Fluid mosaic model—dimensionality and composition According to the fluid mosaic model, a biological membrane is best described as:

Introduction / Context:The fluid mosaic model unifies how lipids and proteins are arranged and move within membranes, explaining selective permeability, lateral diffusion, and dynamic organization.

Given Data / Assumptions:

• Membranes are lipid bilayers with embedded proteins.
• Lipids and many proteins diffuse laterally (2D fluid).
• Carbohydrates decorate proteins and lipids extracellularly but do not dominate structure.

Concept / Approach:“Two-dimensional solution” emphasizes lateral mobility within the plane of the bilayer. Proteins are mosaically distributed and can drift or be corralled, while lipids provide a continuous matrix. Vertical (3D) diffusion across the bilayer is restricted.

Step-by-Step Solution:Identify the dimensionality of primary diffusion: two-dimensional.Recall composition: oriented lipids form the bilayer; globular proteins are embedded and peripheral.Select the option that matches these features.

Verification / Alternative check:FRAP experiments demonstrate lateral diffusion, supporting the 2D fluid paradigm.

Why Other Options Are Wrong:

• 3D solutions: Misstate the dominant lateral dynamics.
• Carbohydrate-only models: Ignore integral proteins and lipids.
• Rigid lattice: Inconsistent with fluidity observed experimentally.

Common Pitfalls:Assuming proteins are static or evenly distributed; microdomains and fences influence mobility.

Final Answer:A two-dimensional solution of oriented lipids with interspersed globular proteins.