C1.2 Cell respiration

a. used as a source/(temporary) store of energy / is the energy currency of the cell;

b. releases energy when converted to ADP/when a phosphate is removed;

c. amount of energy released can be used/sufficient for (many metabolic) tasks;

d. active transport/another valid example;

e. ATP to ADP conversion is reversible / ATP can be regenerated from ADP;

f. can be produced in different ways/using energy from different sources/by aerobic or anaerobic respiration;

g. stable within cell so does not release energy prematurely/before needed;

h. small molecule/soluble so can move easily/quickly (through the cell);

i. cannot diffuse through membranes so is not lost from cell/to the environment;

h. The idea of ATP being small/soluble
must be there along with its
moveability.

3

Marking guidance:

max

a. movement of cells/chromosomes and example of movement;
b. movement of flagellum/cilium;
c. endocytosis/exocytosis;
d. detachment of myosin heads from actin filaments / myosin heads change their angle/become cocked;
e. active transport and example of use of active transport;
f. anabolic reactions / polymerization example / example of synthesizing macromolecules;
g. generation of heat and to provide optimum temperature for enzyme activity / in homeostasis / to maintain body temperature;
h. phosphorylation of substrates in glycolysis;
i. phosphorylation of substrates in photosynthesis light-
independent reaction/Calvin cycle;

For a. accept descriptions of cells (e.g. amoeboid phagocyte
moving to site of infection) or chromosomes (e.g. anaphase,
chromosomes moving to opposite poles).
For d. ignore 'muscle contraction'.
For e. E.g. sodium-potassium pump (in neurons) / maintaining resting potential in neurons / generation of root pressure / villus epithelial cells / selective reabsorption in kidney.
For e. do not accept transport of large molecules as example.
For f. accept examples such as DNA replication / transcription / translation / and other examples of formation of
macromolecules.
For h. accept phosphorylation of glucose (to glucose-6-phosphate) or phosphorylation of fructose-6-phosphate (to
fructose 1,6-biphosphate).
For i. accept formation of triose phosphate and formation of ribulose bisphosphate (regeneration of RuBP).

5

Marking guidance:

max

A

The need for energy

a. life processes/active transport/metabolism/movement require energy;

b. ATP provides energy for cell processes;

c. energy need to break bonds in a substrate during enzyme reactions;

d. energy is required to synthesize ATP from ADP

OR

energy is released when ATP is hydrolysed;

Release of energy

e. cell respiration produces ATP using energy stored in carbon compounds/glucose/fatty acids;

f. aerobic respiration occurs in mitochondria;

g. aerobic respiration requires oxygen;

h. aerobic respiration provides more ATP/energy than anaerobic respiration;

i. cells use mainly glucose and/or fatty acids as a fuel/substrate for respiration;

j. in aerobic respiration carbon dioxide and water are waste products

OR
$$\text { fuel/glucose }+\mathrm{O}_{2} \rightarrow \mathrm{CO}_{2}+\mathrm{H}_{2} \mathrm{O} \text { (+ energy/ATP); }$$

k. anaerobic respiration (in humans) yields lactic acid as a waste product

OR

fuel/glucose → lactic acid (+ energy/ATP);

Correct equation can gain
marking points g. and j.
Equation does not need to be balanced.

8

Marking guidance:

max

anaerobic respiration: glucose transformed into (two molecules of) pyruvate/pyruvic acid; Accept this point in any part of the answer. oxidation reactions using NAD/NAD ${ }^{+}$/ producing reduced NAD/NADH; smaller amount of energy released/ATP produced than in aerobic; $\mathrm{NAD} / \mathrm{NAD}^{+}$regenerated by reducing pyruvate/transfer of hydrogen to pyruvate; pyruvate to $\mathrm{CO}_{2}$ and ethanol in yeast/in alcoholic fermentation; pyruvate to lactic acid in humans/in lactic/lactate fermentation; aerobic respiration: pyruvic acid/pyruvate fully oxidized/fully broken down; by the link reaction and Krebs cycle; reduced NAD/NADH passes electrons to electron transport chain; proton $/ \mathrm{H}^{+}$gradient generated; oxygen required as terminal electron acceptor; proton gradient used by ATP synthase/synthetase to produce ATP;

a. more oxygen in inhaled air than in exhaled air

OR

mouse uses oxygen in respiration

b. carbon dioxide exhaled / produced by mouse is absorbed by the soda lime

c. difference in volume is oxygen used by mouse

OR the volume/concentration/pressure of oxygen in the jar falls

d. «this» sucks the coloured liquid up the tube

e. volume of oxygen consumed equals the increase in volume of coloured water in the tube

Source/mouse must be mentioned for marking point b - not just "sodalime absorbs $\mathrm{CO}_{2}$ ".

