Adjusting Membrane Lipids for Fluidity

Steps:

• Cell membranes lose fluidity in cold due to closer phospholipid packing.
• Unsaturated fatty acids have double bonds creating kinks that disrupt packing and maintain fluidity.
• Increasing unsaturated fatty acids counters cold-induced rigidity.
• Cholesterol molecules insert between phospholipids, buffering against excessive rigidity in low temperatures.

Why A is correct:

• Unsaturated fatty acids lower the membrane's gel-to-liquid transition temperature via kinks from double bonds (definition of unsaturation effect); cholesterol stabilizes fluidity by preventing tight packing (fluid mosaic model principle).

Why the others are wrong:

• B: Omits cholesterol's role in preventing cold-induced rigidity.
• C: Saturated fatty acids lack kinks, increasing rigidity and worsening fluidity loss.
• D: Saturated fatty acids promote tighter packing, reducing fluidity further.

Final answer: A