11th Class Biology Respiration In Plants Respiratory Quotient / Respiration Ratio

Respiratory Quotient / Respiration Ratio

Category : 11th Class

R.Q. is the ratio of the volume of $C{{O}_{2}}$released to the volume of oxygen taken in respiration and is written as

$R.Q.=\frac{Volume\,of\,C{{O}_{2}}\,evolved}{Volume\,of\,{{O}_{2}}\,absorbed}=\frac{C{{O}_{2}}}{{{O}_{2}}}$

R.Q. is usually measured by Ganong's respirometer.

(1) When carbohydrates are the respiratory substrate (=germinating wheat, oat, barley, paddy grains or green leaves kept in dark or tubers, rhizomes, etc.)

$\underset{\text{Glucose}}{\mathop{{{C}_{6}}{{H}_{12}}{{O}_{6}}}}\,+6{{O}_{2}}\to 6C{{O}_{2}}+6{{H}_{2}}O;\,\,\frac{C{{O}_{2}}}{{{O}_{2}}}=\frac{6}{6}=1$  (Unity)

(2) When fats are the respiratory substrate (=germinating castor, mustard, linseed, til seeds) for fatty substances R.Q. is generally less than one .

(i) $\underset{\text{Stearic}\,\text{acid}}{\mathop{{{C}_{18}}{{H}_{36}}{{O}_{2}}}}\,+26{{O}_{2}}\to 18C{{O}_{2}}+18{{H}_{2}}O;\frac{C{{O}_{2}}}{{{O}_{2}}}=\frac{18}{26}=0.7$(Less than unity)

(ii) $\underset{\text{Tripalmitin}}{\mathop{2{{C}_{51}}{{H}_{98}}{{O}_{6}}}}\,+145{{O}_{2}}\to 102C{{O}_{2}}+98{{H}_{2}}O;\frac{C{{O}_{2}}}{{{O}_{2}}}=\frac{102}{145}=0.7$ (Less than unity)

(3) When protein are the respiratory substrate (=germinating gram, pea, bean, mung seeds)

value of R.Q. is less than unity (0.5-0.9).

(4) When organic acids are the respiratory substrate

(i)$\underset{\text{Malic}\,\text{acid}}{\mathop{{{C}_{4}}{{H}_{6}}{{O}_{5}}}}\,+3{{O}_{2}}\to 4C{{O}_{2}}+3{{H}_{2}}O;\frac{C{{O}_{2}}}{{{O}_{2}}}=\frac{4}{3}=1.33$ (More than unity)

(ii) $\underset{\text{Oxalic}\,\text{acid}}{\mathop{2{{(COOH)}_{2}}}}\,+{{O}_{2}}\to 4C{{O}_{2}}+2{{H}_{2}}O;\frac{C{{O}_{2}}}{{{O}_{2}}}=\frac{4}{1}=4$ (More than unity)

Some other organic acids and their R.Q. are – Succinic acid (1.14), Taurtric acid (1.6) and Acetic acid (1).

(5) When there is incomplete oxidation of carbohydrates (In the respiration of succulents i.e., Bryophyllum, Opuntia).

$2{{C}_{6}}{{H}_{12}}{{O}_{6}}+3{{O}_{2}}\to 3{{C}_{4}}{{H}_{6}}{{O}_{5}}+3{{H}_{2}}O;\frac{C{{O}_{2}}}{{{O}_{2}}}=\frac{0}{3}=0$ (Zero)

(6) Respiration in the absence of O2 (in anaerobic respiration)

${{C}_{6}}{{H}_{12}}{{O}_{6}}\xrightarrow{\text{Zymase}}2{{C}_{2}}{{H}_{5}}OH+2C{{O}_{2}}$;

$\frac{C{{O}_{2}}}{{{O}_{2}}}=\frac{2}{0}=\infty$(Infinite)

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