The respiratory quotient during cellular respiration would depend on

Question

The respiratory quotient during cellular respiration would depend on (A) The nature of enzymes involved (B) The nature of the substrate (C) The amount of carbondioxide released (D) The amount of oxygen utilised

Tardigrade Admin · Accepted Answer

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 eo f C O _{2} e v o l v e d}{V o l u m eo f O _{2} co 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} + 6 O_{2} \to 6 C O_{2} + 6 H_{2} O + E n er g y

R . Q . = \frac{V o l u m eo f C O _{2} e v o l v e d}{V o l u m eo f O _{2} co 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:

2 C_{51} H_{98} O_{6} + 145 O_{2} \to 102 C O_{2} + 98 H_{2} O + E n er g y

R . Q . = \frac{V o l u m eo f C O _{2} e v o l v e d}{V o l u m eo f O _{2} co n s u m e d} = \frac{102}{145} = 0.70

(3) Proteins: When proteins are used as the respiratory substrate like germinating gram, pea, bean, mung seeds, etc. R.Q. value is generally less than one around 0.8-0.9.
(4) 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} + 3 O_{2} \to 4 C O_{2} + 3 H_{2} O + E n er g y

R . Q . = \frac{V o l u m eo f C O _{2} e v o l v e d}{V o l u m eo f O _{2} co n s u m e d} = \frac{4}{3} = 1.33

(5) In xerophytes: When there is incomplete oxidation of carbohydrates as in the respiration of Bryophyllum, Opuntia, etc. R.Q. value is zero as CO₂ is not released during the night time.

2 C_{6} H_{12} O_{6} + 3 O_{2} \to 3 C_{4} H_{6} O_{5} + 3 H_{2} O + E n er g y

R . Q . = \frac{V o l u m eo f C O _{2} e v o l v e d}{V o l u m eo f O _{2} co n s u m e d} = \frac{0}{3} = 0

(6) Anaerobic respiration: Respiration in the absence of O₂ i.e. in anaerobic respiration, R.Q. value is infinity as O₂ is not consumed.

C_{6} H_{12} O_{6} \to Z y ma se 2 C_{2} H_{5} O H + 2 C O_{2} + E n er g y

R . Q . = \frac{V o l u m eo f C O _{2} e v o l v e d}{V o l u m eo f O _{2} co n s u m e d} = \frac{2}{0} = I n f ini t y

Q. The respiratory quotient during cellular respiration would depend on

The nature of enzymes involved

The nature of the substrate

The amount of carbondioxide released

The amount of oxygen utilised