A Levels Biology (9700)•9700/13/M/J/19
Explanation
Classifying triglycerides by fatty acid saturation
Steps:
- Identify saturation: saturated fatty acids lack double bonds; unsaturated have one or more.
- Analyze first triglyceride: composed of X (straight chain, no double bonds), Y (straight, no double bonds), Z (straight, no double bonds), all saturated.
- Analyze second triglyceride: composed of X (kinked chain, double bond) and Y (kinked, double bond), both unsaturated.
- Analyze third triglyceride: includes at least three distinct saturated chains labeled X and Y (implying additional one), more than two different saturated fatty acids.
Why A is correct:
- Matches definitions: first has all three saturated (X, Y, Z); second has two unsaturated (X, Y); third exceeds two saturated types (X, Y, plus implied third).
Why the others are wrong:
- B: Misassigns Z as unsaturated and limits saturated to only X, Y.
- C: Incorrectly labels Z as both saturated and unsaturated; miscounts saturated types.
- D: Falsely limits saturated to only Z and expands unsaturated/mixed saturated incorrectly.
Final answer: A
Topic: Carbohydrates and lipids
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