What is the primary composition of the plasma membrane?

• A. Phospholipid bilayer with embedded proteins.
• B. Proteins only.
• C. Carbohydrate polymers.
• D. Nucleic acids.

Answer: (A)

The plasma membrane is built mainly from a phospholipid bilayer with embedded proteins. Phospholipids form two layers with hydrophilic heads facing the watery environment inside and outside the cell, and hydrophobic tails tucked between them, creating a flexible, semi-permeable barrier. Proteins interspersed in and across the bilayer provide channels, transport, receptors, and enzymes, giving the membrane its diverse functions. Carbohydrates attached to lipids and proteins (glycolipids and glycoproteins) sit on the surface and aid in cell recognition, but they’re not the primary structural component. Nucleic acids aren’t part of the membrane; they reside in the nucleus and other organelles.