1.
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2.
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3.
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4.
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5. The two diagrams below show nicotinamide adenine dinucleotide (NAD) and flavin adenine
dinucleotide (FAD), two nucleotides used in respiration.
(a) State two chemical features which these two molecules have in common and one difference
between the two molecules.
[3]
Features in common.
(i) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
..................
(ii) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
...................
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Difference
(b) Substrate level phosphorylation (SLP) is the simplest, oldest and least-evolved way to make
ATP. In substrate level phosphorylation, ATP is made during the conversion of an organic
molecule from one form to another. Energy released during the conversion is used to synthesise
the high energy bond of ATP.
(i) Describe the position of the 'high energy bond of ATP' referred to in the paragraph above.
[1]
(ii) Suggest why SLP is referred to as the 'simplest and oldest way to make ATP'.
[2]
The diagram below shows glycolysis, the link reaction and Kreb's cycle.
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(iii) Draw two arrows labelled A and B on the diagram opposite to show the two steps where
there is conversion of an organic molecule from one form to another and SLP occurs.
[2]
(iv) Give the number of ATP molecules made by SLP at each of the conversions shown in part
(iii) per glucose molecule in aerobic respiration.
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[2]
(c) (i) Where does the link reaction occur in cells?
[1]
(ii) Name the two types of enzyme involved in the link reaction.
[1]
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6. (a) Skeletal muscle fibres can respire aerobically and anaerobically.
(i) State precisely where in a muscle fibre aerobic respiration and anaerobic respiration take
place.
[1]
Aerobic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
...................
Anaerobic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
...................
(ii) State when a muscle fibre would respire anaerobically.
[1]
(b) (i) Describe the process by which lactic acid (lactate) is produced in muscle fibres.
[4]
(ii) Suggest why the lactic acid is removed from the muscle fibre.
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[1]
(c) What is meant by the term 'oxygen debt'?
[1]
(d) Other organisms can respire anaerobically. What are the terms used to describe the
following?
[2]
I. bacteria which only survive in the absence of oxygen
II. bacteria which grow in the presence or absence of oxygen
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7.
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8.
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9. The detailed diagram below shows the link reaction and Krebs cycle. Most of the intermediates
involved are named.
(a) (i) Using the diagram above, and your own knowledge, determine how many carbons there
are in the following Krebs cycle intermediates.
[1]
citrate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
......
α-ketoglutarate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.............
succinate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
........
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(ii) Explain precisely how you have arrived at these figures.
[2]
(b) Briefly describe how reduced FAD and reduced NAD are used to create an electrochemical
gradient.
[4]
In patients with a suspected mitochondrial disorder a minimally invasive tissue biopsy provides the
best opportunity to examine mitochondrial function, freezing the sample immediately after
collection. In addition to activity measurements of individual enzymes, analysis of mitochondrial
respiration and ATP production rates are performed. This includes the measurement of
mitochondrial oxygen consumption in the presence of different substrates, such as pyruvate and
α-ketoglutarate. Analysis may show increased levels of a Krebs cycle intermediate, such as
malate and succinate.
Defects in mitochondrial ATP synthesis may lead to high lactate levels in blood.
J Inherit Metab Dis. 2011 April; 34(2): 283-292
(c) Name the two enzyme types involved in the conversion of pyruvate to acetyl CoA
[2]
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Using the diagram opposite, the text above and your own knowledge, answer the following
questions.
(d) Suggest a suitable tissue to examine mitochondrial function and explain why you have chosen
this tissue with respect to patient safety.
[2]
(e) What could be deduced if the oxygen consumption was low with the pyruvate as a substrate
but high with α-ketoglutarate as a substrate?
[2]
(f) What could be deduced if there was a build up of any one of the Krebs cycle intermediates?
[1]
(g) Explain why there is a raised blood lactate level in many patients with mitochondrial disease.
[2]
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10.
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11. The diagram below shows the link reaction and the Krebs Cycle.
The number of carbon atoms present in some of the molecules is shown.
(a) State precisely where in the cell the reactions of the Krebs Cycle take place.
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[2]
(b) (i) On the diagram opposite, use arrows marked CO² to show the points where carbon
dioxide is removed.
[2]
(ii) Name the process by which the carbon dioxide is removed.
[1]
(iii) Describe briefly what happens to a molecule of carbon dioxide removed in this way in a
human.
[3]
(c) The role of the Krebs Cycle and glycolysis is to generate reduced NAD to be used in ATP
manufacture.
Describe the way in which reduced NAD is produced in the Krebs Cycle.
[3]
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(d) Reduced NAD is also produced during glycolysis.
Explain what happens to the reduced NAD under anaerobic conditions and why this is essential
for glycolysis to continue.
[2]
12. For each stage of the respiratory cycle shown in the table below use ticks (√) to indicate which
statements are correct.
