Question

Given below are two statements, one is labelled as Assertion (A) and other one labelled as Reason (R).
Assertion (A) : Fatty acids conserve more energy than that of carbohydrates
Reason (R) : Fatty acid contain more reduced form of carbon in their structure than that of carbohydrates.
In light of the above statements, choose the correct answer from the options given below.

• A. Both (A) and (R) are true and (R) is the correct explanation of (A).
• B. Both (A) and (R) are true but (R) is NOT the correct explanation of (A).
• C. (A) is true but (R) is false.
• D. (A) is false but (R) is true.

Hint:

Carbon oxidation rule:
The more hydrogen atoms a carbon is bonded to (the more reduced it is), the more energy it yields upon oxidation.
Hydrocarbons (fats) \(\rightarrow\) Highly reduced \(\rightarrow\) Max energy (\(9 \text{ kcal/g}\)).
Carbohydrates \(\rightarrow\) Partially oxidized \(\rightarrow\) Less energy (\(4 \text{ kcal/g}\)).

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Living organisms obtain metabolic energy by oxidizing organic nutrient molecules.
The amount of energy released per gram of substrate depends on the oxidation state of its carbon atoms.

Step 2: Detailed Explanation:
- Assertion (A) is true:
Fats (lipid/fatty acids) are highly concentrated energy stores.
The complete oxidation of fatty acids yields approximately \(9 \text{ kcal/g}\) of energy, which is more than double the energy yielded by carbohydrates (approximately \(4 \text{ kcal/g}\)).
- Reason (R) is true:
In carbohydrates (like glucose, \(\text{C}_6\text{H}_{12}\text{O}_6\)), most carbon atoms are already partially oxidized because they are bonded to oxygen as alcohol groups (\(-\text{CHOH}-\)).
In contrast, the long hydrocarbon chains of fatty acids consist almost entirely of methylene groups (\(-\text{CH}_2-\)), where the carbons are in a highly reduced state.
Because the carbon atoms in fatty acids are more reduced, they release significantly more hydrogen atoms and electrons during complete oxidation to \(\text{CO}_2\) and \(\text{H}_2\text{O}\).
These electrons feed into the mitochondrial electron transport chain, generating a larger proton-motive force and producing much more ATP.
Thus, the more reduced structure of fatty acid carbons (R) is the direct chemical explanation for why they conserve more energy than carbohydrates (A).

Step 3: Final Answer:
Both (A) and (R) are true, and (R) is the correct explanation of (A).