Question

Respiratory quotient (R.Q.) is defined as the ratio of volume of $C{O}_2$ evolved to the volume of $O_2$ taken in during the respiration process. Value of R.Q. depends on the nature of respiratory substrate and to the extent to which this substance is broken down into simpler products. Which of the following situation will give us the R.Q. value as infinity?

• A. Fats used as substrate under aerobic conditions.
• B. Organic acid is used as a substrate under aerobic conditions.
• C. Any type of substrate used under anaerobic conditions
• D. Any type of substrate used under aerobic conditions.

Answer 1

The correct option is C Any type of substrate used under anaerobic conditions

• Respiratory quotient for carbohydrates is $6/6=1$,
  

because the reaction involves $C_6{H}_{12}{O}_6+6O_2⟶6C{O}_2+12H_{2}O$.

So $6$ carbon and $6$ oxygen are present.

• Respiratory quotient for fat and protein is less than the unity $57/80=0.7$.
  

The reaction includes $C_{57}{H}_{104}{O}_6+80O_2⟶57C{O}_2+52H_{2}O$

So $57$ carbon and $80$ oxygen atoms are present respiratory quotient for protein is $0.9$ which is also less than 1.

• Respiratory quotients for organic acid is more than 1
  

$4/3=1.3$ reaction includes $C_4{H}_{6}O+3O_2⟶4C{O}_2+3H_{2}O$.

• Respiratory quotient for anaerobic respiration is infinity

$C_6{H}_{12}{O}_6+6O_2⟶2C{O}_2+2C_2{H}_{5}OH$ as no oxygen is released
So $rq=2/0=infinity$.
So the correct option is "Any type of substrate used under anaerobic conditions".