Which statement most accurately describes the relationship between the permeability and fluidity properties of phospholipid bilayers and their structure? a. bilayers are most permeable and most fluid when they consist of longer, unsaturated hydrocarbon tails. b. bilayers are most permeable and most fluid when they consist of longer, saturated hydrocarbon tails. c. bilayers are most permeable and most fluid when they consist of shorter, unsaturated hydrocarbon tails. d. bilayers are most permeable but least fluid when they consist of shorter, unsaturated hydrocarbon tails.

Answer;

A. Bilayers are more permeable as well as more fluid when they consist of shorter, unsaturated hydrocarbon tails.  

Explanation;The lipid bilayer of cell membranes is arranged in two layers of phospholipids with the hydrophilic heads forming the outer edges and the tails forming the interior. In this arrangement, the bilayer has a hydrophobic core that prevents the passage of polar molecules while allowing the relatively free diffusion of non-polar molecules.The ratio of saturated and unsaturated fatty acids determines the fluidity in the membrane at cold temperatures. When unsaturated fatty acids are compressed, the “kinks” in their tails push adjacent phospholipid molecules away, which helps maintain fluidity in the membrane.