Which statement best describes the implication of unsaturation in fatty acids?

• A. Saturated fatty acids pack more tightly than unsaturated fatty acids
• B. Unsaturated fatty acids pack more tightly than saturated fatty acids
• C. Degree of unsaturation directly measures membrane thickness
• D. Unsaturated fats always have higher melting points than saturated fats

Answer: (B)

Unsaturation in fatty acids introduces cis double bonds that create kinks in the hydrocarbon tails. Those bends prevent the tails from lining up neatly, so the molecules can’t pack together as tightly as saturated (straight) chains. Because packing is looser, there are fewer strong van der Waals interactions holding the tails together, which lowers the energy needed to melt the fat and generally makes membranes more fluid at a given temperature.

In contrast, saturated fatty acids have straight chains that align closely, packing tightly and increasing melting points, which tends to make membranes more rigid. So the key implication of unsaturation is looser packing and lower melting points, not tighter packing or greater membrane thickness.