAD+), which yields only about 2 ATP per glucose. So aerobic respiration produces far more ATP per glucose than anaerobic respiration. The idea that both yield the same amount or that aerobic yields no ATP isn’t accurate because glycolysis already provides some ATP, and mitochondria provide the large additional amount when oxygen is available.

In respiration, energy yield from glucose depends on whether oxygen is present. With oxygen, glucose is fully oxidized in mitochondria through glycolysis, the citric acid cycle, and the electron transport chain. The electron transport chain pumps protons to create a gradient, and ATP synthase uses that gradient to make most of the ATP, giving about 30–32 ATP per glucose. Without oxygen, the process can’t complete electron transport, so cells rely on glycolysis alone (and often fermentation to recycle NAD+), which yields only about 2 ATP per glucose. So aerobic respiration produces far more ATP per glucose than anaerobic respiration. The idea that both yield the same amount or that aerobic yields no ATP isn’t accurate because glycolysis already provides some ATP, and mitochondria provide the large additional amount when oxygen is available.