What is the primary role of cholesterol in the cell membrane?

• A. It acts as a channel protein for ion transport.
• B. It increases membrane fluidity at low temperatures and decreases fluidity at high temperatures.
• C. It serves as the main structural component of the phospholipid bilayer.
• D. It is responsible for cell-to-cell recognition.

Answer: (B)

Verified step by step guidance

1. Understand the structure and function of the cell membrane: The cell membrane is primarily composed of a phospholipid bilayer, with embedded proteins, carbohydrates, and cholesterol molecules. Cholesterol plays a specific role in maintaining membrane stability and fluidity.
2. Learn about membrane fluidity: Membrane fluidity refers to the ability of the lipid bilayer to move and adapt its structure. This is crucial for processes like diffusion, signaling, and maintaining the integrity of the cell under varying temperatures.
3. Examine the role of cholesterol at low temperatures: At low temperatures, cholesterol prevents the phospholipids in the bilayer from packing too tightly, which helps maintain fluidity and prevents the membrane from becoming too rigid.
4. Examine the role of cholesterol at high temperatures: At high temperatures, cholesterol interacts with the phospholipids to reduce excessive movement, thereby decreasing fluidity and preventing the membrane from becoming too permeable.
5. Conclude the primary role of cholesterol: Cholesterol acts as a regulator of membrane fluidity, increasing fluidity at low temperatures and decreasing fluidity at high temperatures, ensuring the cell membrane remains functional across a range of conditions.