Author: philcolls76@outlook.com
Last saved by: Gareth Roberts

Carmel College

M1.          (a)     To sterilise/kill bacteria;
So that only one kind of bacteria present on agar plate/to prevent contamination
(by bacteria);
2

(b)     Clear zone / inhibition zone is where bacteria have not grown/been inhibited/killed;Antibiotic diffuses out of paper disc/into agar;Bacterium A inhibited/killed by tetracycline/tetracycline has little effect on
bacterium B;Bacterium B inhibited/killed by penicillin/bacterium A resistant to penicillin;Both kinds of bacteria resistant to streptomycin;
Q Ignore references to ‘immune’
4 max
[6]

M2.          (a)     (i)      to increase surface area (for carbon dioxide absorption);
1
(ii)     oxygen is used / carbon dioxide emitted is absorbed; 
so decrease in volume / pressure;
2
(iii)     change of level of (manometer) liquid over time;
bore of tube;
mass of snails;
time interval;
3 max

(b)     (i)      valid similarity taking into account SD e.g. between 5 and 15 °C
both show little effect of temperature / intakes similar
between 5 and 15 °C;
1
valid difference taking into account SD above 15 °C e.g.
rise at 20 °C and above is less when snails kept in sea water;
1
(ii)     standard deviations high;
means unreliable;
(accept 25 °C being out of normal range for snail / 
not enough temperature readings for 1 mark)
2
[10]

M3.          (a)     random sampling method; 
use of large numbers / many / 10 or more quadrats in each area;
counting daisies and dividing by area;
3
(b)     the cutting has no effect;
1

(c)     daisy, dandelion, buttercup show (statistically) significant differences;
no significant effect on plantains;
comment on relative significance of daisy / dandelion / buttercup;
regular cutting linked to significant increase in density of daisy / dandelion;
linked to significant decrease in density of buttercup;
(no marks if significance idea omitted)
3 max
[7]

M4.          (a)     the more light absorbed, the greater the rate of photosynthesis;
light provides the energy for light dependent reactions / photolysis / 
light independent reactions / production of reduced NADP / 
exciting electrons in chlorophyll;
(do not give credit if energy is used in photosynthesis)
2
(b)     count the number of bubbles / measure the volume of gas / measure the 
change in pH / carbon dioxide / hydrogen carbonate ions;
(credit oxygen produced)
1

(c)     530 – 630 nm;
(any values within this range)
limited absorption of light / (green) plants reflect green light / 
limited photosynthesis at these wavelengths of light;
(allow references to no light absorbed or no photosynthesis)
2
(d)     (i)      chlorophyll excited / reduced NADP formed;
electrons from chlorophyll / reduced NADP changes the dye colour;
2
(ii)     ADP and phosphate needed to produce ATP / ATP is a product of 
the light dependent reactions;
ADP levels are a limiting factor;
(must explain the idea of limiting factors – do not credit answers like more ADP causes more photosynthesis) 
2
[9]

M5.          (a)     (i)      A = phospholipid
B = protein;
(both correct)
1

(ii)     allows movement of lipid soluble / non-polar molecules / named
e.g. water / gases;
prevents movement of water soluble / polar molecules / named
e.g. ions / amino acids;
idea of selection / membrane partially / differentially permeable / 
large molecules do not move through, small molecules do;
(accept semi-permeable)
2 max

(b)     (i)      diffusion
(reject facilitated)
1
(ii)     higher rate of exchange / diffusion;
prevents cooling of the blood / prevents increase in viscosity;
2

(iii)     concentration gradient maintained / equilibrium never achieved;
blood always meets fluid with lower concentration of urea;
diffusion / exchange along the whole length of surface;
2 max
(iv)    0.2 × 60 = 12 dm^3 h^-1;
(principle: volume per hour)
12 × 5 = 60 dm^3;
(correct answer 2 marks)
2
[10]

M6.          (a)     Population – organisms of one species in an ecosystem / habitat / area;
Community – organisms of all species / all populations in an
ecosystem / habitat / area;
2

