Question

The right relationship between the value of Respiratory Quotient is

• A. Glucose $>$ Fats $>$ Organic acid
• B. Glucose $ < $ Fats $ < $ Organic acid
• C. Fats $>$ Glucose $>$ Organic acid
• D. Fats $ < $ Glucose $ < $ Organic acid

Answer 1

Answer: (D)

Respiratory Quotient:
R.Q. is the ratio of the volume of carbon dioxide released to the volume of oxygen taken in respiration and it is mathematically expressed as:
$R.Q.=\frac{V o l u m e o f C O_{2} e v o l v e d}{V o l u m e o f O_{2} c o n s u m e d}$
The value of R.Q. varies with the substrate. Thus the measurement of R.Q. gives some idea of the nature of the substrate being respired in a particular tissue. R.Q. is usually measured by Ganong's respirometer.
(1) Carbohydrates: When carbohydrates are used as the respiratory substrate like germinating wheat, rhizomes, tubers, paddy grains, or green leaves kept in the dark, etc. R.Q. value is unity.
$C_{6}H_{12}O_{6}+6O_{2} \rightarrow 6CO_{2}+6H_{2}O+Energy$
$R.Q.=\frac{V o l u m e o f C O_{2} e v o l v e d}{V o l u m e o f O_{2} c o n s u m e d}=\frac{6}{6}=1$
(2) Fats/Oils: When fats or oils are used as the respiratory substrate like germinating linseed, castor, mustard, til seeds, etc. R.Q. value is generally less than one around 0.7. For example, in the case of tripalmitin, the reaction can be written as follows:
$2C_{51}H_{98}O_{6}+145O_{2} \rightarrow 102CO_{2}+98H_{2}O+Energy$
$R.Q.=\frac{V o l u m e o f C O_{2} e v o l v e d}{V o l u m e o f O_{2} c o n s u m e d}=\frac{102}{145}=0.70$
(3) Organic acids: When organic acids are used as the respiratory substrate like malic acid, oxalic acid, etc. R.Q. value is generally more than one. The breakdown of malic acid is as follows:
$C_{4}H_{6}O_{5}+3O_{2} \rightarrow 4CO_{2}+3H_{2}O+Energy$
$R.Q.=\frac{V o l u m e o f C O_{2} e v o l v e d}{V o l u m e o f O_{2} c o n s u m e d}=\frac{4}{3}=1.33$