The fluidity of a bilayer is generally increased by:

• A. The binding of water to the fatty acyl side chains.
• B. An increase in fatty acid chain length.
• C. An increase in the number of double bonds in the fatty acid hydrocarbon chains.
• D. A decrease in temperature.

Answer: (C)

Verified step by step guidance

1. Understand that the fluidity of a lipid bilayer is influenced by the structure and composition of the fatty acids in the bilayer.
2. Recognize that double bonds in fatty acid chains introduce kinks, preventing tight packing of the lipids, which increases fluidity.
3. Consider that longer fatty acid chains have more van der Waals interactions, leading to decreased fluidity.
4. Note that lower temperatures generally decrease fluidity as molecular motion is reduced.
5. Conclude that an increase in the number of double bonds in the fatty acid hydrocarbon chains increases bilayer fluidity by disrupting tight packing.