This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: General anatomy, Subject name: Anatomy
Function of cholesterol in plasmalemma is to 
Select and explain. 
A. Increase the fluidity of lipid bilayer, B. Decrease the fluidity of lipid bilayer, C. Facilitate the diffusion of ions into the lipid bilayer, D. Assist in the transpo of hormones across the lipid bilayer
B: Decrease the fluidity of lipid bilayer
Answer: B: Decrease the fluidity of lipid bilayer 
Explanation: The fluidity of the lipid bilayer is decreased in following three ways Lowering temperature Increasing saturation of fatty acyl tails in phospholipid membrane Increase membrane cholesterol content. Cholesterol interacts with the phospholipid membrane containing fatty acyl chains, compacting them, constraining the motion in bilayers, hence decreasing the fluidity. Ref: Lehninger 30e pg 395.