Respiration

Question 1

Where does glycolysis occur?

Answer 1

cytoplasm

Question 2

Where does the link reaction occur?

Answer 2

mitochondrial matrix

Question 3

Where does the Krebs cycle occur?

Answer 3

mitochondrial matrix

Question 4

Where does oxidative phosphorylation occur?

Answer 4

via electron transfer chain: membrane of cristae

Question 5

Outline the stages of glycolysis.

Answer 5

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 6

How does pyruvate from glycolysis enter the mitochondria?

Answer 6

via active transport

Question 7

What happens during the link reaction?

Answer 7

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) & 2H atoms (used to reduce 1xNAD).

Question 8

Give a summary equation for the link reaction.

Answer 8

pyruvate + NAD + CoA→

acetyl CoA + reduced NAD + CO2

Question 9

What happens in the Krebs cycle?

Answer 9

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

Question 10

What is the electron transfer chain (ETC)?

Answer 10

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

Question 11

What happens in the electron transfer chain (ETC)?

Answer 11

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 12

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

Answer 12

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 13

How does chemiosmosis produce ATP during aerobic respiration?

Answer 13

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 14

State the role of oxygen in aerobic respiration.

Answer 14

Final electron acceptor in electron transfer chain.

produces water as a byproduct

Question 15

What is the benefit of an electron transfer chain

rather than a single reaction?

Answer 15

● energy is released gradually

● less energy is released as heat

Question 16

Name 2 types of molecule that can be used as

alternative respiratory substrates.

Answer 16

● (amino acids from) proteins

● (glycerol and fatty acids from) lipids

Question 17

How can lipids act as an alternative respiratory

substrate?

Answer 17

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 18

How can amino acids act as an alternative respiratory substrate?

Answer 18

Deamination produces:

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

Question 19

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

Answer 19

● Glycolysis (anaerobic)

● Krebs cycle (aerobic)

Question 20

What happens during anaerobic respiration in animals?

Answer 20

Only glycolysis continues

reduced NAD + pyruvate→ oxidised NAD (for further glycolysis) + lactate

Question 21

What happens to the lactate produced in anaerobic respiration?

Answer 21

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

Question 22

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

Answer 22

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 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
● 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 28

Suggest 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 cause 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 π