Question

The respiratory quotient (R.Q) of some of the compounds is 4, 1 and 0.7. These compounds are identified respectively as
A) Malic acid, palmitic acid and tripalmitin
B) Oxalic acid, carbohydrate and tripalmitin
C) Tripalmitin, malic acid and carbohydrate
D) Palmitic acid, carbohydrate and oxalic acid
E) Oxalic acid, carbohydrate and malic acid

Answer 1

It is determined from the ratio of the body's produced carbon dioxide to the body's absorbed oxygen. One, zero and more or less than one will be its value.

Complete answer:
First we should know about respiratory quotient (R.Q) to answer this question. When measured from the output of carbon dioxide, the respiratory quotient ( RQ ) is a dimensionless number used in basal metabolic rate (BMR) measurements.
RQ=$\dfrac {CO_2\,eliminated}{ O_2 consumed}$
Now, let us find the solution from the options-
In aerobic conditions, as the organic acids break down as a respiratory substrate, the RQ value is greater than 1 i.e., Oxalic acid-4, carbohydrate-1. As organic acids carry more oxygen and thus need fewer oxygen for their oxidation. In aerobic conditions, if the respiratory substrates are fats or proteins, the RQ value is less than 1 such as Tripalmitin-0.7. Fats here contain far fewer atoms of oxygen in proportion to carbon and hydrogen atoms. Thus, carbon dioxide emitted during fat oxidation is less than oxygen used, giving less than one to R.Q.From these we came to know that options A, C, D and E are incorrect options.

Thus, the correct answer is option ‘B’ Oxalic acid, carbohydrate and tripalmitin.

Note: It must be remembered that the respiratory quotient is hardly one in living organisms; in fact, most frequently it appears to be more than one. Quite simply, pure proteins and fats are never used as respiratory substrates. Significance of RQ is it helps to define the respiratory substratum and also helps to understand the type of respiration that is carried out.