The mosaic in fluid mosaic model refers to embedded proteins scattered in the phospholipid bilayer

Steps:

• Recall the fluid mosaic model: a dynamic structure with phospholipids forming a fluid bilayer and proteins embedded like tiles in a mosaic.
• Identify "mosaic" aspect: it describes the irregular, varied arrangement of proteins and other components within the lipid layer, not patterns from lipids alone.
• Evaluate options: A and B focus on lipids/cholesterol movement or distribution, ignoring proteins; C suggests regularity, which contradicts the model's irregularity; D matches the protein scattering.
• Confirm D aligns with the definition of mosaic as diverse, embedded elements.

Why D is correct:

• The mosaic part, per the Singer-Nicolson model, denotes the diverse proteins scattered irregularly within the phospholipid bilayer, creating a patchwork effect.

Why the others are wrong:

• A: Phospholipid movement contributes to fluidity, not mosaic patterns.
• B: Cholesterol stabilizes the membrane but does not form the mosaic; proteins do.
• C: The arrangement is irregular, not a regular pattern of heads and proteins.

Final answer: D