Module 5- Respiration

Question 1

2 marks

Describe how acetylcoenzyme A is formed in the link reaction

Answer 1

1. Oxidation of pyruvate and CO2 released
2. Addition of coenzyme A

Question 2

Give ways in which the properties of ATP make it a suitbale source of energy in biological processes

Answer 2

• Immediate source of energy
• Soluble
• Involves in a simple reaction
• Energy released in small amounts

Question 3

2 marks

Explain why it is necessary for humans to synthesise a large amount of ATP

Answer 3

• Immediate source of energy
• ATP only releases a small amount of energy at a time

Question 4

3 marks

Describe the part played by the inner membrane of a mitochondrion in producing ATP

Answer 4

• Electrons transferred down electron transport chain
• Electrons transfer energy to proteins which actively trasnport protons from matrix to intermemembrane space
• Protons diffuse down proton gradient and back into matrix via ATP synthase
• Energy used to combine ADP + Pi to produce ATP

Question 5

6 marks

Describe how ATP is made in mitochondria

Answer 5

1. Substrate level phosphorylation
2. Krebs cycle produces reduced coenzyme- reduced NAD and reduced FAD
3. Electrons released from reduced coenzymes
4. Electrons pass along electron transport chain
5. Energy released
6. ADP+Pi –> ATP
7. Protons move to intermembrane space via ATP synthase

Question 6

5 marks

Explain why it is important for plants to produce ATP during respiration in addition to during photosynthesis

Answer 6

1. In the dark no ATP production in photosynthesis
2. Some tissues unable to photosynthesise —> produce ATP
3. ATP cannot be stored
4. Plants uses more ATP than produced in photosynthesis
5. ATP for active transport

Question 7

4 marks

Describe process of glycolysis

Answer 7

1. Glucose is phosphorylated using Pi from ATP
2. NAD is reduced
3. As TP is oxidised to form pyruvate
4. Net gain of 2 ATP molecules- 4 ATP molecules are produced

Question 8

2 marks

Malonate inhibits the Krebs cycles
Explain why malonate would decrease the uptake of oxygen in a respiring cell

Answer 8

1. Less reduced NAD and reduced FAD made
2. Less oxidative phosphorylation
3. Less oxygen is used as a final electron acceptor

Question 9

2 marks

At the end of a sprint race, a runner continues to breathe rapidly for some time. Explain the advantage of this.

Answer 9

1. Lactate has built up
2. Oxygen used to break down lactate to pyruvate

Question 10

2 marks

Mitochondria in muscle cells have more cristae than mitochondria in skin cells. Explain the advantage of mitochondria in muscle cells having more cristae.

Answer 10

• More cristae = larger surface area for electron transport chain –> more enzymes for ATP production / oxidative phosphorylation
• Muscle cells use more ATP than skin cells

Question 11

6 marks

Oxidative phosphorylation

Answer 11

• Reduced NAD and reduced FAD are oxidised, and they donate elctrons to membrane protein
• This forms protons, NAD and FAD
• Electrons move along along membrane proteins through a series of redox reaction along ETC
• Electrons transfer energy to the proteins, which is used to actively trasnport protons from the matrix to intermembrane space
• Ptrotons in intermebrane space diffuse down proton gradient and back into matrix via ATP synthase
• ADP+Pi–> ATP, catalysed by ATP synthase/ ATPase
• Oxygen is final electron acceptor
• Over 30 ATP molecules can be made

Question 12

Explain glycolysis

Answer 12

1. Glucose is phosphorylated using Pi from ATP
2. NAD is reduced
3. As TP is oxidised to form pyruvate
4. Net product of 2 ATP & 4 ATP produced

Question 13

Anaerobic respiration in plants/yeasts and animals

Answer 13

Plants/ yeast: pyruvate–> ethanol +CO2—> ethanol
Animals: pyruvate–> lactic acid
Reduced NAD is oxidised

Question 14

Anaerobic respiration ATP production

Answer 14

1. Only ATP produced comes from glycolysis
2. The oxidised NAD can be used in glycolysis again

Question 15

Explain link reaction

Answer 15

1. Pyruvate enters mitochondrial matrix by active transport
2. Pyruvate oxidised to acetate
3. Acetate + coenzyme A–> acetlycoenzyme A

Question 16

Explain Krebs cycle

Answer 16

1. Acetlycoenzyme A + 4C–> 6C + coenzyme A
2. Series of redox reactions= coenzymes (to be used in oxidtive phosphorylation)
3. Carbon dioxide is released
4. ATP generated by substrate level phosphorylation
5. Other respiratory substrates- aa+ lipid breakdown products can fuel krebs cycle
6. Products from one glucose: 2 ATP, 6 reduced NAD, 6 reduced FAD, 6 CO2

Question 17

Explain oxidative phosphorylation

Answer 17

1. Electrons donated from coenzymes
2. e- transferred down ETC- releasing energy- series of redox reactions
3. Protons (H+) pumped across inner mitochondrial membrane
4. Conc gradient of H+ established- H+ diffuse through ATP synthase
5. ADP + Pi–> ATP (chemisosmotic theory)
6. Oxygen is the final electon acceptor–> H2O is formed

Question 17

6 marks

Describe how ATP is made in the mitchondria

Answer 17

1. Substrate level phosphorylation in the Krebs cycle
2. Krebs cycle produces reduced coenzymes e.g. reduced FAD and reduced NAD
3. Electrons released from FADH and NADH
4. Electrons pass along ETC, through a series of redox reactions
5. Energy is released
6. ADP+Pi—> ATP
7. Protons move into intermembrane soace
8. ATP synthase

Question 18

5 marks

The concentration of carbon dioxide in the air at different heights above ground in a forest changes over a period of 24 hours. Use your knowledge of photosynthesis to describe these changes and explain why they occur.

Answer 18

1. High concentration of carbon dioxide at night as no photosynthesis is occurring as light required for light-dependent reaction.
2. In the dark plants still respire.
3. In the light uptake of carbon dioxide is greater than carbon dioxide produced.
4. Decrease in carbon dioxide concentration with light
5. Increase in carbon dioxide concentration closer to ground as at ground level less photosynthesising due to less light.