5.7: Respiration

Question 1

Why does aerobic respiration yield fewer molecules of ATP than the theoretical maximum? (2mks) [f214 june 15 q3aii]

Answer 1

1 some ATP used to (actively) transport pyruvate (into the mitochondrion) ;
2 some ATP used to (actively) transport H(+) from (reduced) NAD , formed in glycolysis / into the mitochondrion ;
3 some energy released in ETC , is not used to transport H+ (across inner membrane) / is released as heat ; [in context of oxidative phosphorylation]
4 not all the H+ movement (back across membrane) , is used to generate ATP / is through ATP synth(et)ase ; [ref to H+ leaking (back into matrix or out into cytoplasm) resulting in less ATP generated]
5 not all the, reduced NAD / red NAD / NADH , is used to feed into the ETC ; [use of (some of) the red NAD for other purpose]

Question 2

Explain why the incomplete breakdown of glucose in anaerobic respiration produces less ATP than aerobic respiration? (5mks) [f214 june 15 q3b]

Answer 2

in anaerobic respiration:
1 glycolysis/ conversion of glucose into pyruvate, occurs ;
2 produces 2 molecules of ATP (net) ;
3 (only) substrate level phosphorylation (occurs) ;
4 oxygen not available as final electron acceptor ; [oxygen is available as the final electron acceptor in aerobic]
5 pyruvate / ethanal , used to regenerate NAD for glycolysis (to continue) ; [pyruvate refers to lactate pathway, ethanal refers to fermentation]
6 (Krebs cycle and) electron transport chain/ chemiosmosis/ oxidative phosphorylation , do not occur ; [ETC (etc.) ONLY occur(s) in aerobic]

Question 3

The anaerobic respiration pathway in animal cells can be reversed, but the anaerobic respiration pathway in yeast cells cannot be reversed.
Explain why, using your knowledge of the differences between the two pathways. (4mks) [F214 June 14 q5bii]

Answer 3

in animals:
A1 pyruvate is , converted / reduced , to , lactate / lactic acid ;
A2 can be reversed as no , atoms lost / other product formed ; [e.g. pyruvate and lactate are both 3C compounds so reaction can be reversed]
A3 lactate dehydrogenase available to reverse the reaction ;
in yeast:
Y1 pyruvate converted to ethanol (in 2 steps) and
carbon dioxide / CO2 ; [pyruvate decarboxylated to ethanol]
Y2 cannot be reversed as , carbon dioxide is / atoms are , lost ; [e.g. pyruvate is 3C and , ethanol / ethanal , is 2C so reaction cannot be reversed]
Y3 (de)carboxylase enzyme cannot reverse the reaction ;

Question 4

State precisely where in the cell glycolysis occurs. [F214 June 13 q5ai]

Answer 4

cytoplasm (of cell) ; [cytosol]

Question 5

Outline the process of glycolysis. (4mks) [F214 June 13 q5aii]

Answer 5

1 phosphorylation of glucose ;
2 so forming hexose (1,6) bisphosphate ; [fructose(-1,6-)bisphosphate; hexose biphosphate]
3 (then) splitting into / formation of , two / 2 , triose phosphate(s) / TP ;
4 (for formation of pyruvate) dehydrogenation / oxidation / formation of reduced NAD ; [formation of , NADH2 / NADH (+H+) / red NAD]
5 pyruvate produced (from , TP / (3C) intermediate) ;
6 total production 4 ATP / net production of 2 ATP ;

Question 6

State precisely where in the liver cell the excess reduced NAD can be re-oxidised. [F214 Jan 13 2cii]

Answer 6

crista(e) / inner mitochondrial membrane ; [(at) electron transport chain]

Question 7

In the space below, indicate how these sub-units are joined in a molecule of ATP. (2mks) [F214 Jan 13 5ai]

Answer 7

row of 3 phosphates joined to ribose and
ribose joined to adenine ;
phosphates and adenine shown joined to correct place
on ribose or stated that phosphate(s) joined to carbon 5 and adenine joined to carbon 1 ;

Question 8

Suggest the type of reaction that removes a phosphate group from an ATP molecule. [F214 Jan 13 5aii]

Answer 8

hydrolysis; [dephosphorylation]

Question 9

Electron transfer occurs on the inner membrane of the

mitochondrion. [F214 Jan 13 5bi]

Answer 9

1 In isolated mitochondria that have had their outer membranes removed, electron transfer takes place but the mitochondria are unable to produce ATP.

