Biology Biomolecules MDCAT 2019
PMDC Verified Question 121 of 142
Lipids contain double amount of energy as compared to the same amount of carbohydrates due to the presence of:
A
Lower proportion of C-H bonds
B
Higher proportion of C-O bonds
C
Higher proportion of C-H bonds
D
Higher proportion of oxygen
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option C: Higher proportion of C-H bonds
Concept:

Biological energy yield is fundamentally determined by the oxidation state of the carbon atoms in a molecule.

Solution:

  • The chemical energy harvested during cellular respiration comes from stripping high-energy electrons away from non-polar Carbon-Hydrogen (C-H) bonds.


  • Lipids (fatty acids) consist of massive, long hydrocarbon tails almost entirely composed of these C-H bonds, with very little oxygen present.


  • Because they possess a vastly higher proportion of C-H bonds compared to carbohydrates (which are already partially oxidized with many C-O bonds), lipids yield more than double the energy upon complete oxidation (~9 kcal/g vs ~4 kcal/g).


Why other options are incorrect:

  • Higher proportion of C-O / Oxygen: This describes carbohydrates. Molecules with high oxygen content are already partially oxidized, meaning they have less potential energy left to release.


  • Lower proportion of C-H bonds: The direct opposite of reality.

Quality & Fidelity Assurance: Every question on BeambePrep is rigorously curated against the official PMDC syllabus with zero filler, zero out-of-syllabus content, and zero typos. When an authentic past paper originally contained a historical mistake or ambiguity from the examining board (such as UHS or NUMS), BeambePrep faithfully reflects the original paper while detailing the nuance and scientific consensus in the autopsy above.

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