6.2.4 Respiratory quotientOng Yee Sing

2017

Respiratory quotient呼吸商

• Within specific time, the ratio of the quantity of carbon produced to quantity of oxygen consumed is known as the respiratory quotient.

RQ = CO

2 released

O2 consumed

• Functions:• calculate the quantity of oxygen consumed and quantity of carbon dioxide

released by applying the RQ.

• represents the oxidation reaction of various kinds of food (or substrate).

• reflect the metabolic rate of an organism.

• The RQ of most animals at rest is in the range of 0.8 to 0.9.

• The human RQ is about 0.85.

Respiratory quotients for common food

Substrate Equation RQ

Glucose C6H12O6 + 6 O2 → 6 CO2+ 6 H2O 6 CO2

6 O2

= 1.0

Fats palmitic acid C16H32O2 + 23 O2 → 16 CO2 + 16 H2O

16 CO2

23 O2

= 0.696

Proteins albuminC72H112N18O22S + 77 O2 → 63 CO2 + 38 H2O + SO3 + 9 CO(NH2)2

63 CO2

77 O2

= 0.8

• The RQ of fats may vary depending on the type of fat.

• 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.

• It is necessary to view such data with caution. If a mixture of substrates is being used then the figure will be different from the above, e.g. an RQ of 0.8 could point to both protein and fat being used.

Type of substances is being metabolise

• The graph below on the left the different RQ values of a seed during different stages of germination.

• This graph suggests that the seed begins with carbohydrate as a metabolite, changes to fat/oil then returns to mainly using carbohydrate.

• Any RQ which is not of the numbers given suggests a substrate combination is being used.

RQ represents types of respiration

• RQ < 1 aerobic respiration

• RQ = 1 aerobic respiration

• RQ > 1 anaerobic respiration

• Low value of RQ (<1) indicates that • Aerobic respiration is being carried out;• Plants absorb CO2 to carry out photosynthesis; • Animals utilize carbon element to manufacture calcareous shell.

• High value of RQ (>1) indicates that • Anaerobic respiration is being carried out;• Conversion of carbohydrates into fats e.g. for hibernation• process of large quantity of food for storage

RQ represents types of respiration

• RQ < 1 aerobic respiration

• RQ = 1 aerobic respiration

• RQ > 1 anaerobic respiration

• Low value of RQ (<1) indicates that • Aerobic respiration is being carried out;• Plants absorb CO2 to carry out photosynthesis; • Animals utilize carbon element to manufacture

calcareous shell.

• High value of RQ (>1) indicates that • Anaerobic respiration is being carried out;• Conversion of carbohydrates into fats e.g. during

hibernation and during conversion process of large quantity of food for storage

Top and left: Calcareous protistand marine shells.Bottom: Hibernation.

Quiz

• Respiratory quotient, RQ, is calculated using the formula:

A. RQ = carbon dioxide produced ÷ oxygen used

B. RQ = carbon dioxide used ÷ oxygen produced

C. RQ = glucose used ÷ carbon dioxide produced