Question 10

Protons accumulate in the inter-membrane space. [F214 Jan 13 5bi]

Answer 10

2 The pH of the inter-membrane space is lower than the pH inside the rest of the mitochondrion.
3 The outer mitochondrial membrane is permeable to protons. If isolated mitochondria are supplied with ADP and inorganic phosphate and placed in a solution of pH 8, no ATP is produced. If, however, these mitochondria are placed in an acidic solution, ATP is produced.

Question 11

State the precise location of the electron transport chain in the cell. [F214 June 12 3a]

Answer 11

crista(e) / inner mitochondrial membrane ; [thylakoid membrane / lamella(e) (of chloroplast)]

Question 12

One way of calculating the rate of respiration is to measure the volume of oxygen taken up over a period of time.
A student carried out an experiment to investigate the effect of temperature on the rate of respiration in soaked (germinating) pea seeds and dry (dormant) pea seeds.
A simple piece of apparatus called a respirometer was used, as shown in Fig. 4.1.
The potassium hydroxide solution in this apparatus absorbs carbon dioxide. If the apparatus is kept at a constant temperature, any changes in the volume of air in the respirometer will be due to oxygen uptake.
(a)State the stage or stages of aerobic respiration during which:
(i)carbon dioxide is produced (1mk)
[F214 Jan 12 4ai]

Answer 12

link reaction and Krebs cycle ;

Question 13

One way of calculating the rate of respiration is to measure the volume of oxygen taken up over a period of time.
A student carried out an experiment to investigate the effect of temperature on the rate of respiration in soaked (germinating) pea seeds and dry (dormant) pea seeds.
A simple piece of apparatus called a respirometer was used, as shown in Fig. 4.1.
The potassium hydroxide solution in this apparatus absorbs carbon dioxide. If the apparatus is kept at a constant temperature, any changes in the volume of air in the respirometer will be due to oxygen uptake.
(a)State the stage or stages of aerobic respiration during which:
(ii)oxygen is used. (1mk)
[F214 Jan 12 4aii]

Answer 13

oxidative phosphorylation ; [electron transport chain /

electron transport system / electron carrier chain]

Question 14

4b) The student set up three respirometers, A, B and C, in water baths at two different temperatures. The respirometers were left for 10 minutes in order to equilibrate.
The contents of each respirometer are shown in Table 4.1
temperature: 15C; respirometer A; 30 soaked pea seeds// respirometer B; glass beads + 30 dry pea seeds// respirometer C; glass beads

temperature: 25C; respirometer A; 30 soaked pea seeds// respirometer B; glass beads + 30 dry pea seeds// respirometer C; glass beads

At each temperature, respirometer C, which contained only glass beads, was a control.
Respirometer B, at each temperature, also contained some glass beads.
(i)Suggest why, at each temperature, respirometer B contained some glass beads. (2mks)
[F214 Jan 12 4bi]

Answer 14

1) to make the volume of , contents / ‘peas’ , the same
(in the respirometers) ;
2) idea that because the volume of peas in A is greater than the volume of peas in B
or the peas in A , are bigger / take up more space
or the peas in A have absorbed water
or the peas in B , are smaller / take up less space ; [must refer to A / soaked / germinating and/or B / dry / dormant]
3) as without the beads there would be more ,
air / gas / oxygen , in B than in A ; [idea that with the presence of beads the volume of gas would be the same]

Question 15

(ii)Suggest how the student determined the quantity of glass beads to place in respirometer B at each temperature. (2mks) [F214 Jan 12 4bii]

Answer 15

1 (determined by) finding difference in volume between
(30) soaked , seeds / peas and (30) dry , seeds / peas ;
2 the difference represents the volume of glass beads
required or add the quantity of glass beads necessary to make the volumes (of respirometer contents) equal ;
3 calculate / knowing , volume of 1 bead to determine
number of beads equivalent to volume required ; [ref to mass/weight instead of volume throughout
(ii) as an error carried forward (ecf);; any suitable method of determining the volume of beads required
e.g. ● displacement ● put soaked peas in tube and measure volume; mark; then put dry peas in and add
glass beads into tube and top up to mark]

Question 16

Explain why there is an increased rate of respiration in soaked seeds at 25°C compared with soaked seeds at 15°C. (2mks) [F214 Jan 12 4cii]

Answer 16

at, higher temperature / 250C increased kinetic energy ;
(named respiratory) enzymes / decarboxylases / dehydrogenases , involved ; [Needs a clear statement that they are involved in respiration]

