Low Melting Points Aid Cold Adaptation

Steps:

• Mammals in cold climates need triglycerides that remain liquid at low temperatures to maintain membrane fluidity and energy storage.
• Saturated fatty acids have higher melting points than unsaturated ones due to straight chains packing tightly; unsaturation introduces kinks that lower melting points.
• Longer chains increase melting points by enhancing van der Waals interactions, while shorter chains reduce them.
• Short chain unsaturated fatty acids thus have the lowest melting points, preventing solidification in cold environments.

Why D is correct:

• Short chain unsaturated fatty acids have the lowest melting points (per lipid packing principles), keeping triglycerides fluid in cold climates for optimal physiological function.

Why the others are wrong:

• A: Long chain saturated fatty acids solidify at high temperatures, unsuitable for cold.
• B: Long chain unsaturated fatty acids have higher melting points than short chain versions due to chain length.
• C: Short chain saturated fatty acids lack unsaturation, raising melting points above unsaturated counterparts.

Final answer: D