Respiratory Quotient

During aerobic respiration, O2 is consumed and CO2 is released. The ratio of the volume of CO2 evolved to the volume of O2 consumed in respiration is called the respiratory quotient (RQ) or respiratory ratio:

RQ = volume of CO₂ evolved / volume of O₂ consumed

The respiratory quotient depends upon the type of respiratory substrate used during respiration:

• When carbohydrates are used as substrate and are completely oxidised, the RQ will be 1, because equal amounts of CO2 and O2 are evolved and consumed respectively:

C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + Energy, RQ = 6CO₂ / 6O₂ = 1.0

• When fats are used in respiration, the RQ is less than 1. For the fatty acid tripalmitin used as a substrate:

2 (C₅₁H₉₈O₆) + 145O₂ → 102CO₂ + 98H₂O + energy, RQ = 102CO₂ / 145O₂ ≈ 0.7

• When proteins are the respiratory substrates, the ratio would be about 0.9. …