Question 17

Suggest a reason for the difference in the rate of respiration between soaked and dry pea seeds. (2mks) [F214 Jan 12 4ciii]

Answer 17

1 reactions require aqueous medium / reactions need to take place in water / reactions need to take place in solution ; [‘germinating’ for ‘soaked’, ‘peas’ for ‘seeds’,
‘dormant’ for ‘dry’ throughout]
2 enzymes and substrates can move (to collide)
in soaked seeds or movement (of reactants) , prevented / limited , in dry seeds ;
3 soaked seeds need more , ATP / energy or dry seeds need less , ATP / energy ;
4 for , protein synthesis / mitosis / other (named) metabolic reaction; [soaked peas have increased metabolism]

Question 18

Organisms require energy in order to carry out essential metabolism. Organisms are able to
release energy by carrying out both aerobic and anaerobic respiration.
(a) Complete the table to compare anaerobic respiration in mammals // yeast. [F214 Jan 11 1a]
- name of hydrogen acceptor after glycolysis
- is CO2 produced?
- name of final product

Answer 18

pyruvate, pyruvic acid // ethanal/ acetaldehyde
no // yes (1 molecule) [2 molecules for yeast (from 1 glucose molecule)]
lactate/ lactic acid // ethanol

Question 19

Suggest one benefit of anaerobic respiration to an organism. [F214 Jan 11 1b]

Answer 19

ATP produced / energy released ;
recycles NAD / NAD can be used again ; [‘reoxidises red NAD’ (as implies recycling)]
allows , glycolysis / description of glycolysis , to take place / to continue ;

Question 20

Triose phosphate is a compound that is central to the metabolism of this cell.
Explain how the three reaction pathways (W, X and Y) are able to work independently of each other in the same leaf cell. [F214 Jan 11 3aii] (3mks)

Answer 20

1) take place in different , parts / organelles , of the cell
or compartmentalisation / reactions separated by membranes ;
2) W / glycolysis , in cytoplasm ; X / Calvin cycle , in , chloroplast / stroma (of chloroplast) ;
3) W / glycolysis , in , mitochondrion / matrix (of mitochondrion) ;
4) different enzymes for each pathway/ different conditions for each pathway;

Question 21

W / glycolysis;X / Calvin cycle; Y/ Krebs Cycle
Identify which of these three reaction pathways (W, X and Y) are associated with:
photosynthesis
aerobic respiration
[F214 Jan 11 3aiii]

Answer 21

X;

W Y;

Question 22

State the products of oxidative phosphorylation. (2mks) [F214 Jan 11 3aiv]

Answer 22

ATP / adenosine triphosphate ;
water / H2O ;
(oxidised) NAD / FAD ;

Question 23

Explain the role of coenzymes in this leaf cell, with respect to the metabolic reactions outlined in Fig. 3.1. [F214 Jan 11 3b] (3mks)

Answer 23

1) NAD / FAD / NADP , can , accept hydrogen / accept H / be reduced ;
2) reduced , NAD / FAD , supplies / carries , electrons ,
to the electron transport chain / for oxidative phosphorylation ;
3) reduced , NAD / FAD , supplies / carries , hydrogen ions for , chemiosmosis / oxidative phosphorylation ;
4) reduced NADP , supplies / carries , hydrogen to ,
light independent stage / Calvin cycle / X ;
5) coenzyme A / CoA , carries , acetate / ethanoate / acetyl group , to , Krebs cycle / Y ;
6) co-enzyme(s) / cytochrome(s) , transfer / accept and release , electrons along the electron transport chain/
can be , recycled / oxidised and reduced

Question 24

With reference to Fig. 1.1, describe and explain the role of ATP in the cell. [F214 June 10 1aii] (3mks)

Answer 24

1 transfers energy / energy ‘currency’ / releases energy / universal energy molecule / energy intermediate / (immediate) source of energy ;
2 phosphate(s) can be removed by hydrolysis ; [ATP → ADP + P(i) by hydrolysis or ATP + H2O → ADP + P(i) (must include water)]
3 to , release / provide , 30kJ (mol-1) energy ; [28 – 32 kJ]
4 (energy released for) metabolism / appropriate named reaction / appropriate reaction described; [e.g. muscle contraction// active transport// phosphorylation// glycolysis// during movement // binding to proteins to change their shape]
5 ADP can attach a phosphate (forming ATP) during ,
respiration / photosynthesis ; [during, oxidative phosphorylation /chemiosmosis /substrate level phosphorylation / photophosphorylation]
6 energy released in , small ‘packets’ (to prevent cell damage) / suitable quantity ;

