Respiratory Quotient - A short Study

RESPIRATORY QUOTIENT

• During the process of  aerobic respiration, the oxygen  is consumed and carbon dioxide is released.

• The ratio of the volume of carbon dioxide released  to the volume of oxygen used  in respiration is called the respiratory quotient (RQ) or respiratory ratio.

• RQ = volume of carbon dioxide released / volume of oxygen used 

• The respiratory quotient depends mainly on the respiratory substrate used during respiration. 

Carbohydrates used as respiratory substrate

• When carbohydrates are used as substrates then carbohydrates  are completely oxidised during respiration therefore  the RQ for carbohydrates is one.

• During the oxidation of carbohydrates, equal amounts of Carbon dioxide  and oxygen are evolved and consumed respectively.

• During the oxidation of carbohydrates, six molecules of carbon dioxide are released and six molecules of oxygen are used.

C6H12O6 + 6O2 → 6CO2 + 6H2O

      RQ=6CO2/6O2 =1

Fat used as respiratory substrate

• When fats  are used as substrates then  the RQ for fats is less than one .

• During the oxidation of a fat like tripalmitin,102 molecules of carbon dioxide are released and 145 molecules of oxygen are used.

C51H98O6 + 102O2 → 198CO2 + 98H2O

   RQ=102CO2/198O2 =0.7

Protein used as respiratory substrate

• When proteins  like Albumin are used as the  respiratory substrates the  RQ is about 0.88. 

C72H112N18O22S +77 O2 →63CO2 + 38H2O + SO3+ 9CO(NH2)2

RQ=77CO2/63O2 =0.88

• For Ideal respiratory substrate in living organisms, respiratory quotients  are often more than one therefore pure proteins or fats are never used as respiratory substrates.

• Respiratory Quotient can be used as an indicator  of feeding habits . If the feeding habit is under control then it  stimulates the body to utilize  the fat stored inside the body.

• As a result ,the RQ will less than the  respiratory quotient. In case of over feeding, the body encourages the synthesis of fat .

• Underfeeding is marked by a respiratory quotient below 0.85, while a respiratory quotient greater than 1.0 indicates overfeeding.