(b)     (i)      No immigration / migration (Ignore references to emigration);
No reproduction (Ignore references to death);
Idea of mixing;
Marking does not influence behaviour / increase vulnerability
to predation;
Sample / population large enough;
max 2

(ii)     ; 672;
Correct answer (however derived) scores 2 marks
Incorrect answer with evidence of correct method scores 1 mark.
2
(c)     Principle of randomly placed quadrats and method of producing random
quadrats; (Reject ‘throwing’)
Valid method of obtaining no. dandelions in given area (mean per
quadrat / total no. in many quadrats);
Multiply to give estimate for total field area;
3

(d)     (i)      Niche of A – 1;
Niche of B – 3;
Too small for B / too hot for A – 4;
Too large for A / too cold for B – 2;
All four correct = 2 marks; any 2 correct = 1 mark
2

(ii)     Original population living in one area / 2 species evolved in
the area;
Idea of genetic variability;
Concept of reproductive isolation;
Possible mechanism;
Gene pools become increasingly different;
Until interbreeding does not produce fertile offspring;
max 4
[15]

M7.          (a)     Endonuclease / restriction enzyme;
1
(b)     DNA made of base pairs;
Each base pair is same length / occupies same distance
along backbone;
2

(c)     (i)      Second blank box from left labelled 6;
1
(ii)     Distance moved depends on length / number of base pairs / 
second longest fragment / second shortest distance identified;
1
(d)     5;
1
[6]

M8.          (a)     (i)      where mitosis / division / growing / occurs
(reject growing cells)
1
(ii)     to distinguish chromosomes / chromosomes not visible
without stain;
1
(iii)     to let light through / thin layer;
1

(b)     (i)      74 + 18 / 982;
= 9.4% / 9%;
2
(allow 1 mark for identifying prophase & metaphase i.e.92 or correct method using wrong figures)

(ii)     genetic differences / different types of garlic;
time of day;
chance;
age of root tip;
water availability;
temperature;
nutrient availability;
(environmental factors = 1 but cannot be awarded in addition to a named environmental factor)
2 max
[7]

 

M9.          (a)     Krebs cycle / link reaction / pyruvate to acetylcoenzyme A;
Q Accept valid alternative for any of these steps.
1

(b)     (Respiratory reactions controlled by) enzymes;
Rate decreases as less kinetic energy / fewer collisions (between substrate and active site) fewer E-S complexes formed;
2

(c)     Requires hydrogen / electrons / is reduction;
Hydrogens from reduced NAD / reduced NAD reduces (pyruvic acid) / reduced NAD oxidised;
Information may be on diagram
2

(d)     Respiring anaerobically;
(Anaerobic respiration / respiration with nitrogen) less efficient / produces less ATP;
More anaerobic respiration / more glucose / substrate must be respired to produce same amount of ATP (so more carbon dioxide produced);
3
[8]

M10.          (a)     (i)      Taxis;
Ignore references to positive and negative, and prefixes such as photo-
Accept taxes / tactic
Allow phonetic spelling
1
(ii)     Moves towards stimulus / towards light;
Direction must be correct.
1

(b)     Gravity;
Antennae involved;
Doesn’t show light is involved / doesn’t respond to light as they are
unable to see / as eyes are covered;
Accept geotaxis
3

(c)     Helps them to leave the soil / ground / reach the surface;
Disperse / produce new colonies;
Avoid competition;
2 max
[7]

M11.(a)     Light (intensity) / temperature / air movement / humidity;
1
(b)     Prevent air entering / continuous water column;
Allow answer in context of shoot, xylem or potometer.
1

(c)     Distance and time;
Reject ‘amount bubble moves’
1
Radius / diameter / area (of capillary tube);
1

(d)     (used to provide) turgidity / support / description of;
(used in) photosynthesis / (produced in) respiration;
Apparatus not sealed / ’leaks’;
2 max

(e)     (i)      Returns bubble (to start);
1
(ii)     Increases reliability (of results) / anomalous result can be identified;
Q Ignore references to validity / precision / accuracy etc.
1
[8]

