Saturated Fatty Acids Stabilize Membrane Fluidity

Steps:

• Recall that membrane fluidity depends on phospholipid tail interactions; tighter packing reduces fluidity.
• Identify that fatty acid saturation affects tail shape: saturated chains are straight, unsaturated have kinks.
• At high temperatures, phospholipids move more, increasing fluidity; components promoting tight packing counteract this.
• Conclude saturated fatty acids best reduce fluidity by enabling close packing.

Why C is correct:

• Saturated fatty acids lack double bonds, forming straight hydrocarbon chains that pack tightly via van der Waals forces, reducing fluidity as defined by the fluid mosaic model.

Why the others are wrong:

• A: Phosphate groups are polar heads that interact with water, not influencing tail packing or fluidity.
• B: Unsaturated fatty acids have double bonds creating kinks, which disrupt packing and increase fluidity.
• D: Proteins embed in the membrane for transport or signaling but do not alter phospholipid tail saturation or fluidity.

Final answer: C