AEMCA Practice Exam

What is the primary component of the cell membrane?

1. A phospholipid bi-layer made up of hydrophobic tails and hydrophilic heads

2. Composed only of cholesterol molecules

3. A rigid layer of cellulose

4. A single layer of proteins

The correct answer is: A phospholipid bi-layer made up of hydrophobic tails and hydrophilic heads

The primary component of the cell membrane is indeed a phospholipid bilayer, which consists of hydrophobic tails and hydrophilic heads. This structure is crucial for the functionality of the cell membrane. The hydrophobic tails face inward, away from water, while the hydrophilic heads face outward towards the aqueous environment both inside and outside the cell. This arrangement forms a semi-permeable barrier that controls the movement of substances in and out of the cell, thereby maintaining homeostasis. Additionally, the fluid nature of this bilayer allows for the mobility of proteins and lipids within the membrane, facilitating various functions such as signaling, transport, and cell recognition. This complex organization contrasts with other options that do not accurately reflect the structure of the cell membrane. Cholesterol molecules, while essential for membrane fluidity and stability, are not the primary component. Similarly, cellulose is found in plant cell walls, not in cell membranes, and a single layer of proteins does not provide the necessary structural integrity or functional versatility that the bilayer offers.