USA Biology Olympiad (USABO) Practice Exam

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Which component is a key part of the cell membrane structure?

Cholesterol
Cellulose
Starch
Amino acids

The correct answer is: Cholesterol

Cholesterol plays a crucial role in the structure of cell membranes. It is located within the phospholipid bilayer and contributes to membrane fluidity and stability. This is important because a fluid membrane is essential for the proper functioning of membrane proteins and for the movement of materials in and out of the cell. Cholesterol helps to prevent the fatty acid chains of the phospholipids from packing too closely together, which can compromise the flexibility of the membrane under varying temperatures. In contrast, cellulose and starch are both polysaccharides that serve different functions, primarily in providing structural support (in the case of cellulose, in plants) or energy storage (in the case of starch, in plants). Amino acids are the building blocks of proteins and do not form a structural component of the cell membrane directly. While proteins embedded in the membrane are essential for functionality, cholesterol is specifically integral to the structural properties of the membrane itself.