1. Practice Questions
Carbon monoxide inhibits the final electron carrier in the electron transport chain.
Explain how this affects ATP production via the electron transport chain (2)
Explain how this affects ATP production via the Krebs cycle

2. Answers
(a) the transfer of electrons down the electron transport chain stops (1 mark). There is no energy released to phosphorylate ADP/produce ATP (1 mark)
(b) the Krebs cycle stops (1 mark) because there is no oxidised FAD/NAD coming from the electron transport chain (1 mark)
(remember that when the electron transport chain is inhibited, the reactions that depend on the products of the chain are also affected)

3. The yield of ATP from respiration
Learning objectives:
(m) explain why the theoretical maximum yield of ATP per molecule of glucose is rarely, if ever, achieved in aerobic respiration
(o) define the term respiratory substrate;
(p) explain the difference in relative energy values of carbohydrate, lipid and protein respiratory substrates;

4. Continual production of ATP
The majority of ATP is synthesised via oxidative phosphorylation using the electron transport chain and chemiosmosis.
The cristae (folded inner membrane) of the mitochondria contain “stalked particles” which are the proteins where ATP synthase is found.
These molecules have a head and tail region.
tail
head

5. Continual production of ATP
ADP is phosphorylated to ATP. Oxygen is needed as the terminal acceptor for the protons and electrons that flow through the system.
The presence of oxygen means that ATP can be replaced as it is used.

6. 32 ATP can be made from 1 glucose molecule
Stages of respiration
Molecules produced
Number of ATP molecules
Glycolysis
2 ATP 2
2 reduced NAD
2 x 2.5 = 5
Link reaction (x2)
Krebs cycle (x2)
6 reduced NAD
6 x 2.5 = 15
2 reduced FAD
2 x 1.5 = 3
Total ATP = 32
2.5 ATP are made from each reduced NAD
1.5 ATP are made from each reduced FAD

7. Continual production of ATP
The number of ATP produced during aerobic respiration varies depending upon the physiological and biochemical conditions on the cells releasing the energy.
Up to 34 molecules of ATP can be released
This is based on conditions of pH7 with excess substrate – optimum conditions rarely found in cells.

8. Using other substrates to make ATP
Lipids (fats) and proteins can be used to generate ATP
Fat in the form of triglycerides can be broken down to glycerol and fatty acids
Fatty acids can be further broken down to 2C acetyl, which then combines with CoA to form acetyl CoA
The potential to generate ATP from lipids is much higher than of glucose e.g. 1 steric acid molecule can yield 146 molecules of ATP

9. Using other substrates to make ATP
Proteins cannot be stored in the body – they must be broken down by deamination in the liver.
Deamination splits the protein into amino acids.
Amino groups can enter the ornithine cycle and be incorporated into urea and an organic acid molecule that enters the Krebs cycle and so produces energy.
The ATP yield from amino acids is much less than of both glucose and lipids.

10. Task Work through questions 1-5 on page 143 of your textbook
These questions require a bit of “thinking outside the box” but you can do them 