Sample cover letter for Internship position at Citi

Mark Scheme: 3.5.1: Stimulus and Response

M1. (i) kinesis;
movement is random / rate of turning changes /
does not move towards/away from light;

2

(ii) advantage related to light/shade;
e.g. remains in shade so avoids predators

1

[3]

M2. (a) B – It is the 2^nd contraction / occurs (immediately) after A / occurs
after atrium;
Larger / more force / more pressure;

2

(b)

= 37 to 38

allow 1 mark if correct working shown

max 2

(c) (i) (Heart rate) reduced;
(Stroke volume) no effect;

2

(ii) Reduced because C.O. = H.R. x S.V. / connection argument based on
reduced H.R;

1

(iii) Parasympathetic;

1

(d) (i) 1. Coordination via medulla (of brain) / cardiac centre;
2. (Increased) impulses along sympathetic (/ cardiac accelerator)
nerve;
3. To S.A. node / pacemaker;
4. Release of noradrenalin;
5. More impulses sent from / increased rate of discharge of
S.A. node / pacemaker;

Not “beats”; not “speeds up”

6. Increased heart rate / increased stroke volume;

max 4

(ii) In exercise – More energy release / more respiration / actively
respiring muscles / for aerobic respiration;
Higher cardiac output – Increases O₂ supply (to muscles);
Increases glucose supply (to muscles);
Increases CO₂ removal (from muscles) /
lactate removal;
Increases heat removal (from muscles) /
for cooling;

If no “increase” – max 2 marks

3

[15]

M3. (a) (i) 1 and 2 share neurone but 2 and 3 have separate neurones (to brain);

Ignore wrong names of neurones

1

(ii) 1 unit is sub-threshold / 3 units are above threshold / give sufficient
depolarisation;
(1 unit) No impulses / no action potential / in (sensory) neurone /
does not stimulate (sensory) neurone / 3 units → impulses;
(Spatial) summation / sufficient neurotransmitter released / from
3 receptors / insufficient N-T from one;
Reject ‘temporal’

3

(b) (i) (Three) different types of (cone) cells / types 6 and 7 sensitive
to different wavelengths / different frequencies / different colours;

(ii) Impulses along separate neurone from each receptor cell / each
receptor cell connects to separate neurone;

2

[6]

M4. (a) medulla;

1

(b) A increase
B increase;

1

(c) it spreads through the atria / right atrium / through cardiac muscle;
to the atrioventricular node;
then through conduction fibres / bundle of His/Purkyne fibres);

3

[5]

M5. (i) no (photo)receptor cells at Y/no rods and cones;

1

(ii) X has many / only cones / more cones than Z;
which each synapse to a single neurone / bipolar cell / no
retinal convergence;
ORZ has mainly rods/more rods than cones;
which share/converge on neurones/bipolar cells;

2

[3]

M6. (a) kinesis;(ignore ‘ortho-’ / ‘klino-’, allow ‘thermo-’, reject ‘photo-’ / ‘chemo-’ / etc)

random movements = 1 mark, eg
/ degree of turning / number of turns depends on strength of stimulus /
on temperature/ allow specific ref. to more turning at 35° than at 30° /
non-directional stimulus/response;

ignore ‘speed’

2

(b) stays longer in warmer area / at 35° / tends to leave cooler area /
to leave 30° / stays in favourable conditions ;

remains near food source / on host;

2

[4]

M7. (a) (i) presence of -COOH group;

1

(ii) similar structure so fit same protein / receptors;

1

(b) 2,4-D adds to effect of IAA (already present) / affects all cells;
stimulates growth in parts other than growing points / stimulates
uncontrolled growth / makes walls of cells stretch too much /
makes growth outstrip nutrient availability;

2

[4]

M8. (i) rhodopsin bleached/broken down by light;
time for resynthesis;

2

(ii) rhodopsin/pigment absorbs green light more readily than red / is
more sensitive to green light;
(after resynthesis) less (intense) green light needed to break down
rhodopsin (than red);

2

(iii) white has (high proportion of) wavelengths to which rhodopsin not
sensitive;

1

[5]

M9. (a) (i) arc shows 3 neurones;

(3 distinct neurones, one of which is in the grey matter, with correct route through dorsal and ventral roots and indication of synapses. Ignore position of cell bodies.)