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13. Respiration results in the production of ATP in cells. Production of ATP in the mitochondrion is
catalysed by an enzyme and requires energy supplied by a proton gradient. The diagram below
represents a model of the ATP synthetase complex.
(a) (i) On the diagram above, complete the equation for the production of ATP.
[1]
(ii) Name parts W and Z shown on the diagram above.
[2]
W ........................................................................... Z
...........................................................................
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(b) The proton gradient can be maintained as long as reduced NAD is available in the
mitochondrion. Explain the reasons for reduced NAD being required to maintain a proton
gradient.
[2]
(c) The diagram below shows one stage of respiration in which reduced NAD is produced.
(i) Name chemicals P and Q.
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[1]
P ........................................................................... Q
...........................................................................
(ii) Where in the cell do the reactions shown in the diagram above occur?
[1]
(iii) Outline the pathway for the production of triose phosphate in glycolysis.
[3]
(d) (i) The reaction labelled R on the diagram on the previous page occurs in humans when there
are anaerobic conditions in a tissue.
Explain the biochemical reasons for carrying out the reaction, despite the fact that lactate is
toxic in high concentrations.
[3]
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(ii) Reaction R sometimes occurs in muscle fibres when a short burst of very rapid ATP
production is needed. Suggest a reason for this.
[1]
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Marking Scheme
1.
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2.
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3.
4.
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5.
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6.
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7.
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8.
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9.
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10.
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11.
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12.
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13.
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Examiner's Comments
1. A well answered question in general. However, some confusion was seen between mitochondria
and chloroplasts and in identifying the regions where different stages of respiration takes place; a
number identified substance W as ATP rather than carbon dioxide and quite a few were unable to
identify where substrate-level phosphorylation occurs.
This comment originally referred to question 6 on paper 1074/01 (11/01/2013)
2. A substantial majority of candidates were awarded all three marks for part (a). In part (a) (i) some
candidates failed to label the base or labelled it incorrectly. In part (a) (ii) the most common errors
were 'andenine triphosphate' and 'andenosine triose phosphate.'
In part (b) (i) there were some very poor drawings despite only having to copy them from part (a).
Most candidates were able name an intracellular energy requiring process for part (b) (ii).
In part (c) the table was correctly completed by fewer candidates than expected, apart from not
getting the numbers of molecules right, many candidates did not describe both matrix and
mitochondria for precise location. Parts (c) (ii) and (iii) were generally well answered.
There was some confusion with anaerobic respiration in animals in part (d) with 'lactic acid' being
given quite often.
This comment originally referred to question 1 on paper 1074/01 (13/06/2011)
3. There were some excellent responses to this question with candidates from a number of centres
having a good grasp of biochemical details. It was particularly pleasing to see good responses to
(d) although many failed to appreciate the importance of the term 'per turn of the cycle' in the
stem of the question. In (d) (iii) very few knew that the electron carrier system involving NAD has
three pumps whereas that involving FAD has two pumps.
This comment originally referred to question 6 on paper 1074/01 (24/01/2011)
4. Part (d) was poorly answered with the majority of candidates having little understanding of
respiration energy budgets.
This comment originally referred to question 4 on paper 1074/02 (24/01/2011)
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5. Often gained full/almost full marks, especially since it was largely recall. Part (a) was synoptic and
tested nucleotide structure with some common sense since they could use the description in the
stem of the question. It routinely gained full marks, as did (b)(iii)
, (iv) and (c). Part b)(i)
proved
difficult for some to describe and many resorted to diagrams which were credited.
Part(ii)
seemed to be an 'all or nothing' response. Either scripts referred to the fact that it did
not need oxygen (in glycolysis) or involve an ETC/electrochemical gradient/the process of
chemiosmosis/stalked particles/mitochondria and got both marks, or they simply thought that it
was used by simple organisms, had been discovered first and was therefore the oldest and got
nothing.
This comment originally referred to question 6 on paper 1074/01 (10/01/2014)
6. Candidates were able to identify where aerobic and anaerobic respiration takes place in a muscle
fibre and how lactic acid is produced in muscle fibres. Knowledge and understanding of the
oxygen debt was poor.
This comment originally referred to question 5 on paper 1074/02 (13/06/2014)
7. (a) (i) Most candidates understood that glycolysis takes place in the cytoplasm but a significant
number thought that it was matrix or 'cytoplasm' in the mitochondria.
(ii)
Candidates had a very sound understanding of the stages of glycolysis and the stages
where dehydrogenation, phosphorylation and splitting of hexose take place.
(iii)
Most candidates correctly stated that the net gain of ATP when one molecule of glucose
is broken down was two.
(iv) There was a very good understanding of the process of anaerobic respiration in muscle.
(b) (i)
There was a very good understanding of what happens to fats under aerobic conditions.
Most candidates correctly stated that fats were broken down into fatty acids and glycerol and
correctly stated how these were used, several candidates correctly stated that there was
more hydrogen and linked this to chemiosmosis.
