The fluid mosaic model describes membranes as being composed of which components?

• A. Lipids and proteins arranged in a rigid lattice
• B. A single-layer lipid sheet with no proteins
• C. Lipids, proteins, and carbohydrates in a fluid mosaic
• D. Proteins embedded in a dense protein matrix

Answer: (C)

The main idea being tested is that membranes are dynamic, mixed structures where several different components coexist and can move within the plane of the membrane. In the fluid mosaic model, the membrane is a phospholipid bilayer with proteins interspersed throughout and carbohydrates attached to some lipids and proteins on the extracellular surface. The lipids form the flexible barrier, proteins provide channels, transporters, and receptors, and carbohydrates (as glycoproteins and glycolipids) contribute to cell recognition and interaction. The “fluid” part means these components can diffuse laterally, not be locked in a rigid arrangement, which is why the model is called a mosaic of diverse parts.

This is the best description because it accurately captures all three component types and the flexible, dynamic nature of membranes. The other ideas imply a rigid lattice, a single-layer lipid sheet, or a dense protein matrix, none of which reflect the true, fluid, mixed composition of cellular membranes.