The primary composition of a cell membrane consists of a phospholipid bilayer, proteins, cholesterol, and carbohydrates. The phospholipid bilayer forms the fundamental structure, providing a semi-permeable barrier that separates the cell's interior from its external environment. Embedded proteins serve various functions, including transport, signaling, and structural support. Cholesterol provides stability and fluidity to the membrane, while carbohydrates attached to proteins and lipids play a role in cell recognition and communication. This composition is critical for maintaining cellular homeostasis and functionality.