Question

Given below are two statements, one is labelled as Assertion (A) and other one labelled as Reason (R).
Assertion (A) : Respiration quotient of protein is 0.8 to 0.9.
Reason (R) : Respiration quotient is less than 1 as respiratory substrate is highly reduced.
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:

Remember the standard RQ values for competitive exams:
- Carbohydrates: \(\text{RQ} = 1.0\)
- Proteins: \(\text{RQ} = 0.8 \text{ to } 0.9\)
- Fats/Lipids: \(\text{RQ} \approx 0.7\)
- Organic Acids (e.g., malic acid): \(\text{RQ} > 1.0\) (due to high oxygen content)

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
The Respiratory Quotient (RQ) is a dimensionless ratio used to determine the nature of the metabolic substrate being oxidized during respiration.
It is defined as the ratio of the volume of carbon dioxide (\(\text{CO}_2\)) released to the volume of oxygen (\(\text{O}_2\)) consumed over a given period.
\[ \text{RQ} = \frac{\text{Volume of } \text{CO}_2 \text{ eliminated}}{\text{Volume of } \text{O}_2 \text{ consumed}} \] The value of RQ depends entirely on the chemical composition of the substrate undergoing aerobic respiration.

Step 2: Detailed Explanation:
When carbohydrates are completely oxidized, the volume of \(\text{CO}_2\) released equals the volume of \(\text{O}_2\) consumed, resulting in an \(\text{RQ} = 1.0\).
This is because carbohydrates have a balanced ratio of oxygen to hydrogen and carbon.
In contrast, proteins and fats are highly reduced compounds that contain relatively little oxygen in their molecular structure.
Because of this, their complete oxidation requires a much larger amount of external oxygen relative to the amount of carbon dioxide produced.
For proteins, the average RQ value ranges from \(0.8\) to \(0.9\).
For lipids (fats), the RQ value is even lower, typically around \(0.7\).
Therefore, Assertion (A) is correct because the respiratory quotient of proteins is indeed in the range of \(0.8\) to \(0.9\).
Reason (R) is also correct because the highly reduced state of protein and fat molecules necessitates more oxygen consumption, bringing the RQ value below \(1.0\).
Since this chemical composition is the direct cause of the lower RQ value, Reason (R) is the correct explanation of Assertion (A).

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