5.2 Respiration

Question 1

Name the 4 main stages in aerobic respiration

Answer 1

1. Glycolysis
2. Link reaction
3. Krebs cycle
4. Oxidative phosphorylation

Question 2

Where does glycolysis occur?

Answer 2

Cell cytoplasm

Question 3

Where does the link reaction occur?

Answer 3

Mitochondrial matrix

Question 4

Where does the Krebs cycle occur?

Answer 4

Mitochondrial matrix

Question 5

Where does oxidative phosphorylation occur?

Answer 5

Via electron transfer chain, in the inner mitochondrial membrane (cristae)

Question 6

Outline the stages of glycolysis

Answer 6

1. Glucose is phosphorylated to glucose phosphate by 2x ATP
2. Glucose phosphate splits into 2x triose phosphate (TP)
3. 2x TP is oxidised to 2x pyruvate

Net gain of 2x reduced NAD and 2x ATP per glucose

Question 7

How does pyruvate from glycolysis enter the mitochondria?

Answer 7

Via active transport

Question 8

What happens during the link reaction?

Answer 8

1. Oxidation of pyruvate to acetate
   Per pyruvate molecule: net gain of 1x CO2 (decarboxylation) and 2H atoms (used to reduce 1x NAD)
2. Acetate combines with coenzyme A (CoA) to form acetylcoenzyme A

Question 9

Give a summary equation for the link reaction

Answer 9

Pyruvate + NAD + CoA —> acetyl CoA + reduced NAD + CO2

Question 10

What happens in the Krebs cycle?

Answer 10

Series of redox reactions produces:
- ATP by substrate-level-phosphorylation
- Reduced coenzymes
- CO2 from decarboxylation

Question 11

what is the electron transfer chain?

Answer 11

Series of carrier proteins embedded in membrane of the cristae of mitochondria
Produces ATP through oxidative phosphorylation via Chemiosmosis during aerobic respiration

Question 12

What happens in the electron transfer chain?

Answer 12

Electrons released from reduced NAD and FAD undergo successive redox reactions
The energy released is coupled to maintaining proton gradient or released as heat
Oxygen acts as final electron acceptor

Question 13

How is proton concentration gradient established during chemiosmosis in aerobic respiration?

Answer 13

Some energy released from the ETC is coupled to the active transport of H+ ions from the mitochondrial matrix into the inter membrane space

Question 14

How does chemiosmosis produce ATP during aerobic respiration?

Answer 14

Protons move down their concentration gradient from the inter membrane space into the mitochondrial matrix via the channel protein ATP synthase
ATP synthase catalyses ADP + Pi —> ATP

Question 15

State the role of oxygen in aerobic respiration

Answer 15

Final electron acceptor in electron transfer chain

Question 16

What is the benefit of an electron transfer chain rather than a single reaction?

Answer 16

• Energy is released gradually
• Less energy is released as heat

Question 17

Name 2 types of molecule that can be used as alternative respiratory substrates

Answer 17

• (amino acids from) proteins
• (glycerol and fatty acids from) lipids

Question 18

How can lipids act as an alternative respiratory substrate?

Answer 18

Lipid —> glycerol + fatty acids
1. Phosphorylation of glycerol —> TP for glycolysis
2. Fatty acid —> acetate
acetate enters link reaction
H atoms produced for oxidative phosphorylation

Question 19

How can amino acids act as an alternative respiratory substrate?

Answer 19

Deamination produces:
1. 3C compounds –> pyruvate for link reaction
2. 4C / 5C compounds –> intermediates in Krebs cycle

Question 20

Name the stages in respiration that produce ATP by substrate-level phosphorylation

Answer 20

Glycolysis (anaerobic)
Krebs cycle (aerobic)

Question 21

What happens during anaerobic respiration in animals?

Answer 21

Only glycolysis continues
reduced NAD + pyruvate –> oxidised NAD + lactate

Question 22

What happens to the lactate produced in anaerobic respiration?

Answer 22

Transported to liver via bloodstream, where it is oxidised to pyruvate
Can enter link reaction in liver cells or be converted to glycogen

Question 23

What happens during anaerobic respiration in some microorganisms e.g. yeast and some plant cells?

Answer 23

Only glycolysis continues
Pyruvate is decarboxylated to form ethanal
Ethanal is reduced to ethanol using reduced NAD to produce oxidised NAD for further glycolysis

Question 24

What is the advantage of producing ethanol / lactate during anaerobic respiration?

Answer 24

Converts reduced NAD back into NAD so glycolysis can continue

Question 25

What is the disadvantage of producing ethanol during anaerobic respiration?

Answer 25

• Cells die when ethanol concentration is above 12%
• Ethanol dissolves cell membranes

Question 26

What is the disadvantage of producing lactate during anaerobic respiration?

Answer 26

Acidic, so decreases pH
Results in muscle fatigue

Question 27

Compare aerobic and anaerobic respiration

Answer 27

• Both involve glycolysis
• Both require NAD
• Both produce ATP

Question 28

Contrast aerobic and anaerobic respiration

Answer 28

Aerobic:
- Produces ATP by substrate-level phosphorylation and oxidative phosphorylation
- Produces much more ATP
- does not produce ethanol or lactate

Anaerobic:
- Substrate-level phosphorlyation only
- Produces fewer ATP
- Produces ethanol or lactate

Question 29

Suggest how a student could investigate the effect of a named variable on the rate of respiration of a single-celled organism

Answer 29

1. Use respirometer (pressure changes in boiling tube causes a drop of coloured liquid to move)
2. Use a dye as the terminal electron acceptor for the ETC

Question 30

What is the purpose of sodium hydroxide solution in a respirometer set up to measure the rate of aerobic respiration?

Answer 30

Absorbs carbon dioxide so that there is a net decreases in pressure as oxygen is consumed

Question 31

How could a student calculate the rate of respiration using a respirometer?

Answer 31

Volume of oxygen produced or carbon dioxide consumed / time x mass of sample
Volume = distance moved by coloured drop x (0.5 x capillary tube diamater)^2 x pie