Triglycerides are the major energy storage molecules in animals. Which lipid class best describes triglycerides?

• A. Phospholipids
• B. Waxes
• C. Steroids
• D. Triglycerides

Answer: (D)

Energy storage in animals is carried by a lipid designed for high energy density and compact packaging. Triglycerides have a glycerol backbone with three fatty acids attached by ester bonds, creating a triacylglycerol molecule. This structure makes them highly energy-rich and hydrophobic, so they dissolve little water and can be stored in adipose tissue as fat droplets. This storage role distinguishes them from other lipid types: phospholipids have a phosphate-containing head and two fatty acids and mainly form cell membranes; waxes are long-chain esters used for protection and waterproofing; steroids have a four-ring structure and are involved in signaling and other functions rather than energy storage. Thus, triglycerides describe the storage lipid class that best matches their purpose and composition.