Exam Qs

Question 1

During the cycle ornithine moves into organelle D and citrulline moves out of the organelle.
Suggest the method by which these molecules move into and out of the organelle during the cycle. Give
reasons for your choice

Answer 1

either
facilitated diffusion (1)
conversion of ornithine into citrulline creates concentration gradients
or
(molecules are not lipid soluble so) require protein channels to cross membrane (1) or
active transport (1)
ornithine and citrulline need to be moved into and out of D
more quickly than would be met by diffusion (1)

Question 2

How has the ammonia that is used in step 1 been formed?

Answer 2

deamination / removal of NH2 group from amino acid (1)

Question 3

What is the role of pyruvate in anaerobic respiration?

Answer 3

is a hydrogen acceptor / removed hydrogen from reduced NAD

Question 4

Why is it important that compound G is formed during the reaction in which compound D is converted into
compound E in anaerobic respiration?

Answer 4

two from
for glycolysis to take place, NAD / G, is needed (1)
there is a limited amount of NAD in the cell (1)
formation of, NAD / G, allows, glycolysis to continue / some ATP to be formed (1)

Question 5

Athletic sprinters require large amounts of energy in short periods of time. Many elite sprinters can run 100 metre races in under 10 seconds.
Under normal conditions, exercise requires an increased rate of breathing. It has been observed that some of the best sprinters only take one breath at the start of the race and do not inhale again until the end of the race.
Suggest how these sprinters can expend so much energy without needing to carry out aerobic respiration.

Answer 5

two from
cells are able to tolerate, high levels of lactate / acidity / low pH (1)
have high phosphocreatine stores (1) use of stored ATP (1)

Question 6

The light-independent stage requires coenzymes. For example, NADPH reduces molecules by adding electrons, and ATP phosphorylates molecules by adding phosphate groups.
Coenzymes are involved in other cellular processes, including respiration.
Summarise the importance of coenzymes in respiration. You should include details of the molecules and processes involved.

Answer 6

Coenzyme A:
transfers acetyl / acetate / 2C from
link reaction to Krebs cycle ADP/ATP:
phosphorylation of / addition of phosphate group to, glucose to form hexose-1, 6-bisphosphate in glycolysis
dephosphorylation of / removal of phosphate group from, TP in glycolysis
dephosphorylation of / removal of phosphate group from, intermediate in Krebs cycle formation from substrate level phosphorylation
formation from oxidative phosphorylation, harnessing chemical energy from chemiosmosis / proton motive force
NAD:
oxidation of / removal of H / removal of electrons from, triose (bis)phosphate in glycolysis oxidation of / removal of H / removal of electrons from, pyruvate in link reaction
oxidation of / removal of H / removal of electrons from, intermediates in Krebs cycle reduction of / addition of electrons to, electron transport chain / cytochrome in oxidative phosphorylation
reduction of / addition of electrons to, pyruvate in lactate fermentation reduction of / addition of electrons to, ethanal in alcoholic fermentation
FAD:
oxidation of / removal of H / removal of electrons from, intermediates in Krebs cycle

Question 7

Respiration is an important metabolic process that takes place in all living cells. What is the precise location of the link reaction within cells?

Answer 7

matrix of mitochondrion

Question 8

Herbicides work in a number of different ways.
(i) Some herbicides, known as phenoxy herbicides, mimic the action of the auxin, indoleacetic acid (IAA). What is the normal action of IAA in plant cells?

Answer 8

(stimulates) cell, elongation / division

Question 9

The herbicide atrazine works by disabling plastoquinone, one of the proton pumps in photosystem II. Explain how atrazine would kill a susceptible plant.

Answer 9

three from
1 reduced / no, proton pumping / proton motive force / chemiosmosis (1)
2 photophosphorylation stops (1)
3 less / no, ATP produced (1)
4 less / no, reduced NADP produced (1)
5 no, Calvin cycle / carbon fixation / light
independent stage (1)
plus
6 no, TP / (hexose) sugars, made (1) 7 no respiratory substrate / respiration
ceases (1)

Question 10

Botulism is a condition resulting from the action of botulinum toxin. The main symptom of botulism is skeletal muscle weakness, which can be fatal.
(i) Botulinum toxin is produced by the anaerobic bacterium Clostridium botulinum. What information does the word ‘anaerobic’ suggest about the bacterium?

Answer 10

it (only) respires in the absence of oxygen

Question 11

The toxin is initially produced as a large single polypeptide that has low potency.
After the toxin has been acted upon by a protease, two chains are produced which remain connected by a disulfide bond. In this form it is far more toxic.
Describe the action of the protease when it acts on the toxin.

