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 3x triose phosphate (TP)

3) 2x TP 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 1x CO2 (decarboxylation) & 2H atoms (to reduce 1x NAD)

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 reactions produces:
• ATP by substrate- level phosphorylation
• reduced coenzymes
• CO2 from decarboxylation.

Question 7

What is the electron transfer chain (ETC)?

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 electron transfer chain (ETC)?

Answer 8

• electrons released from reduced NAD & FAD undergo successive redox reactions
• energy released coupled to maintaining proton gradient or released as heat.
• oxygen acts as final electron acceptor

Question 9

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

Answer 9

• some energy released from ETC coupled to the active transport of H+ ions from mitochondrial matrix into intermembrane space

Question 10

How does chemiosmosis produce ATP during aerobic respiration?

Answer 10

• H+ ions (protons) move down their conc gradient from the intermembrane space into mitochondrial matrix via 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 released gradually
• less energy released as heat

Question 13

Name 2 types 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

3) acetate enters link reaction

4) H atoms produced for oxidative phosphorylation

Question 15

How can amino acids act as an alternative respiratory substrate ?

Answer 15

Deamination produces:

• 3C compounds —> pyruvate for link reaction
• 4C/5C compounds —> intermediate in krebs cycle .

Question 16

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

Answer 16

• glycolysis (anaerobic )
• krebs cycle (aerobic )

Question 17

What happens during anaerobic respiration in animals ?

Answer 17

• only glycolysis continues reduces BAR + 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’s 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 (yeasts and some plant cells)?

Answer 19

• only glycolysis continues.
• pyruvate is decarboxylated to form ethanal.
• ethanal reduced to ethanol using reduced NAD to produce oxidised NAD for further glycolysis .

Question 20

What’s an 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 22

What’s the disadvantage of producing lactate during anaerobic respiration?

Answer 22

• acidic , so decreases pH . results in muscle fatigue

Question 23

Compare aerobic and anaerobic respiration.

Answer 23

• both involve glycolysis.
• both require NAD
• both produce ATP

Question 24

Contrast aerobic and anaerobic respiration.

Answer 24

aerobic:
- produces ATP by substrate-level phosphorylation
- produces much more ATP
- doesn’t produce ethanol or lactate

anaerobic:
- substrate-level phosphorylation only
- produces fewer ATP
- produced ethanol or lactate

Question 25

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

Answer 25

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 26

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

Answer 26

- absorbs CO2 so there’s net decrease in pressure as O2 is consumed

Question 27

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

Answer 27

- vol of O2 produced or CO2 consumed/ time x mass of sample - vol = distance moved by coloured drop x (0.5 x capillary tube diameter)^2 x pi

Question 28

Explain how the conversion of pyruvate to lactate allows ATP to be continuously produced .

Answer 28

- in anaerobic respiration in animals, pyruvate reduced to lactate as gains hydrogens from NADH. - Thus, NADH oxidised into NAD. NAD formed in this reaction returns back to glycolysis, ensuring glycolysis continue and ATP can be produced.

Question 29

Describe the role of oxygen in aerobic respiration.

Answer 29

- protons produced in glycolysis and the krebs cycle combine with oxygen and electrons to form water. - as result, oxygen allows electron transfer chain to function. - due to essential role in ETC, oxygen referred to as final electron acceptor.

Question 30

In the last stage of aerobic respiration, describe the proton gradient across the inner membrane and how it’s maintained.

Answer 30

- there’s higher conc of protons in intermembrane space compared to matrix, which establishes a proton gradient across inner membrane . - maintain proton gradient, protons actively transported from the matrix to intermembrane space. - ensures always higher conc of protons in intermembrane space compared to matrix

Question 31

How is ATP produced in the final stage of aerobic respiration?

Answer 31

- enzyme ATP synthase used. - to catalyse the production ATP by this enzyme, energy supplied through the diffusion of protons down a proton gradient . As a result , these particles move from intermembrane space to matrix - movement of ions across partially permeable membrane, from area high concentration to area low conc - chemiosmosis

Question 32

Explain why more ATP is produced in aerobic respiration compared to anaerobic respiration?

Answer 32

- from a single molecule of glucose = overall yield of 2 ATP in anaerobic. —> produces ATP is glycolysis. - but in aerobic, ATP made in glycolysis, krebs cycle & oxidative phosphorylation. Single glucose molecule - possible over 30 ATP molecules made during OP.