Topic 5.2 - Respiration

Question 1

Why is respiration important? (2)

Answer 1

• Respiration produces ATP (to release energy)
• For active transport, protein synthesis etc…

Question 2

Summarise the stages of aerobic respiration (4)

Answer 2

1) Glycolysis - cytoplasm

2) Link reaction - mitochondrial matrix

3) Krebs cycle - mitochondrial matrix

4) Oxidative phosphorylation - inner mitochondrial membrane

Question 3

Summarise the stages of anaerobic respiration (2)

Answer 3

1) Glycolysis - cytoplasm

2) NAD regeneration - cytoplasm

Question 4

Describe the process of glycolysis (3)

Answer 4

1) Glucose phosphorylated to glucose phosphate
- Using inorganic phosphates from 2 ATP

2) Hydrolysed to 2x triose phosphate

3) Oxidised to 2 pyruvate
- 2 NAD reduced
- 4 ATP regenerated (net gain of 2)

Question 5

Explain what happens after glycolysis if respiration is anaerobic (3)

Answer 5

1) Pyruvate converted to lactate or ethanol

2) Oxidising reduced NAD -> NAD regenerated

3) So glycolysis can continue allowing continued production of ATP

Question 6

Suggest why anaerobic respiration produces less ATP per molecule of glucose than aerobic respiration (2)

Answer 6

1) Only glycolysis involved which produces less ATP per molecule of glucose than aerobic respiration

2) No oxidative phosphorylation which forms majority of ATP

Question 7

What happens after glycolysis if respiration is aerobic?

Answer 7

Pyruvate is actively transported into the mitochondrial matrix

Question 8

Describe the link reaction (2)

Answer 8

1) Pyruvate oxidised to acetate
- CO2 produced
- Reduced NAD produced

2) Acetate combines with coenzyme A, forming Acetyl coenzyme A

Question 9

Describe the Krebs cycle (2)

Answer 9

1) Acetyl coenzyme A reacts with a 4C molecule
- Releasing coenzyme A
- Producing a 6C molecule that enters the Krebs cycle

2) In a series of oxidation-reduction reactions, the 4C molecule is regenerated and:
- 2x CO2 is lost
- Coenzymes NAD & FAD reduced

Question 10

Describe the process of oxidative phosphorylation (4)

Answer 10

1) Reduced NAD/FAD oxidised to release H atoms -> split into protons and electrons

2) Electrons transferred down electron transfer chain (by redox reactions)

3) Energy released by electrons used in the production of ATP from ADP + Pi
- Energy used by electron carriers to actively pump protons from matrix -> intermembrane space
- Protons diffuse into matrix down an electrochemical gradient, via ATP synthase
- Releasing energy to synthesis ATP from ADP + Pi

4) In matrix at end of ETC, oxygen is the final electron acceptor
- So protons, electrons and oxygen combine to form water

Question 11

Give examples of other respiratory substrates (2)

Answer 11

1) Fatty acids from hydrolysis of lipids -> converted to Acetyl Coenzyme A

2) Amino acids from hydrolysis of proteins -> converted to intermediates in Krebs cycle