M12.(a)     (i)      1.      Sex;
2.      Lifestyle;
Stress, smoking, diet etc are examples of lifestyle.
3.      Body mass;
3. Allow weight for mark point 3.
4.      Health;
Reject: height.
5.      Ethnicity;
6.      Genetic factors / family history;
2 max

(ii)     1.      Large sample / number / 410 000;
Reject: random
2.      Long time period / 8.5 / many years;
3.      Different countries / more than one country;
2

(b)     Correct answer of 209 / 209.1 = 2 marks;
Answer of 210 = one mark
Incorrect answer but multiplies by 8.5 = 1 mark;
2

(c)     Age affects risk of cancer;
Must relate to cancer not just to illness
1

(d)     1.      Correlation does not mean causal relationship;
1. Reject casual for point 1.
Reference to 'due to other factors' on its own is not enough for a mark
2.      Tea / coffee contains other substances / different amounts of caffeine / estimated intake (of tea / coffee);
3.      No control group;
4.      Only one type of cancer studied / further studies required / only one investigation / study / group;
4

(e)     (i)      1.      Treated the same;
2. Accept decaffeinated
2.      No caffeine;
2. Reject placebo.
2

(ii)     1.      Absorb different amounts;
Reject: Different body masses
2.      Broken down by enzymes / digested;
3.      Different blood volumes;
4.      Differences in metabolism;
5.      Caffeine from a different source;
1 max

(iii)    1.      Less oxygen / glucose to (cancer) cells;
'Reduces cell division' on its own should not be credited.
2.      Less carcinogens;
3.      Reduces spread of cancer (cells);
1 max
[15]

M13.(a)     1.      To show the effect of the inhibitor / drug;
2.      To show the effect of yoghurt (on its own does not affect blood
glucose);
2

(b)     1.      Food is a factor affecting blood glucose / different foods contain 
different amounts of starch / glucose / sugar / carbohydrate;
Accept converse
2.      To keep starch / fibre intake the same / similar;
Accept something in food which affects the inhibitor
2

(c)     1.      Fewer E-S complexes formed;
2.      (With inhibitor) less / no starch digested to maltose ;
Require knowledge that maltose comes from starch
3.      (So) less / no glucose from maltose;
Require knowledge that glucose comes from maltose
Accept no glucose
4.      (So) less absorption of glucose (from gut);
2 max

(d)     Suitable reason; with explanation;
Paired responses – do not mix and match
Ignore references to correlation does not prove causation, 
it could be due to other factors
Examples,
1.      Need larger sample / only 30 mice / only 15 mice in each group;
Accept small sample size
2.      Might not be representative / anomalies might have a bigger or smaller effect;
Accept mean not reliable
OR
3.      Investigation only lasted 20 days;
Experiment was not long enough
4.      Can’t see what longer term effects are;
OR
5.      Fall in blood glucose is small / numbers from graph;
6.      Mice with inhibitor still have a large rise in blood glucose / so don’t know if differences significant;
Accept differences are due to chance
OR
7.      No stats / SDs / SEs;
8.      So don’t know if differences significant;
OR
9.       Blood glucose could continue to fall;
10.     which could be harmful;
OR
11.     No group without yoghurt;
12.     So cannot compare to other groups;
2 max
[8]

M14.(a)     1.      (Some of the) light that passes through is absorbed
         by chlorophyll b;
2.      This is light of around 500 and / or around 640;
Accept any value or range between 460 and 540 and / 
or 600 and 670
2

(b)     (i)      Supports hypothesis 2 (no mark)
1.      Greater carotenoid found in sun leaves than shade leaves of beech tree;
2.      Sun leaves exposed to much brighter light than shade leaves;
OR
It supports hypothesis 2 because it does not support hypothesis 1 (no mark)
3.      Although carotenoids absorb wavelengths of light that pass through leaves;
4.      There are not more carotenoids in shade leaves;
2

