Question

What is respiratory quotient? Explain...

Answer 1

Hello Dear !
______________________________________________________________It is the ratio of volume of carbon dioxide liberated in respiration to the volume of  oxygen consumed in it over a specific period of time by a unit tissue , organ or organisms , i.e., 
Respiratory quotient (R.Q.) = Volume of CO2  / Volume of O2 
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Respiratory quotient can be unity , less than one , zero and infinity .
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1.R Q equal to unity = It occurs during aerobic  respiration using carbohydrates as respiratory substrates .

C₆H₁₂O₆ + 6O₂ ----------> 6CO₂ + 6H₂O , R Q  = 6CO₂/6H₂O =1 or unity 

2. R Q less than One = Respiratory quotient is less than one in aerobic respiration  of fats and proteins .It is best observed during germination of fatty acids , e.g., Castor seed , Rape seed .

C₅₇H₁₀₄O₆ + 80 O₂ --------------> 57 CO₂ + 52 H₂O , RQ = 57 CO₂/80 O₂ = 0.71

3. RQ more than One = is more than one in aerobic respiration uses organic acids as respiratory substrates . 

2C₂H₅O₄ + O₂ ------------> 4CO₂ + 2H₂O , R Q = 4CO₂/ 1 O₂ = 4 

4.  RQ is infinity . It is recorded in case of anaerobic respiration where CO2 is evolved but O2 is not consumed , e.g., Alcoholic fermentation 

C₆H₁₂O₆n----------> C₂H₅OH + 2CO₂ , RQ = 2CO₂/0 = infinity or∞

5. RQ is zero = It is found in that case where oxygen is consumed but CO₂ is not evolved . This happens in case of succulent plants (e.g., Optunia) . All the CO₂ produced during respiration is fixed internally for use in photosynthetic activity during the day 
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Answer 2

hello frnd,
Definition

The respiratory quotient (RQ) is the ratio of CO2 produced to O2 consumed while food is being metabolized:

RQ = CO2 eliminated/O2 consumed

Most energy sources are food containing carbon, hydrogen, and oxygen. Examples include fat, carbohydrates, protein, and ethanol. Their metabolism is represented by the equation:

CxHyOz + (x + y/4 – z/2) O2 → x CO2 + (y/2) H2O

The normal range of respiratory coefficients for organisms in metabolic balance usually ranges from 1.0 – 0.7 and examples are calculated below:

Carbohydrates: The respiratory quotient for carbohydrate metabolism can be demonstrated by the chemical equation for oxidation of glucose:

C6H12O6 + 6 O2 → 6 CO2+ 6 H2O

Because the gas exchange in this reaction is equal, the respiratory quotient for carbohydrates is: RQ = 6 CO2 / 6 O2= 1.0

Fats: The chemical composition of fats differs from that of carbohydrates in that fats contain considerably fewer oxygen atoms in proportion to atoms of carbon and hydrogen. The substrate utilization of palmitic acid is:

C16H32O2 + 23 O2 → 16 CO2 + 16 H2O

Thus, the RQ for palmitic acid is approximately 0.7. RQ = 16 CO2 / 23 O2 = 0.696

Proteins: The respiratory quotient for protein metabolism can be demonstrated by the chemical equation for oxidation of albumin:

C72H112N18O22S + 77 O2 → 63 CO2 + 38 H2O + SO3 + 9 CO(NH2)2

The RQ for protein is approximately 0.8. RQ = 63 CO2/ 77O2= 0.8

Due to the complexity of the various ways in which different amino acids can be metabolized, no single RQ can be assigned to the oxidation of protein in the diet; however, 0.8 is a frequently utilized estimate.