Question

Maximum energy per gram on oxidation is yielded from

• A. Starch
• B. Fat
• C. Glycogen
• D. Protein

Hint:

Fats provide more energy per gram than carbohydrates or proteins due to their higher carbon-hydrogen content.

Answer 1

The Correct Option is B

Step 1: Understanding energy yield.
Fat yields the highest amount of energy per gram upon oxidation compared to carbohydrates and proteins. This is because fats are more reduced, containing more hydrogen atoms, which produce more energy when oxidized.
Step 2: Analyzing the options.
(1) Starch: Starch is a carbohydrate and yields less energy per gram compared to fats.
(2) Fat: Correct — Fats contain more carbon-hydrogen bonds, which release more energy during oxidation.
(3) Glycogen: Glycogen is a polysaccharide but provides less energy per gram than fats.
(4) Protein: Proteins provide less energy per gram than fats and are not the preferred energy source.
Step 3: Conclusion.
The correct answer is (2) Fat, as it provides the most energy per gram during oxidation.

Answer 2

Energy yield on oxidation depends on how reduced a molecule is, since more reduced carbon atoms release more energy when fully oxidized to CO2. Comparing each option on that basis:

1. Starch: Starch is a glucose polymer, and glucose carbons are already partially oxidized, so its oxidation releases comparatively less energy per gram.
2. Fat: Fats are built mainly of long hydrocarbon chains in their fatty acid tails, which are highly reduced; oxidizing these releases substantially more energy per gram than an equivalent mass of carbohydrate.
3. Glycogen: Glycogen, like starch, is a glucose polymer with the same partially oxidized carbon backbone, so it yields energy per gram similar to other carbohydrates and less than fat.
4. Protein: Proteins are broken down into amino acids, whose carbon skeletons are moderately reduced but also carry nitrogen that must be removed and processed separately, and their overall energy yield per gram falls below that of fat.

Because fat's hydrocarbon-rich composition makes it the most reduced of these four fuel sources, it releases the most energy per gram when fully oxidized.

Therefore, the correct answer is fat.