(ii)     1.      Mass of pigments / carotenoids in sun and shade leaves of other trees;
2.      Position of carotenoids in leaf cells;
3.      Effect of bright light on (isolated) chlorophyll;
4.      Whether without carotenoids chlorophyll is damaged (supporting hypothesis 2) / photosynthesis is reduced (supporting hypothesis 1);
1 max
[5]

M15.(a)     1.      Thin slice/section;
2.      Put on slide in water / solution / stain;
3.      Add cover slip;
Accept: ‘between two slides’
Max 2
(b)     200 (μm);;
OR
1.      Divide image length by key length eg 64/16 = 4;
2.      Multiply by 50 eg 4 × 50;
Accept for 2 marks answers in the range of 185-217 (μm)
Max 1 mark for responses not within the range
Accept: measurements in the ranges 63-65mm and 15-17mm
2
(c)     1.      Select large number of cells / select cells at random;
Accept: > 3 for “large number”
Accept: many fields of view for ‘large number of cells’
Accept: all cells in field of view
2.      Count number of chloroplasts;
3.      Divide number of chloroplasts by number of cells;
Ignore: ‘calculate the mean’
3
[7]

M16.          (a)     Lactose intolerance in babies/babies don’t make/have lactase;
Lactose (in milk) causes colic/crying/discomfort;
Lactase breaks down lactose/milk sugar;
2 max

(b)     To avoid prejudice/bias from mother (when recording crying);
Accept for mother she/they/their
Accept to avoid mothers being concerned that their
child has lactose intolerance. Q - Reject vague ref. to fair test/avoid bias with no ref. to mothers.
1

(c)     One variable; with explanation;
Example,
Type of milk used;
So same concentration of lactose;
Same age of children;
Change in enzyme production with age;

Same age of children;
Change in milk consumption with age;
Same volume of milk (per kg baby);
So same dosage (of lactose);
Accept ref. to controlling other factors in diet
Reject time in the context of duration of investigation, given in stem
Accept e.g. time of feeding each day
Accept temperature of milk, related to action of lactase enzyme
2 max

(d)     There is a decrease in crying;
Could be other causes/symptoms of colic;
Babies might cry for reasons besides colic/might have colic and
not cry/can’t be sure they have colic, they can’t talk;
Don’t know number of babies in trial/need a larger study;
So don’t know how reliable mean is;
Standard deviation not given/spread of data;
So don’t know whether difference is significant;
Babies still crying (for 1.43 hours);
Recording by mothers might not be reliable;
Longer running study to make sure effect (of lactase) lasts;
3 max
[8]

M17.         (a)     A = envelope/membrane/phospholipid (bilayer);B = capsid / nucleocapsid / capsomere / protein;
2
(i)      (HIV is) invading cells which make new viruses;Cells release viruses into blood;
2
(ii)     Virus remains dormant/exists as provirus/exists as DNA in host DNA;
Accept virus stays in cells
1

(c)     HIV destroys T cells;More (free) viruses produced leads to fall in T-cells;(So fewer) T-cells activate B-cells/memory cells;
Reduced/no antibody production;Immune system not working properly/inability to fight infection;Opportunistic infections;
4 max
[9]

M18.          (a)     Correct answer: 1.25;
Ignore working
OR    (if wrong answer)
 / = 1 mark
125 but wrong order of magnitude = 1 mark
2

(ii)     C has myosin / thick (and actin / thin) filaments;
OR
A has only actin / thin (/ no myosin / no thick) filaments;
1 max

(b)     When contracted:
Thick & thin filaments/myosin & actin overlap more;
Interaction between myosin heads & actin / cross-links form;
Movement of myosin head;
Thin filaments / actin moved along thick filaments / myosin;
Movement of thin filaments / actin pulls Z-lines closer together;
Displacement of tropomyosin to allow interaction;
Role of Ca^2+;
Role of ATP;
Allow ref. to ‘sliding filament mechanism’ /
described if no other marks awarded
4 max

(c)     (i)      8 has DMD but 3 and 4 do not / 12 has DMD but 6 and 7
do not / neither parent has the condition but their child has;
Allow parents 3 and 4 give 8, parents 6 and 7 give 12
1
(ii)     4 AND 7;
1

