Respiration

Question 1

4 Main stages in aerobic respiration and where they occur

Answer 1

Glycolysis: cytoplasm
Link reaction: mitochondrial matrix
Krebs cycle: mitochondrial matrix
Oxidative phosphorylation via electron transfer chain: membrane of cristae

Question 2

Outline the stages of glycolysis

Answer 2

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 & 2x ATP per glucose

Question 3

How does pyruvate from glycolysis enter the mitochondria?

Answer 3

Via active transport

Question 4

What happens during the link reaction?

Answer 4

1. Oxidation of pyruvate to acetate

Per pyruvate molecule: net gain of 1xCO2 (decarboxylation) & 2H atoms (used to reduce 1xNAD).

2. Acetate combines with coenzyme A (CoA) to form acetyl coenzyme A

Question 5

Give a summary equation for the link reaction

Answer 5

pyruvate + NAD + CoA
—->
Acetyl CoA + reduced NAD + CO2

Question 6

What happens in the Krebs cycle?

Answer 6

Series of redox reactions produces:

• ATP by substrate-level phosphorylation
• Reduced coenzymes
• CO2 from decarboxylation

Question 7

What is the electron transfer chain?

Answer 7

Series of carrier proteins embedded in membrane of the cristae of mitochondria

Produces ATP through oxidative phosphorylation via chemiosmosis during aerobic respiration

Electrons released from reduced NAD & 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 8

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

Answer 8

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

Question 9

How does chemiosmosis produce ATP during aerobic respiration?

Answer 9

H+ ions (protons) move down their concentration gradient from the inter membrane space into the mitochondrial matrix via the channel protein ATP synthase.

ATP synthase catalyse ADP + Pi —> ATP

Question 10

State the role of oxygen in aerobic respiration

Answer 10

Final electron acceptor in electron transfer chain

produces water as a byproduct

Question 11

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

Answer 11

• energy is released gradually

- less energy is released as heat

Question 12

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

Answer 12

• (amino acids from) proteins

- (glycerol and fatty acids from) lipids

Question 13

How can lipids act as an alternative respiratory substrate?

Answer 13

lipid –> glycerol + fatty acid

1. Phosphorylation of glycerol –> TP for glycolysis.
2. Fatty acid —> acetate
   a) acetate enters link reaction
   b) H atoms produced for oxidative phosphorylation

Question 14

How can amino acids act as an alternative respiratory substrate?

Answer 14

Deamination produces:

1. 3C compounds
2. 4C/5C compounds –> intermediates in Krebs cycle

Question 15

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

Answer 15

• Glycolysis (anaerobic)

- Krebs cycle (aerobic)

Question 16

What happens during anaerobic respiration in animals?

Answer 16

Only glycolysis continues

reduced NAD + pyruvate
—->
oxidised NAD (for further glycolysis + lactate

Question 17

What happens to the lactate produced in anaerobic respiration?

Answer 17

Transported to liver via bloodstream, where it is oxidised too pyruvate.

Can enter link reaction in liver cells or be converted to glycogen

Question 18

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

Answer 18

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 19

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

Answer 19

Converts reduced NAD back into NAD so glycolysis can continue.

Question 20

What is the disadvantage of producing ethanol during anaerobic respiration?

Answer 20

• Cells die when ethanol concentration is above 12%.

- Ethanol dissolves cell membranes

Question 21

What is the disadvantage of producing lactate during anaerobic respiration?

Answer 21

Acidic, so decreases pH.

Results in muscle fatigue.

Question 22

Compare aerobic and anaerobic respiration

Answer 22

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

Question 23

Contrast aerobic and anaerobic respiration

Answer 23

Aerobic:

• produces ATP by substrate-level phosphorylation and oxidative phosphorylation
• produces much more ATP
• does not produce ethanol or lactate

Anaerobic:

• substrate-level phosphorylation only
• produces fewer ATP
• produces ethanol or lactate

Question 24

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

Answer 24

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

Question 25

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

Answer 25

Absorbs CO2 so that there is a net decrease in pressure as O2 is consumed

Question 26

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

Answer 26

Volume of O2 produced or CO2 consumed/ time x mass of sample

Volume = distance moved by coloured drop x (0.5 x capillary tube diameter)2 x pi