Fatty Acid Shape and Membrane Fluidity

Steps:

• Identify elaidic acid as trans-unsaturated (straight chain) and oleic acid as cis-unsaturated (kinked chain).
• Recall that straight chains pack tightly, reducing fluidity; kinked chains pack loosely, increasing fluidity.
• At low temperatures, tight packing solidifies the membrane faster, decreasing fluidity.
• Match to options: elaidic fits closely (less fluid), oleic does not (more fluid).

Why C is correct:

• Trans fats like elaidic align linearly, maximizing van der Waals interactions for tighter packing and lower fluidity per fluid mosaic model.

Why the others are wrong:

• A: Reverses both effects; elaidic packs tightly, not loosely.
• B: Swaps fluidity outcomes; elaidic reduces, not increases, fluidity.
• D: Inverts fitting and fluidity; elaidic fits closely for less, not more, fluidity.

Final answer: C