(iii)     Parental genotypes:  6 = X^DY AND 7 = X^DX^d
AND
Gametes correct for candidate’s P genotypes ‒ e.g.
X^D and Y + X^D   and  X^d;
Offspring genotypes correctly derived from gametes e.g.
X^DX^D + X^DX^d + X^DY + X^dY;
Male offspring with MD correctly identified: X^dY;
Probability = 0.25 / correct for candidates offsprings genotypes;
Accept ¼ / 1 in 4 / 1:3 / 25%
NOT ‘3:1’ / ‘1:4’
4

(d)     (i)      No gene fragment G;
1
(ii)     Only one copy of gene fragment F;
Male has only one X-chromosome / is XY
(c.f. female has two / is XX);
2

(iii)     10 has only one copy of gene fragment G;
10 has only one normal X-chromosome / has one abnormal /
has only one normal allele / has one X^d / is X^DX^d / is heterozygous;
11 has two normal X-chromosomes / has 2 normal alleles /
is X^DX^D / has not got X^d / has 2 copies of (F and) G;
3

(e)     (i)      To prevent rejection / prevent antibody production vs. injected cells /
injected cells have (foreign) antigen (on surface);
1
(ii)     Shows effect of cells / not just effect of injection / not just effect of
salt solution;
1

(iii)     Only one person tested so far ‒ need more to see if similar results /
need more to see if reliable;
Need to assess if new (dystrophin positive) muscle fibres are
functional / if muscle becomes functional;
Can’t tell how widespread effect is in the muscle / sample taken
near injection site;
Need to test for harmful side effects;
Need to test if successful for other mutations of dystrophin gene;
Need to assess permanence / longevity of result/insufficient time
allowed in investigation;
(In this patient) only small response / %;
Further sensible suggestion;
4 max
[25]

M19.          (a)     less muscle / thin(ner) wall in left atrium;
1
(b)     (i)      pressure of left ventricle higher than pressure of left atrium;
1
(ii)     closing of the semi-lunar valves / pocket valves;
pressure in artery / aorta is higher than ventricle;
2
[4]

M20.          (a)     47 213;
1
(b)     (i)      there is no difference in the proportion / number of influenza cases
between the 5 vaccines;
(reject vaccinated versus no vaccinated)
1
(ii)     significant difference in proportion / number of cases of influenza
between the vaccines / the null hypothesis should be rejected;
1

(c)     sample size small;
possible differences in exposure to infection;
exposure to different strains / mutants;
possible differences in existing immunity;
possible differences in sex / age;
possible differences in socio-economic status;
2 max
[5]

M21.          (i)      for correct use of sigma;
numerator = 380 and denominator = 132;
2
2.87 to 2.9 gains 2 marks
(do not allow 2.8 or denominator = 135)
(ii)      more types of prey found on strawberries;
1
[3]

M22.         (a)     chloroplast, so cell photosynthesises and moves to optimum / best light intensity for photosynthesis;
avoids damage due to bright light;
2

(b)     (i)      2700
1
(ii)      = 27 225 000 / 27 × 10^6 = 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]

M23.          (a)     used in (aerobic) respiration / to provide energy / ATP
(and not replaced by breathing) / used up by muscle and not replaced;
(reject used up and used up and not replaced)
1
(b)     36;
1

(c)     converted back to pyruvate / glycogen / glucose / CO_2 and H_2O;
reacted with oxygen / oxidised;
(reject “breaking down” with respect to glycogen and glucose)
2

(d)     (i)      vasoconstriction / contraction of muscles in arteries / arterioles / 
arteries / arterioles close;
(reject contraction of arteries / arterioles / capillaries)
1
(ii)     supplies oxygen / glucose or removal of carbon dioxide / lactate;
so cells can respire when not contracting / breathing;
2
[7]

