18.6 Respiratory Substrates

Question 1

What are respiratory substrates?

Answer 1

organic molecules

broken down during respiration

Question 2

What apparatus is used to measure the respiratory quotient?

Answer 2

respirometer

Question 3

What is the formula for the respiratory quotient?

Answer 3

CO2 produced ÷ O2 consumed

Question 4

What are the respiratory quotients of different respiratory substrates?

Answer 4

carbohydrates = 1.0

proteins = 0.9

lipids = 0.7

Question 5

Why is the respiratory quotient of lipids less than that of carbohydrates?

Answer 5

lipids contain more C-H bonds

1 lipid molecule requires more O₂ to hydrolyse than 1 carbohydrate molecule

CO₂ produced < O₂ consumed

Question 6

Explain why a respiratory quotient may be above 1:

Answer 6

during anaerobic respiration, CO₂ is released without any O₂ being consumed

therefore arises due to mixture of aerobic & anaerobic respiration

Question 7

Outline the respiration pathway of a triglyceride:

Answer 7

broken down into fatty acids + glycerol

fatty acids undergo beta oxidation, forming acetyl groups

acetyl groups taken into Krebs cycle by coenzyme A

glycerol converted to pyruvate, which undergoes oxidative phosphorylation

Question 8

How does a respirometer work?

Answer 8

Contains potassium hydroxide solution + respiring tissue.

CO₂ released from respiration is absorbed by NaOH, decreasing volume of air within respirometer

fluid in graduated tube pulled down due to lower pressure