Which substrate is primarily used to produce energy in aerobic metabolism?

• A. Glucose
• B. Protein
• C. Nucleic acids
• D. Vitamins

Answer: (A)

Glucose is the main fuel used to generate energy in aerobic metabolism. It enters glycolysis in the cytosol, producing pyruvate, which is then converted to acetyl-CoA and feeds the citric acid cycle. The resulting NADH and FADH2 donate electrons to the electron transport chain, with oxygen as the final electron acceptor, driving ATP production. This pathway provides a reliable and rapid source of ATP under normal conditions, supporting tissues with high energy demands.

Proteins can supply energy when carbohydrates are scarce, but amino acids are not the typical primary source in aerobic conditions. Nucleic acids are not used for energy, and vitamins act as cofactors needed for metabolic reactions rather than direct energy substrates.