Energy-rich organic compounds, such as fats, oils, and waxes, are called ______.

• A. Lipids
• B. Carbohydrates
• C. Proteins
• D. Nucleic Acids

Answer: (A)

Energy-rich organic compounds such as fats, oils, and waxes are lipids. Lipids are a diverse, mainly nonpolar group that includes triglycerides, phospholipids, waxes, and sterols. Their long hydrocarbon chains are highly reduced, so when they are oxidized they yield a large amount of energy—about 9 kcal per gram—making them ideal for long-term energy storage in adipose tissue. Beyond storage, lipids also have important roles: phospholipids are key components of cell membranes, waxes provide waterproofing, and other lipids contribute to membrane structure and signaling. Carbohydrates store energy more quickly and are more water-soluble but have a lower energy density (about 4 kcal per gram). Proteins are primarily used for enzymes, structures, and signaling, while nucleic acids store genetic information rather than energy.