Humber Admissions Practice Test

What component of the cell membrane is responsible for creating a barrier?

1. Proteins

2. Phospholipids

3. Cholesterol

4. Carbohydrates

The correct answer is: Phospholipids

The phospholipids play a crucial role in forming the cell membrane's barrier. They consist of hydrophilic (water-attracting) heads and hydrophobic (water-repelling) tails, which arrange themselves into a bilayer. This bilayer structure is fundamental to the membrane because it separates the internal environment of the cell from the external surroundings. The hydrophilic heads face outward toward the water inside and outside the cell, while the hydrophobic tails face inward, away from the water. This arrangement prevents water-soluble substances from easily passing through, thus maintaining the integrity of the cell and controlling the movement of materials across the membrane. The other components of the cell membrane, while important, do not primarily create the barrier. Proteins contribute to various functions, including transport and signaling, cholesterol helps to stabilize the membrane fluidity, and carbohydrates play a role in cell recognition and communication, but none of them establishes the fundamental barrier that phospholipids do.