Glycogen is best described as

• A. A protein
• B. A lipid
• C. A carbohydrate used for energy storage in animals
• D. A nucleic acid

Answer: (C)

Glycogen is a carbohydrate, specifically a glucose polymer that serves as the rapid energy reserve in animals. Its highly branched structure lets enzymes quickly add or remove glucose units, so energy can be released fast when muscles need to work or blood sugar needs to be steadied. It’s stored mainly in the liver and skeletal muscles for quick access. It’s not a protein, since it isn’t made from amino acids and doesn’t function as an enzyme or structural protein. It isn’t a lipid—which are hydrophobic molecules used for long-term energy storage in a different form—nor a nucleic acid, which are polymers of nucleotides that store and transmit genetic information. So glycogen best fits as a carbohydrate used for energy storage in animals.