Answer 11

it hydrolyses a peptide bond between two amino acids (residues) which are joined by a disulfide bond

Question 12

The toxin acts primarily at the cholinergic nerve terminals of stimulatory motor neurones. Part of the molecule binds irreversibly to specific receptors on the presynaptic membrane. The toxin–receptor complex is then
taken into the cytoplasm of the neurone where the disulfide bond is broken, releasing the section of the molecule which acts to block the release of the neurotransmitter.
Explain why botulism can be fatal.

Answer 12

two from
intercostal muscles are / diaphragm muscle is, weakened / paralysed (1) idea that ventilation and oxygenation of blood is, reduced / compromised (1) cells / (named) organ(s), cannot, obtain oxygen for respiration / carry out aerobic respiration (1)

Question 13

Termites are highly social insects. They are thought to have evolved from earlier forms of insect at least 150 million years ago, in the Jurassic geological period. They are related to cockroaches.
(i) How might scientists a century ago have known that termites evolved in the Jurassic geological period?

Answer 13

ossils in, known-age / Jurassic, strata / rocks

Question 14

What new source of evidence might help today’s scientists to find out how closely related termites are to cockroaches?

Answer 14

DNA / cytochrome c

Question 15

Fig. 5.1 shows a termite mound, the nest of approximately one million individuals. The photograph was taken in Queensland Australia, about 3000 kilometres south of the equator.
(i) Fig. 5.1 shows that the interior of the termite mound is full of interconnecting chambers. At the top of the mound some of these chambers open to the air outside.
Worker termites spend all their time working in brood chambers low in the mound, where eggs and larvae develop.
Explain how carbon dioxide produced in the respiring body cells of worker termites is removed to the air outside the termite mound

Answer 15

carbon dioxide diffuses down concentration gradient out of the respiring cell (1)
carried through body from cell (to tracheoles) by blood passing out via tracheoles / trachea / spiracles (1) respiration generates heat (1)
hot gases expand and are less dense so rise up by convection through the mound to vents at mound-top (1)

Question 16

In Africa, closer to the equator, the mounds built by some species of termite are blade-shaped, with the long axis pointing North–South. Fig. 5.2 shows an example of a termite mound in Africa.
Suggest why the African termites need to build mounds in this shape and orientation.

Answer 16

shape, large or increased surface area to volume ratio (1)
smallest area exposed to greatest heat (1)

Question 17

ATP is produced in two different ways during respiration.

Some ATP is produced at the points labelled W.
ATP is also produced using reduced NAD and reduced FAD on the inner mitochondrial membrane.
Outline the differences in the two ways by which ATP is produced in respiration.

Answer 17

by substrate level phosphorylation;
detail;
by, chemiosmosis/ oxidative phosphorylation;
detail;

Question 18

Suggest one other use of amino acids in liver cell metabolism.

Answer 18

1 in respiration / in Krebs cycle / as a respiratory substrate;
2 gluconeogenesis;
3 conversion to, lipid / fatty acid;
4 transamination

Question 19

Describe the pattern of respiration shown by cauliflower at increasing storage temperatures of 0 °C to 20 °C.

Answer 19

1 (as the temperature increases) the respiration rate increases;
2 respiration rate doubles with a 10°C temperature increase;
3 comparative figures with correct units (units once for respiration and once for temperature) in the context of either mp

Question 20

Discuss what the data in Table 5.1 indicate about the best conditions for storage of fruits and vegetables.

Answer 20

1 best conditions are low( er) temperatures because respiration rate low;
2 0°C / freezing, could be / is, best;
3 idea that 0°C might be too low as (the
food cells) might be damaged at 0°C;
4 idea that for some (named) food(s) (storage) temperature doesn’t seem to matter;
5 idea that data is incomplete for, potato / parsnip, so, only limited / no, conclusions can be made;
6 idea that if product needs to ripen during storage then a higher temperature (not above 20°C) will be ideal;

Question 21

Identify, with reasons, which fruit or vegetable listed in Table 5.1 is least likely to spoil during storage.

Answer 21

1 onion;
2 has low( est) respiration rate; 3 across all temperatures (in the
investigation / up to 20°C)
or
temperature has, the least / little, effect on respiration rate;
4 can be, stored / kept, at, higher temperatures / room temperature / at 20°C;

Question 22

Which fruit or vegetable listed in Table 5.1 is likely to be the most difficult to keep fresh during storage? Give a reason for your answer.

Answer 22

asparagus
and
has a high respiration rate across all temperatures / has the highest respiration rate (of the foods);

Question 23

Respiration can be aerobic or anaerobic.
(i) Certain parasites live in the blood of mammals.
Suggest why, even though blood carries oxygen, these parasites are adapted to respire anaerobically.

Answer 23

1 idea that parasites have little access to oxygen;
2 (inaccessible because)
little oxygen dissolved in plasma / oxygen not very soluble (in plasma);
3 (inaccessible because) idea that oxygen is,
combined with haemoglobin /
contained in red blood cells;
4 idea that haemoglobin has greater affinity for oxygen than parasite (pigment)

Question 24

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.

