3.5.2 Respiration

Question 1

(Respiration) 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

(Respiration) Outline the stages of glycolysis. (3 + net gain)

Answer 2

1) Glucose is phosphorylated to glucose phosphate by 2x ATP.
2) Glucose phosphate splits into 2x triose phosphate.
3) 2x triose phosphate is oxidised to 2x pyruvate.
Net gain of 2x reduced NAD and 2x ATP per glucose.

Question 3

(Respiration) How does pyruvate from glycolysis enter the mitochondria?

Answer 3

Via active transport.

Question 4

(Respiration) 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

(Respiration) Give a summary equation for the links reaction.

Answer 5

pyruvate + NAD + CoA ➡️ acetyl CoA + reduced NAD + CO2

Question 6

(Respiration) 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

(Respiration) Outline the stages of the Krebs cycle.

Answer 7

1) 2C Acetyl CoA combines with a 4C organic compound to produce a 6C molecule.
2) The 6C molecule is oxidised, with H atoms transferred to form reduced NAD and it loses a carbon as CO2 forming a 5C molecule.
3) The 5C molecule is oxidised, with H atoms transferred to form reduced NAD and it loses a carbon as CO2 forming a 4C molecule.
4) The 4C molecule is further oxidised producing reduced NAD and reduced FAD. ATP is also formed.
5) The original 4C molecule that reacts with acetyl CoA is regenerated and the cycle continues.

Question 8

(Respiration) 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

(Respiration) 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

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

Answer 10

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

Question 11

(Respiration) How does chemiosmosis produce ATP during aerobic respiration?

Answer 11

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 12

(Respiration) State the role of oxygen in aerobic respiration.

Answer 12

Final electron acceptor in electron transfer chain.

(Produces water as a by-product).

Question 13

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

Answer 13

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

Question 14

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

Answer 14

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

Question 15

(Respiration) How can lipids act as an alternative respiratory substrate?

Answer 15

Lipid ➡️ glycerol + fatty acids
1) Phosphorylation of glycerol ➡️ TP for glycolysis
2) Fatty acid ➡️ acetate
a) Acetate enters link reactions
b) H atoms produced for oxidative phosphorylation

Question 16

(Respiration) How can amino acids act as an alternative respiratory substrate?

Answer 16

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

Question 17

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

Answer 17

• Glycolysis (anaerobic)
• Krebs cycle (aerobic)

Question 18

(Respiration) What happens during an aerobic respiration in animals?

Answer 18

Only glycolysis continues
Reduced NAD + pyruvate ➡️ oxidised NAD (for further glycolysis) + lactate

Question 19

(Respiration) What happens to the lactate produced in anaerobic respiration?

Answer 19

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

Question 20

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

Answer 20

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 21

(Respiration) 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

(Respiration) 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

(Respiration) What is the disadvantage of producing lactate during anaerobic respiration

Answer 23

• Acidic, so decreases pH
• Results in muscle fatigue

Question 24

(Respiration) Compare aerobic and anaerobic respiration (similarities).

Answer 24

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

Question 25

(Respiration) Contrast aerobic and anaerobic respiration (differences).

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 lactate

Question 26

(Respiration) 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 a 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

(Respiration) 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

(Respiration) 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