Which class of molecules includes fats, phospholipids, and steroids?

• A. Carbohydrate
• B. Lipid
• C. Protein
• D. Nucleic Acid

Answer: (B)

Lipids are a broad set of molecules that are largely nonpolar and do not share a single repeating monomer, unlike sugars, amino acids, or nucleotides. Fats, phospholipids, and steroids all fall into this group. Fats store energy efficiently and consist of a glycerol backbone with three fatty acids. Phospholipids have two fatty acids and a phosphate-containing head, making them amphipathic and ideal for forming cell membranes. Steroids share a four-ring structure and function in signaling and hormone activities. Carbohydrates, proteins, and nucleic acids are built from repeating monomer units (sugars, amino acids, nucleotides), so they don’t include fats, phospholipids, or steroids.