Answer 24

in animals
A1 pyruvate is, converted / reduced, to, lactate / lactic acid;
A2 can be reversed as no, atoms lost / other product formed;
A3 lactate dehydrogenase available to reverse the reaction;
in yeast
Y1 pyruvate converted to ethanol (in 2 steps) and carbon dioxide / CO2;
Y2 cannot be reversed as, carbon dioxide is / atoms are, lost;
Y3 (de)carboxylase enzyme cannot reverse the reaction;

Question 25

A mixture of three sugars is added to batch fermenter at the beginning of the process:
the monosaccharide glucose, which the yeast uses up first, during days 0 to 2 the disaccharide maltose, which is used during days 1 to 5
the trisaccharide maltotriose, which is used during days 4 to 6.
Suggest why the yeast uses the sugars in this order.

Answer 25

1 glucose can, be used / enters glycolysis, directly / without being broken down (first);
2 maltose, must, be hydrolysed / have glycosidic bonds broken;
3 enzyme / maltase, only made when, needed / maltose present / glucose running out;
4 enzyme induced / gene(s) switched on; 5 transcription and translation / protein
synthesis, takes time;
6 maltotriose requires, more (2) hydrolysis (reactions) / breaking of more (2) glycosidic bonds
or
enzyme to break down maltotriose made last

Question 26

Why does aerobic respiration yield fewer molecules of ATP than the theoretical maximum?

Answer 26

some ATP used to (actively) transport pyruvate (into the mitochondrion);
some ATP used to (actively) transport H(+) from (reduced) NAD, formed in glycolysis / into the mitochondrion;
some energy released in ETC, is not used to transport H+
(across inner membrane) / is released as heat;
not all the H+ movement (back across membrane), is used to generate ATP / is through ATP synth(et)ase;
not all the, reduced NAD / red NAD / NADH, is used to feed into the ETC

Question 27

(b). Explain why the incomplete breakdown of glucose in anaerobic respiration produces less ATP than aerobic respiration.

Answer 27

in anaerobic respiration
1glycolysis / conversion of glucose into pyruvate, occurs;
2produces 2 molecules of ATP (net);
3(only) substrate level phosphorylation (occurs);
4oxygen not available as final electron acceptor;
5pyruvate / ethanal,
used to regenerate NAD for glycolysis (to continue);
6(Krebs cycle and)
electron transport chain / chemiosmosis / oxidative phosphorylation, do not occur

Question 28

What properties of the mitochondrial inner membrane allow chemiosmosis to occur?
[2]

Answer 28

(mostly) impermeable to H+ ions / protons ✓
large surface area ✓
presence of, ATP synthase / stalked particles ✓

Question 29

Describe two quantitative changes in region P which occur as a result of oxidative phosphorylation.

Answer 29

pH decreases
AND
becomes more positive(ly charged) ✓

Question 30

*Some individuals can eat large quantities of fatty and carbohydrate-rich food without putting on weight. One possible hypothesis that could explain this is related to the mitochondrial inner membrane.
Scientists have suggested that some individuals may have a larger number of proton pores in their inner mitochondrial membrane than normal.
Explain how having a larger number of proton pores in the inner mitochondrial membrane would result in a person being less likely to gain weight.

Answer 30

larger number of protons pores results in protons leaking back into matrix reduces yield of ATP from chemiosmotic gradients
less ATP is made from oxidative phosphorylation
more energy wasted as heat
energy from chemiosmosis decoupled from ATP synthesis
energy yield from aerobic respiration reduced per molecule of glucose
food not converted to ATP as efficiently less excess energy intake in diet
less deposition of fat
fat stores may be respired for energy

Question 31

Use the information in Table 21 to deduce which of the two cookies is the protein cookie. Explain your choice.

Answer 31

cookie 2 is protein cookie ✓
RQ of cookie 2 is 0.94 AND RQ of cookie 1 is 0.98 ✓
lower RQ means (cookie 2) must have more protein ✓
RQ closer to 1.0 means more carbohydrate ✓

Question 32

The student then changed the experiment to investigate whether respiration of the cookies by yeast was different from respiration of the cookies by maggots.
The student planned to allow yeast cells and maggots to respire the cookie powder in anaerobic conditions and measure the RQ over 2 minutes.
State and explain one problem with the student’s method

Answer 32

maggots will not produce CO2, during lactate fermentation ✓
yeast will produce CO2, during alcoholic fermentation ✓
measuring RQ requires CO2 production / RQ value (for maggots) will be lower than normal ✓
OR
2 minutes not long enough for, yeast / maggots, to, break down / respire, cookie ✓
CO2 produced (by yeast) is not from respiration of cookie ✓
RQ (comparison) will be invalid ✓