Describe : Respiratory Quotient.

Explanation

During aerobic respiration, `O_(2)` is consumed and `CO_(2)` is released.
The ratio of the volume of `CO_(2)` evolved to the volume of `O_(2)` consumed in respiration is called the respiratory quotient.
`RQ = ("Volume of " CO_(2) "evolved ")/("Volume of "O_(2) " consumed ")`
The respiratory quotient depends upon the type of respiratory substrated used during respiration.
RQ of Carbohydrates : When carbohydrates are used as substrate and are completely oxidised, the RQ will be 1, because amounts of `CO_(2) and O_(2)` are evolved and consumed.
Equation : `C_(6) H_(12) O_(6) + 6O_(2) to 6CO_(2) + 6H_(2) O ` + Energy
`RQ = (6 CO_(2))/( 6O_(2)) = 1.0`
RQ of fat : When fats are used in respiration, the RQ used than 1. Calculation for a fatty acid, tripalmitin, if used as a substrate is shown.
`2(C_(51) H_(98)O_(6)) + 145O_(2) to 102 CO_(2) + 98 H_(2) O` + Energy
`RQ = (102 CO_(2))/(145 O_(2))` = 0. 7
Protein : When proteins are respiratory substrates the ratio would be about 0.9.
When organic acid is used for respiration the RQ remain above 1.
e.g. equation for respiration of oxalic acid :
`2 (CO OH)_(2) +O_(2) to 4CO_(2) + 2H_(2) O` Energy
`RQ = (4 CO_(2))/( 1 O_(2))` = 4
Note : In living organisms respiratory substrates are often more than one , pure proteins or fats are never usedas respiratory substrates.