3 max

D

occurs in cytoplasm (of cell); substrate is hexose/glucose/fructose; phosphorylation of glucose/fructose/hexose; to form hexose diphosphate/glucose 6-phosphate; requires ATP; glucose/fructose/hexose (diphosphate) converted into (two) pyruvates/three
carbon compounds; oxidation;
to produce (two) $\mathrm{NADH}+\mathrm{H}^{+}$/ (two) reduced NADs;
net gain of two ATP (per glucose);

Marking guidance:

[6 max]

a. NADH transfers electrons to pyruvate

OR

pyruvate acts as electron acceptor / pyruvate is reduced;

b. (pyruvate) converted to lactate;

c. NADH oxidized/converted to NAD

OR

NAD available to be reduced/converted to NADH again (in glycolysis);

2

Marking guidance:

max

a. Saccaromyces yeast used;
b. yeast ferments sugars/glucose anaerobically;
c. amylase released by germinated grain/barley/cereals breaks down starch (in seeds) to sugar;
d. $\mathrm{CO}_{2}$ and ethanol produced in beer and bread production;
e. $\mathrm{CO}_{2}$ raises/leavens/expands bread dough;
f. $\quad \mathrm{CO}_{2}$ remains (partially) dissolved in beer/gives beer its bubbles/carbonation;
g. during baking ethanol evaporates from bread;
h. baking kills the yeast/stops fermentation;
i. ethanol produced in beer (eventually) kills yeast cells/stops fermentation by yeast; j. by-products / different yeast varieties give different beers/flavours;

Marking guidance:

Award [5 max] if only mentions one of the two processes.

C3. pyruvate (from glycolysis) enters a mitochondrion; enzymes in the matrix remove one carbon dioxide and hydrogen from the pyruvate; hydrogen is accepted by NAD/forms NADH; removal of hydrogen is oxidation; removal of carbon dioxide is decarboxylation; the whole process/link reaction is oxidative decarboxylation; the product is an acetyl group which reacts with CoA / coenzyme A; acetyl CoA enters Krebs cycle; Accept any of the above points in the form of a clearly drawn and correctly labelled diagram.

Krebs cycle only occurs in aerobic conditions; the Krebs cycle occurs in the mitochondria; acetyl CoA from the link reaction releases an acetyl group; $\mathrm{NADH}+\mathrm{H}^{+}$and $\mathrm{CO}_{2}$ are formed (with each decarboxylation); decarboxylation/removal of $\mathrm{CO}_{2}$ involves oxidation/oxidative decarboxylation; and the release of energy; acetyl group is joined to a 4-carbon molecule/ $\mathrm{C}_{4} /$ oxaloacetate to form a 6-carbon molecule/citrate;
(decarboxylation changes citrate) to 5-carbon molecule/ $\mathrm{C}_{5}$; (decarboxylation changes glutamate) to a 4-carbon molecule/ $\mathrm{C}_{4}$; then converted into the original 4-carbon molecule/ $\mathrm{C}_{4} /$ oxaloacetate and the cycle repeats;
one (molecule) of ATP is made during this step; reduced H-carriers/ NADH and FADH2 and carbon dioxide are end-products of Krebs cycle;

Z

C

a protons pumped across inner membrane of mitochondria/into intermembrane space;

b using energy released by flow of electrons/by electron transport/by electron carriers;

c proton gradient established/maintained/ proton motive force generated;

d protons pass/diffuse back through inner membrane/membrane of cristae/to matrix;

e through ATP synthase;

f ATP production coupled to flow of protons / ATP from ADP and Pi using energy from protons;

Marks can be awarded in an annotated diagram

4 max

a. terminal/final electron acceptor

b. at the end of electron transport chain

c. oxygen also accepts protons/hydrogen ions

d. water produced/ $\frac{1}{2} \mathrm{O}_{2}+2$ electrons $+2 \mathrm{H}^{+} \rightarrow \mathrm{H}_{2} \mathrm{O}$

e. helps to maintain proton gradient «across inner mitochondrial membrane by removal of protons from the stroma»

f. oxygen is highly electronegative/electrons strongly attracted to oxygen

g. avoids anaerobic respiration/buildup of lactic acid

h. allows more electrons to be delivered to the electron transport chain

OR allows NADFAD to be regenerated/reduced NAD/FAD converted back to NAD/FAD

i. oxygen allows maximum yield of energy «from glucose» allows complete oxidation of glucose/allows fats to be used in respiration

5 max

more mitochondria means more aerobic respiration;
more mitochondria in swimming muscles;
products of fatty acid oxidation could be used in respiration (so hypothesis could be supported);
increase in HAD activity would mean an increase in fatty acid oxidation;
little/no increase in HAD activity in swimming muscles (so hypothesis not supported);
during diving low oxygen/hypoxic conditions so high HAD activity/ mitochondrial concentration allows aerobic metabolism to continue;