Respiratory Quotient

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

\[\mathrm{RQ=\frac{Volume~ofCO_{2}~evolved}{Volume~ofO_{2}~consumed}}\]

• Respiratory Quotient (RQ) is the ratio of volume of CO₂ evolved to volume of O₂ consumed during aerobic respiration. Formula: RQ = Volume of CO₂ evolved ÷ Volume of O₂ consumed.
• For carbohydrates - RQ = 1 (equal volumes of CO₂ and O₂); e.g., glucose: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + Energy.
• For fats - RQ is less than 1 (more O₂ needed for oxidation); e.g., Tripalmitin: RQ = 102/145 = 0.7.
• For proteins, RQ is approximately 0.9.
• In living organisms, multiple substrates are respired together (not pure fats or proteins), so RQ is often more than 1; pure fats or proteins are never the sole respiratory substrate.