(ii)
Most correctly stated that carbon dioxide was the form that carbon was excreted from
the body , there were some very interesting alternatives but alas incorrect.
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(iii)
Some candidates did state that increased levels of oxygen would be required when fats
are used as a respiratory substrate and that more carbon dioxide would be produced but
many candidates were unable to give a valid suggestion as to why fats were not used in
muscles as the main source of energy.
This comment originally referred to question 2 on paper 1074/02 (11/01/2013)
8. (a) Anaerobic respiration.
Before attempting an essay question it is advisable that candidates plan out their answers.
Many failed to do this and so did not appreciate the important points required by the question.
Although there were some good responses many candidates described only the breakdown of
pyruvic acid into lactic acid. In failing to describe the pathway of conversion of glucose to
pyruvate they were unable to achieve the maximum marks. Many concentrated only on the
removal of lactic acid.
(b) Fermenter.
It was pleasing to see some really good, detailed answers to this question.
This comment originally referred to question 8 on paper 1074/02 (24/01/2011)
9. This was designed to test the understanding of respiratory knowledge and proved to be an
excellent discriminating question. Only those who really understand respiration gained all marks
and their scripts were a real pleasure to mark - it is to be hoped they might put this knowledge
and ability to use in their future careers. Part (a) routinely gained the mark for the number of
carbons in the intermediates but, despite being asked for a precise explanation of how these
figures were derived could not explain their logic. Many answers referred to 6, 5 and 4 carbon
compounds and not the named intermediates in the diagram and had citrate being
decarboxylated not isocitrate. Parts (b) and (c) routinely gained full marks by those who knew the
work. Part (d) gave some unusual suggestions ranging from kidneys, small intestine, skin and
tongue. Only the best answers gained both marks with muscle, and the reasons why this was a
good tissue to choose. Parts (e), (f) and (g) required analysis of the information given and the
use of the Krebs cycle diagram. Some superb answers, but many scripts showed a poor grasp of
metabolic pathways and the use of enzymes to control them. Far too many simply stated that
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oxygen was not available and this led to the results stated. How people with mitochondrial disease
can survive at all if they can only respire anaerobically was not considered.
This comment originally referred to question 6 on paper 1074/01 (13/06/2014)
10. A substantial majority of candidates were awarded all three marks for part
(a). (a) (i) Some candidates failed to label the base or labelled it incorrectly. (ii) The most
common errors were 'andenine triphosphate' and 'andenosine triose phosphate.'
(b) (i) There were some very poor drawings despite only having to copy them from part (a). (ii)
Most candidates were able name an intracellular energy requiring process for part (b) (ii).
(c) (i) The table was correctly completed by fewer candidates than expected, apart from not
getting the numbers of molecules right, many candidates did not describe both matrix and
mitochondria for precise location
(ii)&(iii) Were generally well answered.
(d) There was some confusion with anaerobic respiration in animals, with 'lactic acid' being given
quite often.
This comment originally referred to question 1 on paper 1074/02 (13/06/2011)
11. Part (a) was well answered but for (b)(i) very few candidates scored full marks because they did
not know that carbon dioxide is given out between pyruvate and acetyl Co-A. The term
decarboxylation was well known but candidates often struggled to describe the removal of carbon
dioxide from the body. Few mentioned that it diffused from the mitochondria though many referred
to its transportation in the blood with few mentioning it diffusing into the alveoli before being
exhaled.
In answer to part (c) few candidates mentioned dehydrogenation via a series of intermediates.
Many talked about the removal of hydrogen without specific reference to hydrogen atoms or
protons. The answers to part (d) often referred to the production of lactate though often failed to
mention the regeneration of NAD.
This comment originally referred to question 2 on paper 1074/02 (11/06/2013)
12.
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12. Most candidates demonstrated an impressive knowledge of all stages of the respiratory cycle, the
only common error was to assume that oxygen is used in the link reaction, Krebs cycle and
Oxidative phosphorylation and that ATP is produced in the link reaction.
This comment originally referred to question 5 on paper 1074/02 (10/01/2014)
13. Apart from a very occasional 'cell membrane' for W and 'cytoplasm' for Z all sub-parts of part (a)
were well answered.
The role of NAD was well understood in part (b) though there was some confusion over oxidation
and reduction.
In part (c)(i)
, the vast majority of candidates were awarded the mark, however a very small
number reversed the ATP/ADP. Most candidates were able to state that the reactions take place
in the cytoplasm in part (c)(ii)
(c)(iii)
.The early steps of glycolysis were fairly well understood in part
, although a significant number of candidates failed to pick up all three marks.
Part (d)(i)
proved to be a challenge with relatively few candidates scoring all three marks. QWC
was an issue and a significant number of candidates made no attempt at an answer. Likewise, the
mark for part (d)(ii)
was awarded relatively infrequently, where it was it was usually for
describing low oxygen conditions.
This comment originally referred to question 5 on paper 1074/01 (11/06/2013)
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