AQA A Level Biology Paper 2 2021 Mark Scheme

Question Marking Guidance Mark Comments

01.1

1. Phosphorylation of glucose using ATP;

2. Oxidation of triose phosphate to pyruvate;

3. Net gain of ATP;

4. NAD reduced;

4 max

Accept all mark points

in diagrams.

2. Accept removal of

hydrogen from triose

phosphate for

oxidation.

3. Accept any

description that

indicates a net gain

e.g., 4 produced, 2

used.

4. Accept

NADH/NADH2/NADH

+ H+

produced.

Question Marking Guidance Mark Comments

01.2

1. Less/no reduced NAD/coenzymes

 OR

 Fewer/no hydrogens/electrons removed (and

passed to electron transfer chain);

2. Oxygen is the final/terminal (electron) acceptor;

2

1. Accept less/no FAD

reduced.

MARK SCHEME – A-LEVEL BIOLOGY – 7402/2 – JUNE 2021

5

Question Marking Guidance Mark Comments

02.1

1. Higher concentration of potassium ions inside

and higher concentration of sodium ions outside

(the neurone)

 OR

 potassium ions diffuse out

 OR

 sodium ions diffuse in;

2. (Membrane) more permeable to potassium ions

(leaving than sodium ions entering)

 OR

 (Membrane) less permeable to sodium ions

(entering than potassium ions leaving);

3. Sodium ions (actively) transported out and

potassium ions in; 3

1. Accept ‘more’ for

‘higher concentration’.

1. Accept ‘sodium

ions can’t diffuse in

(due to alternative

explanation).

2. Accept for ‘less

permeable to sodium

ions’ is ‘impermeable

to sodium ions’ or

‘sodium

gates/channels are

closed’ (alternative

explanation).

1, 2 and 3 reference

to ions or Na+

and K+

is required. If

mentioned once allow

for all mark points.

1, 2 and 3. If an

answer provides two

or three of these mark

points without any

reference to ions –

award one maximum

mark.

3. Accept 3 Na+

out

and 2 K

+

in but reject

if numbers used are

incorrect.

Question Marking Guidance Mark Comments

02.2

1. Myelination provides (electrical) insulation;

2. (In myelinated) saltatory (conduction)

 OR

(In myelinated) depolarisation at nodes (of

Ranvier);

3. In non-myelinated depolarisation occurs along

 whole/length (of axon);

3

1. Reject thermal

insulation.

1. Accept description of

(electrical) insulation.

3. Accept action potentials

for depolarisation.

2 and 3. ‘Messages’ or

‘signals’ disqualifies first of

these marks credited.

MARK SCHEME – A-LEVEL BIOLOGY – 7402/2 – JUNE 2021

6

Question Marking Guidance Mark Comments

02.3

1. No/less ATP produced;

2. No/less active transport

OR

Sodium/potassium pump inhibited;

3. Electrochemical gradient not maintained

OR

(Facilitated) diffusion of ions causes change to

0 mV

OR

(Results in) same concentration of (sodium and

potassium) ions (either side of membrane)

OR

No net movement of (sodium and potassium)

ions;

3

2. Accept Na+

not/fewer moved out

and K+ not/fewer

moved in.

3. Accept reaches

electrical

equilibrium/balance.

3. Accept

concentration gradient

of sodium and

potassium ions not

maintained