Question

Respiratory quotient is more than one when the substrate is ___.
A. Protein
B. Fat
C. Organic acid
D. Glucose

Answer 1

Hint: A respiratory quotient (RQ) is a logarithmic number used to calculate basal metabolic rate by the ratio of carbon dioxide liberated to oxygen absorbed. With the help of an instrument called a respirometer, we can detect the respiratory quotients of different substrates. RQ can be calculated for a specific substrate such as protein, sugar, or lipids.
Complete step-by-step answer: The RQ of the body is almost 1 which confirms the volume of oxygen absorbed is the same as that of the carbon dioxide released. If it is more than 1, it indicates the amount of oxygen absorbed is less than the carbon dioxide generated, and if RQ is less than 1, it indicates the amount of oxygen absorbed is more than the amount of carbon dioxide released.
When carbohydrates are used as the substrate, the amount of carbon dioxide evolved is the same as that of the amount of oxygen absorbed. So, RQ for carbohydrates is 1. In the case of protein as substrates, the oxygen absorbed is more than the carbon dioxide released. RQ for proteins may be in the range of 0.8 to 0.9.
Similarly, in the case of fats, the oxygen absorbed is more than the carbon dioxide released. So RQ for fats is always lower than 1. However, when the substrates are organic acids, the amount of oxygen absorbed is lesser than the amount of carbon dioxide released. So, the RQ of organic acids is always higher than 1.
Therefore, the correct answer is option C- Organic acid.
Note: The RQ of chronic obstructive pulmonary disease (COPD) patients can be reduced by increasing the fat content of their food. This will reduce the burden of removing carbon dioxide from their bodies.