Canadian Society for Medical Laboratory Science (CSMLS) Practice Exam

What is the primary component of the cell membrane?

1. Proteins

2. Lipids

3. Carbohydrates

4. Nucleic acids

The correct answer is: Lipids

The cell membrane is primarily composed of lipids, particularly phospholipids, which form a bilayer that serves as a barrier and provides structure to the membrane. This lipid bilayer is essential for maintaining the integrity of the cell, allowing it to protect its internal environment while controlling the movement of substances in and out of the cell. The unique arrangement of phospholipids in the bilayer allows for fluidity and flexibility, which are key characteristics of cell membranes. The hydrophilic (water-attracting) heads of the phospholipids face outward toward the aqueous environment, while the hydrophobic (water-repelling) tails face inward, creating a semi-permeable membrane. While proteins, carbohydrates, and nucleic acids play important roles in the functionality of the cell membrane—such as facilitating transport, communication, and recognition—they are not the primary structural components. Proteins embedded in the membrane can act as channels or receptors, carbohydrates often attach to proteins or lipids for cell recognition, and nucleic acids are not components of the membrane itself. Thus, the fundamental structure of the cell membrane is defined by its lipid composition, making lipids the correct answer.