1

(ii) neurones labelled sensory, relay/intermediate, motor;

1

(iii) muscle labelled as effector;

1

(b) impulses to brain;

(reject signal, message, information)

1 max

[4]

M10. (a) (i) majority of larvae move to sectors on opposite side to lamp;
(reject largest number/most in sector 19)

1

(ii) use heat filter in front of lamp

(allow lamp not too close);

rotate card and lamp to eliminate magnetic field;
alter direction of larval head when releasing;
(reject general references to keeping variables constant)

1 max

(iii) wide beam from lamp;
variability of organisms;
positioning of larvae variable;

1 max

(b) idea of middle value;
method of determining middle value in rank order, e.g. sector in which
300/2 occurs;

2

[5]

M11. (a) 1. rate of respiration increases (in muscle cells);
2. carbon dioxide concentration increases / pH falls / H⁺ increases /
acidity increases;
3. in blood plasma;
4. chemoreceptors;
5. in aortic / carotid bodies / medulla (accept reference to aorta /
carotid arteries not sinus);
6. (impulses to) medulla / cardioaccelerator centre;
7. increased frequency of impulses (award only once);
8. along sympathetic pathway;
9. to sinoatrial node/SAN (not pacemaker);

6 max

(b) (i) through cardiac muscle;
to atrioventricular node;
along bundle of His / Purkyne fibres;

2 max

(ii) sinoatrial node in the (right) atrium;
trace from healthy person is identical to the trace for the diseased
heart in the region of the atria / only differences seen in
trace for ventricles;

2

[10]

M12. (a) chloroplast, so cell photosynthesises;
moves to optimum/best light intensity for photosynthesis;
avoids damage due to bright light;

2 max

(b) (i) 2700

1

(ii) = 27 225 000 / 27 × 10⁶ = 2 marks

(allow 1 mark for principle: )

2

(c) (i) rate slightly slower / not affected in first 20/30 minutes / lower
peak than control;
then decreases/ much lower (than control);

(allow 1 mark for increase in first 20/30 minutes, then decreased, if not compared with control/normal)

(disqualify flagellum grows longer)

2

(ii) 1. actinomycin has no effect (on growth of flagella);
even though mRNA production / transcription prevented;

(accept references to ‘expt 1’)

2. (re)growth little affected by puromycin at first;
protein synthesis inhibited, so likely to be using proteins
present;

4

[11]

M13. (a) one mark for conclusion:maggots move to/respond to/prefer/like /red rather than green;

(reject ‘most prefer red’)

maggots move to/prefer/like areas of lower light intensity (except green);
maggots respond more to colour than light intensity / do not respond to
differences in light intensity;

(reject conclusion relating to single result)

one mark for:evidence matching conclusion:
more in red than green, but light intensity the same;
more in segments with lower light intensity;
more differences in different colours, little difference in light intensity;
large difference in number of maggots on segments with 25 a.u.
light intensity;

2 max

(b) valid statement expressed as null hypothesis, i.e. in negative
form, e.g. no difference in response to different colours / light intensities;

(must relate to a possible hypothesis)

1

(c) rotate box (so segments in different direction) / change order of coloured
segments;
place magnets around box / create alternative magnetic field;

1 max

[4]

M14. (a) moves to 40 °C side, then later to 20 °C;
gets lighter in hot side and darker in cool side;
lighter as it absorbs heat/darker as it loses heat;
by conduction/convection/radiation;

3 max

(b) lizard finds favourable environment;
(helps it to) maintain constant body temperature;
advantage of this, e.g. for enzyme activity;

2 max

(c) receptors in blood vessels/skin;
nerve impulses produced;
go to coordinator/brain/hypothalamus;
motor neurones send nerve impulses;
to effectors/muscles;

3 max

[8]

M16. (a) no rods at blind spot or fovea;

greater distribution of rods at edge;

2

(b) more rods and no / fewer cones present;

rods at the fovea / rods not mainly at periphery;

rods have high sensitivity / show retinal convergence /
converse for cones;

rhodopsin ‘bleached’ at low light intensities / iodopsin ‘bleached’;

at high light intensities;

3 max

[5]

M17. (a) pupae survive the winter;
conserves fat/energy stores;
(reject reference to pupa feeding)when no food/plants (for larva/adult);
temperature too cold for survival;

3 max

(b) dark period important;
group B has longer light period than group A but no diapause
(so not long light induced);
interruption of dark period in group C leads to no diapause
(so uninterupted dark period needed);

3

[6]

M18. (a) 1 pressure receptors / baroreceptors / stretch receptors;
2 in aorta / carotid arteries / carotid sinus; (reject carotid body)3 send impulses;
(reject signals / messages / electronic)4 to cardiovascular centre / medulla / cardio-inhibitory centre;
5 send impulses;(once only)6 parasympathetic nerves / vagus; (accept inhibitory nerve)
7 to SAN;
8 release of ACh / inhibits SAN / decreases impulses from SAN;
9 decreases impulses to AVN / decreased stimulation of AVN /

decreases impulses from AVN;

(any reference to signals / messages / electronic disqualifies points 3 and 5 only)

6 max

(b) 1 inhibit impulses in sympathetic nerves / from cardio-acceleratory centre;
2 SAN not stimulated / noradrenaline not released /
(accept inhibits / blocks synapses);3 heart rate lowers / does not increase;

2 max

[8]

QWC 1