Algonquin College Health Program Assessment (AC-HPAT) Practice Exam

What is the primary composition of the cell membrane?

1. Proteins

2. Phospholipids

3. Cholesterol

4. Carbohydrates

The correct answer is: Phospholipids

The primary composition of the cell membrane is phospholipids. This is because phospholipids form the fundamental structure of the membrane, creating a bilayer that acts as a barrier between the inside of the cell and the external environment. The hydrophilic (water-attracting) heads of phospholipids face outward toward the watery environments, while the hydrophobic (water-repelling) tails face inward, away from water. This unique arrangement allows the cell membrane to maintain its integrity and selectively control the passage of substances in and out of the cell. In addition to phospholipids, the cell membrane contains proteins, cholesterol, and carbohydrates, but these components mainly serve supportive and regulatory functions. Proteins are involved in signaling, transport, and structural roles within the membrane. Cholesterol helps to maintain membrane fluidity and stability, especially in varying temperatures. Carbohydrates are typically involved in cell recognition and communication, but they do not form the structural foundation of the membrane. Therefore, while all these components are crucial for the membrane's function, phospholipids are the primary building blocks that define its structure.