5.2 Respiration

Question 1

Name the 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)
2. 2X TP is oxidised into 2X pyruvate

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

Question 3

Draw a flowchart to represent what happens during glycolysis

Question 4

How does pyruvate from glycolysis enter the mitochondria

Answer 4

Via active transport

Question 5

What happens during the link reaction

Answer 5

1.Oxidation of pyruvate to acetate

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

Per pyruvate molecule: net gain of 1XCO2(decarboxylation) and 2H atoms (used to reduce 1xNAD)

Question 6

Give a summary equation for the link reaction

Answer 6

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

Question 7

What happens in the Krebs cycle?

Answer 7

Series of redox reactions produces:

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

Question 8

Outline the stages of the Krebs cycle

Question 9

What is the electron transfer chain (ETC)?

Answer 9

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

Produces ATP through oxidative phosphorylation via chemiosmosis during aerobic respiration

Question 10

What happens in the electron transfer chain (ETC)?

Answer 10

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 11

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

Answer 11

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

Question 12

How does chemiosmosis produce ATP during aerobic respiration?

Answer 12

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

ATP synthase catalyses ADP + Pi —> ATP

Question 13

State the role of oxygen in aerobic respiration

Answer 13

Final electron acceptor in electron transfer chain. (Water produced as a byproduct)

Question 14

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

Answer 14

• energy is released gradually
• less energy is released as heat

Question 15

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

Answer 15

(Amino acids from) proteins
(Glycerol and fatty acids from) lipids

Question 16

How can lipids act as an alternative respiratory substrate?

Answer 16

Lipid—> glycerol + fatty acids

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

Question 17

How can amino acids act as an alternative respiratory substrate?

Answer 17

Deamination produces:

1. 3C compounds —> pyruvate for link reaction
2. 4C/5C compounds —> intermediates in Krebs cycle

Question 18

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

Answer 18

Glycolysis (anaerobic)
Krebs cycle (aerobic)

Question 19

What happens during anaerobic respiration in animals?

Answer 19

Only glycolysis continues

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

Question 20

What happens to the lactate produced in anaerobic respiration?

Answer 20

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

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

Question 21

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

Answer 21

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 22

Draw a flowchart to show how ethanol is produced during anaerobic respiration

Question 23

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

Answer 23

Converts reduced NAD back into NAD so glycolysis can continue

Question 24

What is the disadvantage of producing ethanol during anaerobic respiration?

Answer 24

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

Question 25

What is the disadvantage of producing lactate during anaerobic respiration?

Answer 25

Acidic, so decreases pH

Results in muscle fatigue

Question 26

Compare aerobic and anaerobic respiration

Answer 26

Both involve glycolysis
Both require NAD
Both produce ATP

Question 27

Contrast aerobic and anaerobic respiration

Answer 27

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

Anaerobic respiration
-substrate-level phosphorylation only
-produces fewer ATP
-produces ethanol or lactate

Question 28

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

Answer 28

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 29

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

Answer 29

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

Question 30

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

Answer 30

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