Question

Respiratory quotient of respiratory substrate $C_{39}H_{72}O_6$ ​would be
A. 1.34
B. 0.718
C. 3.25
D. 2.71

Answer 1

Hint: The ratio of carbon dioxide released to the oxygen absorbed (in terms of volume) is called the Respiratory Quotient, which can be abbreviated as RQ. The respiratory quotient can also be called the respiratory ratio or respiratory coefficient. The substrate is oxidized by aerobic respiration resulting in the evolution of carbon dioxide.
Complete step-by-step answer: RQ for carbohydrates is 1, RQ for proteins may be in the range of 0.8 to 0.9, RQ for fats is always lower than 1, RQ of organic acids is always higher than 1, and the RQ for a mixture of substrates is 0.8.
${\rm{RQ}} = \dfrac{{{\rm{CO_2~liberated}}}}{{{\rm{O_2~absorbed}}}}$
C₃₉H₇₂O₆ ​+ 54O₂ ​ gives 39CO₂ ​+ 36H₂O
So Respiratory quotient of $\dfrac{{39CO_2}}{{54O_2}} = 0.72$
So the correct answer is '0.718'.
Therefore, the correct answer is option B .
Additional Information: Usually, more oxidized molecules (for example, glucose) need less oxygen to metabolize completely and, therefore, have a higher RQ. Contrarily, less oxidized molecules (for example, fatty acids) need more oxygen for their full metabolism and hence they have a lower RQ. The RQ value corresponds to a caloric value for each liter of carbon dioxide produced. If oxygen consumption numbers are available, they are used directly, since they are more direct and reliable estimations of energy production.
Note: RQ can be used to analyze the gain of weight in type-2 diabetes patients. Studies have shown that patients who are on oral hypoglycemic agents and who have a higher BMI have a higher RQ ratio than people with a normal BMI.