The plasma membrane is composed of which molecular classes?

• A. Lipids, Proteins, and Carbohydrates
• B. Nucleic acids only
• C. Inorganic minerals only
• D. Water and salts only

Answer: (A)

Membranes are built from three main molecular classes: lipids form the bilayer that provides the structural foundation and barrier; proteins are embedded in or attached to that bilayer to control transport, signaling, and enzymatic activities; and carbohydrates decorate the outer surface as glycolipids and glycoproteins, contributing to cell recognition and protection.

Think of the phospholipid bilayer as the flexible matrix that creates the barrier, while proteins act as doors, gates, and receivers, and carbohydrates extend outward to communicate with other cells. Nucleic acids are not components of the membrane itself; they stay in the nucleus or cytoplasm for genetic information. Inorganic minerals and water/salts are not primary building blocks of the membrane, though water is present and minerals/salts are dissolved in the surrounding fluids.

So the plasma membrane is composed of lipids, proteins, and carbohydrates.