RESPIRATORY QUOTIENT:

The ratio of volume of CO₂ evolved to the volume of O₂ consumed in respiration is called the respiratory quotient (RQ) or respiratory ratio.

It depends on the type of respiratory substrate.

When carbohydrates are used as respiratory substrate and are completely oxidized, the RQ is 1,

because volume of CO2 evolved is equal to volume of oxygen consumed, as shown in the equation.

When fats or proteins are used as a substrate, the RQ is less than 1, as volume of CO2 evolved is always less than volume of oxygen consumed.

Mostly for fats RQ is about 0.7 and for proteins it is about 0.9.

Calculations for fatty acid, tripalmitin, if used as a substrate are as follows;

 

In case of anaerobic respiration, RQ is always infinity, as CO₂ is evolved without taking O₂.