A cell membrane is composed of phospholipids with varying degrees of unsaturation. How does this affect membrane fluidity?

• A. Saturation level does not affect membrane fluidity.
• B. Saturated fatty acids increase membrane fluidity by preventing tight packing.
• C. Unsaturated fatty acids decrease membrane fluidity by allowing tight packing.
• D. Unsaturated fatty acids increase membrane fluidity by preventing tight packing.

Answer: (D)