M24.          (a)     left ventricle;
1
(b)     (i)      (left) ventricle / heart relaxes / diastole / filling / not contracting;
1
(ii)     elastic tissue / wall;
recoils / springs back (to maintain pressure);
(“contraction / muscle causing recoil” negates second point)
2

(c)     correct answer, 666 to 667 gains 2 marks; allow 1 mark for principle;
correct time for 1 heartbeat as 90 (ms) or 630÷7 / 
60 ÷ incorrect time identified from graph;
2
(d)     correct answer, 0.03, gains 2 marks;
(allow 1 mark for correct working, 16.6 ÷ 550, if answer wrong)
2
[8]

M25.          (a)     electrons;
from chlorophyll / photolysis;
2
(b)     (i)      RuBP combines with carbon dioxide to produce 2 x GP;
1
(ii)     less used to combine with carbon dioxide / 
less used to form glycerate 3-phosphate;
1

(c)     (i)      used in photosynthesis allows detection of products;
1
(ii)     ATP and reduced NADP not formed;
GP is not being used to form RuBP / is being formed from RuBP;
2
(iii)     used in respiration / formation of starch / cellulose;
1
[8]

M26.          (a)     Tapes / string / axes laid out at right angles / grid area;
Method of obtaining random co-ordinates;
Do not allow “Use random number generator”
2

(b)     (i)      Decrease then remain constant;
From 200 cm / over 150 cm;
2
(ii)     Oxygen decreasing because soil becomes more compacted / not
replaced;
Decrease in oxygen leads to fewer aerobes surviving;
2

(c)     Anaerobic bacteria replace aerobic as oxygen decreased by aerobic bacteria;
Remove competition;
Aerobic bacteria no longer able to survive in these conditions;
3

(d)     (i)      Near the surface / in top 50 cm;
Table shows decrease with time at greater depths;
2
(ii)     Decrease;
Fewer aerobic bacteria with depth;
Oxygen concentration decreases / less oxygen at depth;
3

(e)     Probability greater than 95% / 0.95;
Results are not due to chance / results are significant;
Because bars do not overlap;
3
(f)      Plot as graph;
Draw line of best fit;
Read off appropriate value;
3
[20]

M27.          (a)     It is a measure of the concentration of a gas
(in a mixture of gases or a liquid);
1
(b)     37-38%
Accept 36 – 39

(c)     muscle contraction causes increased respiration;
increased CO_2 production lowering blood pH / lactate released
lowering blood pH;
increased heat released therefore increased temperature;
increased O_2 consumption lowering tissue PO_2;
4

(d)     haemoglobin has a lower affinity for oxygen;
more O_2 for respiration;
2
(e)     3.4 times = 2 marks
(incorrect answer in which candidate shows amount of oxygen removed at rest is 4.6 and amount removed during exercise is 15.8 = 1 mark)
2

(f)      Nearly all O_2 is transported by haemoglobin / v. little transported in plasma;
EITHER
Haemoglobin is (nearly) fully saturated with O_2 at the alveoli both at
rest and when exercising;
Therefore no (very little) further increase is possible;
OR
Haemoglobin is only 95% saturated with oxygen at the alveoli;
Therefore enriching inspired / air with oxygen will raise this to 100%;
3

(g)     increased depth / rate / pulmonary ventilation;
increase stroke volume / heart rate / Q increases blood flow rate;
arterioles [Accept artery] supplying the muscles
dilate / vasodilation / greater proportion of blood flow to the muscles;
max 3
[15]

M28.          (a)     (i)      Pattern described as constant / decrease to 04.00 / 06.00
then rising;
1
(ii)     Corresponds to ventricles contracting / systole;
1
(iii)     Less / little difference between maximum and
minimum / less variation / constant / not pulsed / smoother;
pressure in vein lower
2

(b)     (i)      The larger the molecule, the less permeable;
Over 68 000 walls not permeable;
2
(ii)     Plasma proteins / albumin and globulin too large to leave capillary;
Water lost / Increase in concentration of proteins in blood / plasma;
2
(iii)     Haemoglobin in red blood cells / 
Haemoglobin too large to pass through membrane of RBC / 
Red blood cells (containing haemoglobin) too large to pass
through wall;
1
[9]

