Which of the following substances can be metabolized anaerobically?

• A. Glycerol
• B. Glucose
• C. Amino acids
• D. Free fatty acids

Answer: (B)

When oxygen is scarce, the body relies on anaerobic glycolysis to make ATP. This process uses glucose, converting it to pyruvate and then to lactate, while regenerating NAD+. The net energy yield is small but fast, which is why glucose is the primary fuel for rapid, anaerobic energy production during high-intensity efforts.

Glycerol can enter glycolysis later in the pathway, but it isn’t the main substrate for rapid anaerobic energy and its flux is slower. Free fatty acids require beta-oxidation and subsequent mitochondrial oxidative processes, which need oxygen. Amino acids can feed into energy pathways, but their use is not a straightforward, efficient anaerobic route and is more context-dependent.

Therefore, glucose is the substrate that can be metabolized anaerobically to support quick ATP production without oxygen.