Question 25

Some animals conserve energy by entering a state of torpor (a short period of dormancy), in which they allow their body temperature to fall below normal for a number of hours.
In an investigation into torpor in the Siberian hamster, Phodopus sungorus, the animal’s respiratory quotient (RQ) was measured before and during the period of torpor.
RQ = vol of CO2 produced/ vol of O2 consumed in the same time
RQ values for different respiratory substrates have been determined and are shown in Table 1.1.
substrate // RQ
carbohydrate // 1.0
lipid // 0.7
protein // 0.9
(i) Initially, the RQ value determined for the hamster was 0.95, but as the period of torpor progressed, its RQ value decreased to 0.75. What do these values suggest about the substrates being respired by the hamster during the period of the investigation?
[F214 June 10 1ci] (3mks)

Answer 25

1 SUBSTRATE respired changes over time ; [Needs to be a clear statement and not just names and not inferred from candidate’s complete answer]
2 initially respires (mostly) , glucose / carbohydrate ; [IGNORE respiring protein]
3 lower / decrease in / 0.75 , RQ indicates (more) ,
fat / lipid , as substrate or as time goes by (more) lipid is respired ; [IGNORE respiring protein]
4 glucose / carbohydrate , used up / decreases (over time) ;
5 protein not likely to be used as substrate / protein only used as a last resort ; [‘Less protein respired’ isn’t quite enough for this mp]

Question 26

Aerobic respiration may be summarised by the following equation:
C6H12O6 + 6O2 6CO2 + 6H2O
Although carbon dioxide and water are products of aerobic respiration, the equation is an
over-simplification of the process.
State and explain one way in which this equation is an over-simplification.
[F214 Jan 10 1b]

Answer 26

[‘fats can (also) be respired’ = E1
‘fats can be respired as well as glucose’ = S1 + E1]
S1) glucose is not the only substrate/ there are other substrates;
E1) named alternative substrate; or
S2) ATP is produced/ energy is released;
E2) (by) substrate level/ oxidative, phosphorylation; or
S3) ATP/ energy, required;
E3) (for) phosphorylation/ glycolysis; or
S4) is not a single step reaction/ other steps involved/
other products/ other intermediates;
E4) named stage(s)/ named intermediate compound(s); or [Krebs cycle/ ETC, happens = E4// ‘other stages such as link reaction are involved’ = S4 + E4 e.g. pyruvate/ acetyl CoA/ acetate IGNORE NAD(H) / FAD(H) / ATP]
S5) enzymes are involved;
E5) dehydrogenation/ decarboxylation/ oxidative phosphorylation/ named (respiratory) enzyme; or
S6) coenzymes/ NAD, involved;
E6) oxidative phosphorylation/ link reaction/ Krebs cycle/ glycolysis; or
S7) glucose does not, combine/ react, (directly) with oxygen;
E7) (oxygen) used in oxidative phosphorylation/
is final electron acceptor/ is final hydrogen acceptor;

Question 27

State precisely where in the cell glycolysis takes place.

[F214 Jan 10 2aii]

Answer 27

cytoplasm/ cytosol

Question 28

In anaerobic conditions, compound F (pyruvate) does not proceed to the link reaction.
Describe the fate of compound F (pyruvate) during anaerobic respiration in an animal cell and explain
the importance of this reaction. (5mks) [F214 Jan 10 2b]

Answer 28

1 (pyruvate / F) converted to, lactate/ lactic acid ;
2 F / pyruvate/ pyruvic acid, accepts hydrogen (atoms) ;
3 hydrogen from , reduced NAD / reduced E ; [NADH / NADH2 / NADH + H+]
4 (catalysed by), lactate dehydrogenase/ LDH ; [for pyruvate → lactate]
5 no, oxygen / O2 , to act as (final),
hydrogen / electron, acceptor ;
6 (so) link reaction / Krebs cycle / ETC, cannot take place ; [Needs a clear statement of not taking place // no , electron transport chain / electron carrier chain / chemiosmosis / oxidative phosphorylation]
7 NAD / E, regenerated / recycled / able to be re-used ; [IGNORE reduced NAD , oxidised / reoxidised
(as this does not give the idea of reusing it)]
8 allows glycolysis to continue / pyruvate continues to be made ;
9 limited / small amount of / some, ATP can be produced ; [1 ATP (per pyruvate) / 2 ATP (rather than
28-38 per glucose)/ only substrate level
phosphorylation]