Bioenergetics insight: Fats (triacylglycerols) yield more energy upon oxidation than simple sugars primarily because they contain many more ________.

Introduction / Context: When comparing caloric yields, fats provide roughly 9 kcal/g, while carbohydrates provide about 4 kcal/g. The biochemical reason lies in oxidation states and the number of energy-rich C–H bonds available for oxidative metabolism.

Given Data / Assumptions:

• Fats (triacylglycerols) are highly reduced hydrocarbons with few heteroatoms.
• Simple sugars (e.g., glucose) contain multiple oxygen atoms and are partially oxidized.
• Energy yield tracks the degree of reduction.

Concept / Approach: Oxidation of C–H bonds transfers electrons to cofactors (NAD+/FAD), generating reduced equivalents that drive ATP synthesis. The more reduced (hydrogen-rich) the substrate, the greater the electron yield and hence energy produced.

Step-by-Step Solution: Compare composition → fats are rich in C–H, poor in O; sugars have many C–O bonds. Relate to redox → more C–H bonds = more electrons available for oxidative phosphorylation. Infer energy outcome → fats deliver more ATP per gram than sugars. Thus, “hydrogen atoms in reduced C–H bonds” is the key reason.

Verification / Alternative check: Standard metabolic calculations show palmitate oxidation yields far more ATP than glucose on a per-carbon basis due to its higher reduction state.

Why Other Options Are Wrong: Total carbon count (option A) misses the redox point; “more covalent bonds” (option C) is vague since sugars also have many covalent bonds; hydrogen bonds (option D) and ionic bonds (option E) are irrelevant to oxidative yield.

Common Pitfalls: Equating molecular size with energy directly; ignoring the role of existing oxygen atoms in carbohydrates that reduce further electron yield.

Final Answer: hydrogen atoms bound in reduced C–H bonds.