5.7.13 Respiratory Quotient (RQ)

Question 1

What is the respiratory quotient?

Answer 1

The ratio of carbon dioxide molecules produced to oxygen molecules taken in during respiration

Question 2

State the equation for respiratory quotient

Answer 2

CO2 produced/O2 consumed

Question 3

Why do carbohydrates, lipids, and proteins have different typical RQ values?

Answer 3

Because the number of carbon-hydrogen bonds atoms differs in each type of biological molecule

Question 4

Why is a molecule with more hydrogen atoms more advantageous?

Answer 4

• More H atoms used to create a proton gradient
• More H means that more ATP molecules can be produced
• More O2 is therefore required to breakdown the molecule

Question 5

What is the RQ value when glucose is aerobically respired?

Answer 5

1 as equal amounts of carbon dioxide are produced to oxygen taken in

Question 6

What is the RQ of carbohydrates?

Answer 6

1.0

Question 7

What is the RQ of lipids?

Answer 7

0.7

Question 8

What is the RQ of proteins?

Answer 8

0.9

Question 9

Linoleic acid (fatty acid found in nuts) has the molecular formula C18H32O.
Calculate the RQ value for this molecule

Answer 9

C18H32O2 + O2 -> CO2 + H2O

C x 18 C x 1
H x 32 H x 2
O x 4 O x 3

C18H32O2 + 25O2 -> 18CO2 + 16H2O

CO2/O2 = RQ
18/25 =0.72 0.72

Question 10

What type of anaerobic respiration occurs in mammalian muscle cells?

Answer 10

Lactate fermentation

Question 11

What type of anaerobic respiration occurs in plant tissue cells?

Answer 11

Ethanol fermentation

Question 12

Why can RQ not be calculated for anaerobic respiration in muscle cells?

Answer 12

Becuase no oxygen is used and no carbon dioxide is produced during lactate fermentation

Question 13

Why does RQ tend to head toward infinity in yeast cells?

Answer 13

As no oxygen is used while carbon dioxide is still being produced

Question 14

How can a respirometer be used to calculate respiratory quotients?

Answer 14

The manometer fluid moves according to how much oxygen has been consumed and carbon dioxide produced

Question 15

Calculating RQ from a respirometer experiment where:
x = 2.9 cm3 min-1

and

y = 0.8 cm3 min-1

RQ = x-y/x

Answer 15

Substitue the relevant values into the equation:
RQ = 2.9-0.8/2.9
= 0.724

Question 16

What is indicated when an RQ value changes?

Answer 16

Means the susbtrate being respired has changed

Question 17

What does an RQ of 0.85 indicate?

Answer 17

Suggests that both carbohydrates and lipids are being used

Question 18

What can RQ also give an indication of?

Answer 18

Under or overfeeding
- RQ of more than 1 suggests excessive carb intake
- RQ of less than 0.7 suggests underfeeding