Muscle cells serve as a reservoir for which of the following?

• A. Fatty acids
• B. Glucose
• C. Amino acids
• D. Lactate

Answer: (B)

Muscle cells store glucose primarily as glycogen, a glucose polymer that acts as a quick-release energy reserve for contraction. When exercise starts, glycogen is broken down to glucose-6-phosphate and funneled into glycolysis to produce ATP right in the muscle. Muscles can’t release free glucose into the bloodstream because they lack the enzyme needed to convert glucose-6-phosphate back to glucose, so this reservoir serves the muscle itself rather than maintaining blood glucose levels. While fatty acids are stored as intramuscular triglycerides and lactate is a metabolic byproduct, the main glucose-related reservoir in muscle is glycogen. Amino acids are mainly tied up in muscle proteins, not stored as a glucose reservoir.