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)
3. 2x TP is oxidised to 2x pyruvate
   Net gain of 2x reduced NAD & 2x ATP per glucose.

Question 3

Draw a flowchart to represent what happens during glycolysis.

Answer 3

check

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 acetylcoenzyme A.

Question 5

How does pyruvate from glycolysis enter the mitochondria?

Answer 5

via active transport

Question 6

Give a summary equation for the link reaction.

Answer 6

pyruvate + NAD + CoA
→
acetyl CoA + reduced NAD + CO2

Question 7

Outline the stages of the Krebs cycle.c

Answer 7

NB: the 6C compound is citrate

check picture

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

What is the electron transfer chain (ETC)?

Answer 8

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

Question 9

What happens in the electron transfer chain (ETC)?

Answer 9

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 10

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

Answer 10

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 10

How does chemiosmosis produce ATP during aerobic respiration?

Answer 10

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 11

State the role of oxygen in aerobic respiration.

Answer 11

Final electron acceptor in electron transfer chain.
(produces water as a byproduct)

Question 12

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

Answer 12

● energy is released gradually
● less energy is released as heat

Question 13

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

Answer 13

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

Question 14

How can lipids act as an alternative respiratory substrate?

Answer 14

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 15

How can amino acids act as an alternative respiratory substrate?

Answer 15

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

Question 16

What happens to the lactate produced in anaerobic respiration?

Answer 16

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

Question 17

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

Answer 17

● Glycolysis (anaerobic) ● Krebs cycle (aerobic)

Question 18

What happens during anaerobic respiration in animals?

Answer 18

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

check picture

Question 19

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

Answer 19

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 20

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

Answer 20

check

Question 21

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

Answer 21

Converts reduced NAD back into NAD so glycolysis can continue.

Question 22

What is the disadvantage of producing ethanol during anaerobic respiration?

Answer 22

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

Question 23

What is the disadvantage of producing lactate during anaerobic respiration?

Answer 23

Acidic, so decreases pH. Results in muscle fatigue.

Question 24

Compare aerobic and anaerobic respiration.

Answer 24

● Both involve glycolysis ● Both require NAD
● Both produce ATP

Question 25

Contrast aerobic and anaerobic respiration.

Answer 25

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
lactat

Question 26

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

Answer 26

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 27

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

Answer 27

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

Question 28

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

Answer 28

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