A biomolecule consisting of a chain of hydrocarbons is what type of compound?

• A. Vitamin
• B. Protein
• C. Carbohydrate
• D. Lipid

Answer: (D)

Lipids are defined by long, nonpolar carbon-hydrogen chains. This hydrocarbon-rich structure makes them hydrophobic and not soluble in water, which explains their roles in energy storage (as fats and oils) and in forming cell membranes (phospholipids with fatty acid tails). Some lipids also include hydrocarbon ring systems, like steroids. In contrast, vitamins are small organic compounds essential in tiny amounts, carbohydrates are built from sugar units with many polar groups and are water-loving, and proteins are polymers of amino acids with a wide range of side chains. So the description of a biomolecule consisting of a chain of hydrocarbons points to a lipid.