M29.          (a)     Publicity about vaccination / better health education / risks of ‘flu epidemics;
(Accept: now free on NHS (though only since 2000) / better awareness / more commonly available)
1

(b)     (i)      1990: 26% of 7.4million = 1.92million and 2000: 64% of 7.8 million = 4.99million;
increase = 3.07 million;
2
(Correct reading of all 4 figures from graph = 1)
(Correct answer but no ‘millions’ = 1)
(Correct method resulting from wrong graph reading = 1)

(ii)     Over 50% of population being vaccinated;
But only from 2000 onwards;
(Principle of more people being vaccinated each year = 1)
2

(iii)     Different strain / type of virus each year / virus mutates;
With different antigens;
Influenza antibodies / memory cells (rapidly) destroyed / need replacing;
max 2

(c)     (Protein coat) carries antigens which stimulates B-cells / production of antibodies;
Production of memory cells;
2
[9]

M30.          (a)     (i)      Selecting the nettle plant:
Random number table avoids bias in placing of quadrat;
‘Nearest centre’ avoids bias in choosing plant to measure;
1 mark for “method avoids bias”
2
(ii)     Measuring the sixth leaf:
To allow valid comparison / so as not to introduce another variable;
Reduces / avoids influence of growth / age / light / shading;
2

(b)     Definition of range + SD / effect of outliers on range + SD;
Ranges are similar in both areas;
Suggests that variation within populations is similar;
SD smaller in area of high light intensity;
Shows that area of high light intensity is a more uniform population;
4
(c)     1.164 / 1.16 / 1.2 , however derived = 2 marks
0.83 – 0.86 / 1.1, however derived = 1 mark
Evidence of correct use of both sets of figures, but inappropriate answer = 1 mark
2
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M31.          (a)     0.1 / 0.9 (s);
1
(b)     Two marks for correct answer of 75 (beats per minute);
One mark for incorrect answer based on cardiac cycle taking 0.8 seconds;
2

(c)     (i)      Pressure in ventricle higher than pressure in atria;
1
(ii)     Prevents backflow of blood / prevents flow from ventricles to atria;
1

(d)     Increase (in stroke volume) as blood pressure increases, remains constant / plateaus; after 3 kPa / when stroke volume = 82cm^3
2
(e)     Two marks for correct answer of 80;
One mark for incorrect answer recognising that ventricle contracts once every cardiac cycle / stroke volume = 70 cm^3
2

(f)      1       Muscles (surrounding veins) contract and press on (walls of) vein and squeezes blood along veins;
2       Valves prevent backflow / ensure flow in one direction;
3       Systole / contraction of heart pumps blood (through arteries) into veins / residual arterial pressure / negative pressure in chest due to inspiration;
4       Recoil of heart muscle during diastole / after contraction;
5       Draws blood from veins into atria;
Accept sucks
6       Wide lumen little resistance / friction
6
[15]

M32.          (a)     In table:
 
D | All 3 correct = 2 marks;;
B | 2 correct = 1 mark;
C | 0 or 1 correct = 0 marks

2

(b)     (i)      myelin insulates / prevents ion movement; saltation / described 
re leaping node to node;
2
(ii)     cat has higher body temperature;
ignore references to homoiothermy’ / warm-blooded
faster diffusion of ions / faster opening of ion pores / gates / channels;
2

(c)     1       increasing stimulus (potential) causes decrease in potential
difference / rise in potential at P;
2       1 or 2 is sub-threshold / 1 or 2 does not give action potential / 3 or 4 is above threshold / 3 or 4 does give an action potential;
3       influx of Na^+ ions; (not just Na / sodium)
4       voltage-gated channels (in axon membrane) opens / opens Na^+
channels / membrane more permeable to Na^+
(NOT just Na / sodium);
5       sufficient for stimulation of adjacent region of axon therefore impulse propagated (from P to Q);
5

