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 and 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) and 2H atoms (used to reduce 1xNAD)

2. acetate combines with coenzymes A (CoA) to form acetylcoenzyme A

Question 5

give a summary equation for the link reaction

Answer 5

pyruvate + NAD + CoA –> acetyl CoA + NADH + 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

Answer 7

series of carrier proteins embedded in membrane of the cristae of mitochondria

produces ATP thrpugh oxidative phosphorylation via chemiosmosis during aerobic respiration

Question 8

what happens in the electron transfer chain

Answer 8

electrons released from reduced NAD and FAD undergo successive redox reactions

energy released is coupled to maintaining proton gradient or released as heat

oxygen acts as 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 from the mitochondrial matrix into the intermembrane space

Question 10

how does chemiosmosis produce ATP during aerobic respiration

Answer 10

H+ ions 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 molecules 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

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 NAP + 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 ethanol using reduced NAD to produce oxidised NAD for further glycolysis

Question 20

what is the advantages 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 is 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: phosphorylation

Answer 24

aerobic produces ATP by substrate-level phosphorylation AND oxidative phosphorylation

anaerobic produces ATP by substrate-level phosphorylation only

Question 25

contrast aerobic and anaerobic respiration: amount of ATP

Answer 25

aerobic produces much more ATP than anaerobic

Question 26

contrast aerobic and anaerobic respiration: ethanol and lactate

Answer 26

aerobic respiration does not produce ethanol or lactate

anaerobic produces both

Question 27

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

Answer 27

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 28

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

Answer 28

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