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 (ETC): 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 acetylcoenzyme 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 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.

Question 8

What happens in the ETC?

Answer 8

• Electron s 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 a final electron acceptor.

Question 9

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

Answer 9

• 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 tranfer 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 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 compunds –> pyruvate for link reaction.
2. 4C/5C compunds –> intermediates in Krebs Cycle.

Question 16

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

Answer 16

• Glycolysis (anaerobic)
• Krebs cycle (aerobic)

Question 17

What happens during anaerobic respiration in animals?

Answer 17

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

Question 18

What happens to the lactate produced in anaerobic respiration?

Answer 18

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

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 ethanal using reduced NAD to produce oxidised NAD for further glycolysis.

Question 20

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

Answer 20

Converts reduced NAD back into NAD so glycolysis can continue

Question 21

What is the disadvantage of producing ethanol during anaerobic respiration?

Answer 21

• 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 which results in muscle fatigue.

Question 22

Similarities between anaerobic and aerobic 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 ehtanol 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
2. Use a dye as a 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 producd or CO2 consumed/ time x mass sample
• Volume = distance moved by coloured drop x (0.5 x capillary tube diameter)2 x pie