(d)     1       X / Acetylcholine → opening of Na^+ channels / increases
Na^+ permeability and Na^+ ion entry into Z;
2       Y / Cl^– entry - lowers potential / increases potential
difference / makes potential more negative;
3       X stimulates and Y inhibits (Z);
4       balance of impulses from X and Y determines whether Z
fires action potential / determines whether potential rises
above threshold;
4
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M33.          (a)     Given only saline;
Otherwise treated exactly the same way;
2

(b)     Ethical consideration, e.g., leads to death / suffering of mice;
Large number to improve reliability / reduce sampling error;
Number of mice related to cost / space available / animal husbandry;
2 max

(c)     Vary in shape / do not grow uniformly;
Q Allow descriptions of variation in shape.
1

(d)     7.44 and 1.74;;
7.42 and 1.72;;
(Ratio) 4.28 : 1;;
(Ratio) 4.31 : 1;;
(Percentage decrease) 76.6%;;
(Percentage decrease) 76.8%;;
Any of the answers shown gain two marks.
An answer of 23.4% or 23.2%
Percentage decrease gains one mark.
Correct method of calculating rate / ratio / percentage increase with an incorrect answer gains one mark.
2 max

(e)     Reference to Mitosis;
As chromosomes cannot attach (to spindle) / chromatids cannot separate (on spindle);
Q Do not penalise confusion between chromosomes and chromatids in second marking point
Cell division / cell cycle slows down;
Q Mitosis slows down = 2 marks
Q Mitosis stopped = 1 mark
Q Mitosis must be spelt correctly
3

(f)      (i)      (Degree of) spread / variation from the mean;
1
(ii)     Both chemicals (on their own) slow down growth / are effective;
Taxol is more effective than OGF;
Combined treatment (seems) most effective;
SD overlap for OGF with taxol and taxol (on its own) so not conclusive / could be chance / both treatments could be equally effective;
Q Ignore all references to significance
4
[15]

M34.(a)     Straight lines point to point as not possible to predict intermediate values / values between points;
1

(b)     Increases then levels / falls;
Maximum antibody production 180 units / at dose of 0.25 g per kg;
2

(c)     Two marks for correct answer of 57.14 / 57.1;;
One mark for incorrect answer in which candidate clearly divides difference in antibody production / 60 by 105;
2

(d)     Takes into account different masses of mice / allows comparison;
Accept different weights of mice.
Do not accept different size.
1

(e)     Sheep red blood cells have antigens (on their surface);
Antigens are proteins foreign to mice / are non-self;
Stimulate B cells to produce antibodies;
3

(f)     Response only observed in mice;
Disease organisms not investigated;
Not all disease caused by pathogens / cured by antibodies;
i.e. not tested on humans
2 max
[11]

M35.(a)     1.      No oxygen can enter;
2.      Ethanol produced during anaerobic respiration;
OR
3.      No ethanol / carbon dioxide can escape;
4.      Allows accuracy of measuring;

OR
5.      To prevent entry of / contamination with microorganisms;
6.      Prevent competition with yeast;
Any two pairs of answers
Second mark of each pair must be related to the first point of the pair.
4 max

(b)     1.      Yeast respiring aerobically;
2.      Oxygen used equal to carbon dioxide produced;
2

(c)     1.      7.0 / 7;
2.      Ethanol production starts;
2

(d)     (i)      1.      Repeat;
2.      Identify anomalies / see if results are similar / enough results for statistical test / give more reliable mean;
3.      Carry out statistical test / statistical analysis;
4.      Ensure results are significant / find probability of results being due to chance;
5.      Peer review;
6.      Allows procedure to be checked / see if other scientists get similar results;
Two pairs of linked points, each pair a suggestion and an explanation. The explanation must relate to the suggestion to gain the second point of the pair.
4

(ii)     1.      Curve levelling off / rate of increase is decreasing / very little extra ethanol produced;
2.      Becomes less cost effective / less profit;
2. Accept a description of cost effectiveness
2

(iii)    1.      (Funding agency) might want particular results;
2.      Results may be withheld / results may not be published / results may be confidential;
2 max
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