Fluid-mosaic model: dynamic phospholipid bilayer with embedded, mobile proteins

Steps:

• Recall the fluid-mosaic model by Singer and Nicolson describes the plasma membrane as a flexible phospholipid bilayer with proteins inserted like mosaic tiles.
• Note the "fluid" aspect means lipids and proteins diffuse laterally within the plane of the membrane.
• Examine choices for descriptions matching this dynamic, mosaic structure.
• Select the option highlighting movement of components, which captures the model's essence.

Why D is correct:

• The model defines membranes as fluid, allowing proteins and phospholipids to move and shift positions laterally, as per its foundational 1972 description.

Why the others are wrong:

• A: Cholesterol influences fluidity but is not a core feature of the model's structural description.
• B: Diffusion and osmosis explain permeability, not the membrane's architectural model.
• C: Receptor functions are roles of proteins but do not define the mosaic arrangement or fluidity.

Final answer: D