How many ATP are produced from one glucose molecule during cellular respiration?

• A. About 36-38
• B. About 2-4
• C. About 10-12
• D. About 50

Answer: (A)

Under aerobic conditions, one glucose molecule released its energy through glycolysis, pyruvate oxidation, the Krebs cycle, and the electron transport chain. The total ATP yield is commonly estimated around 36–38 ATP per glucose because there’s variation in how efficiently the NADH produced in glycolysis is converted to ATP inside the mitochondria.

Breaking it down helps: glycolysis makes 2 ATP directly and produces 2 NADH. If those NADH are counted with a high efficiency, they contribute about 6 ATP. Pyruvate oxidation adds 2 NADH, contributing about 6 ATP. The Krebs cycle generates 6 NADH (about 18 ATP), 2 FADH2 (about 4 ATP), and 2 ATP equivalent from substrate-level phosphorylation (GTP). Adding those up with the glycolysis total gives about 38 ATP in the classic accounting.

In many cells, especially eukaryotes, the NADH from glycolysis must be shuttled into mitochondria, and the shuttle system affects how much ATP those NADH produce (roughly 2.5 ATP per NADH with some shuttles or about 1.5 ATP per NADH with others). That shifts the practical yield downward, commonly to about 30–32 ATP in human cells, or around 36–38 under less restrictive, ideal counting.

So the range of about 36–38 ATP per glucose is a widely used estimate for the total energy yield in aerobic respiration, recognizing that the exact number depends on the shuttle mechanism and organism.