Membrane Fluidity from Lipid Components

Steps:

• Identify key factors in fluid mosaic model: phospholipid tails and cholesterol affect membrane fluidity.
• Unsaturated fatty acid chains create kinks, preventing tight packing and increasing fluidity.
• Cholesterol inserts between phospholipids, modulating fluidity by disrupting packing at various temperatures.
• Match to diagram: components 4 (unsaturated tails) and 6 (cholesterol) directly enhance fluidity.

Why D is correct:

• Unsaturated tails (4) and cholesterol (6) increase fluidity per the fluid mosaic model, where kinks in unsaturated chains and cholesterol's buffering effect maintain membrane flexibility.

Why the others are wrong:

• A: 1 (likely proteins) and 3 (saturated tails) reduce fluidity by stabilizing structure and allowing tight packing.
• B: 2 (phospholipid heads) and 4 (unsaturated tails) mix hydrophilic and hydrophobic roles, but heads don't directly affect fluidity.
• C: 3 (saturated tails) and 5 (possibly glycoproteins) decrease fluidity through straight chains and rigid attachments.

Final answer: D