2025 OCR GCSE Twenty First Century Science - Biology B - J257 Practice Paper with Answers

Mode = most common value = 0.19 s (appears twice), so true. Ordered values: 0.19, 0.19, 0.21, 0.22, 0.24, so the median is 0.21 s, not 0.22 s: false. Range = 0.24 - 0.19 = 0.05 s: true.

All three rows correct = 1.5 marks (AO2.1). Two rows correct = 1 mark. One row correct = 0.5 marks. Correct answers: mode True; median False; range True.

Algae make their own food by photosynthesis, so they are producers. The snail eats the producer, so it is a primary consumer. The heron is at the end of the chain and is eaten by nothing in it, so it is the top predator (the third consumer). Decomposer is a spare description.

Algae–A, water snail–B, heron–C. All three correct = 1.5 marks; two correct = 1 mark; one correct = 0.5 marks (AO1.1). DO NOT ALLOW more than one line from an organism.

Water moves into root cells from the soil by osmosis through the root hair cells, which have a large surface area. Nitrate ions are needed to make amino acids and so proteins.

osmosis (0.5); root hairs (0.5); nitrate (0.5) (AO1.1). Total 1.5 marks. DO NOT ALLOW glucose for nitrate.

A correlation shows a link, not proof of cause (B is wrong). A larger sample improves reliability (C). Other factors may affect the outcome (E). D is wrong because risk factors only raise the chance of disease.

A, C, E ticked. 0.5 marks for each correct tick (AO2.1). If more than three boxes are ticked, subtract 0.5 for each extra tick, to a minimum of 0.

Asexual reproduction involves one parent and mitosis, giving clones. Fertilisation is the fusion of gametes in sexual reproduction, which mixes genes from two parents and so gives more variation.

Row 1 Asexual; row 2 Sexual; row 3 Sexual. All correct = 1.5 marks; two correct = 1 mark; one correct = 0.5 marks (AO1.1).

Communicable diseases are caused by pathogens that can pass between people or from animals. Cholera (bacterium), malaria (protist) and TB (bacterium) are communicable. Diabetes, lung cancer and heart disease are non-communicable.

Cholera, malaria, TB ticked: 0.5 marks each (AO1.1). Subtract 0.5 for each extra tick, minimum 0.

Mitochondria release energy by aerobic respiration. Ribosomes join amino acids to make proteins. The cell membrane is partially permeable and controls what moves in and out. D describes the nucleus and is spare.

1–C, 2–B, 3–A. All correct = 1.5 marks; two correct = 1 mark; one correct = 0.5 marks (AO1.1).

The receptor detects the stimulus, the sensory neurone carries the impulse to the spinal cord, the relay neurone passes it to the motor neurone, which carries it to the effector (muscle), which contracts.

B, E, D, A, C. All four remaining letters in correct positions = 1.5 marks; three correct positions = 1 mark; two correct positions = 0.5 marks (AO1.1).

Row 1: 25 cm is greater than 12 cm, so supported. Row 2: only one soil type was tested, so the claim goes beyond the data. Row 3: 24 cm is less than 25 cm, so supported.

Row 1 Supported (0.5, AO3.2a)
Row 2 Not supported (0.5, AO3.2a)
Row 3 Supported (0.5, AO3.2a)
Guidance: all three correct = 1.5 marks; award 0.5 per correct row. DO NOT ALLOW more than one tick in a row.

Pondweed photosynthesises so it is the producer. The snail eats the producer (primary consumer), so the stickleback eating the snail is the secondary consumer. Heat loss is loss of energy.

producer (0.5, AO1.1)
secondary consumer (0.5, AO2.1)
energy (0.5, AO1.1)
Guidance: ALLOW 'second consumer'. DO NOT ALLOW 'primary consumer' or 'tertiary consumer' for the second blank.

Root hair cells have a large surface area for absorption. Stomata let CO2 diffuse in. Xylem transports water and minerals upward. Function 4 is a spare.

A–3 (0.5, AO1.1)
B–1 (0.5, AO1.1)
C–2 (0.5, AO1.1)
Guidance: all three correct = 1.5; award 0.5 per correct link. Two links from one structure = no mark for that structure.

Saturated fat raises cholesterol and causes fatty deposits in arteries; smoking damages artery walls; high blood pressure damages vessels and strains the heart. Exercise and fruit and vegetables lower the risk; measles vaccination is unrelated.

Diet high in saturated fat (0.5, AO1.1)
Smoking cigarettes (0.5, AO1.1)
High blood pressure (0.5, AO1.1)
Guidance: each extra tick above three cancels one correct mark (minimum 0).

Asexual reproduction involves one parent and mitosis, giving clones. Sexual reproduction involves fusion of gametes and mixing of genes, giving variation.

Row 1 Asexual (0.5, AO1.1)
Row 2 Sexual (0.5, AO1.1)
Row 3 Sexual (0.5, AO1.2)
Guidance: 0.5 per correct row.

Diseases that spread between people are communicable. Cystic fibrosis is passed on through genes, so is inherited. Tuberculosis is a bacterial disease, so antibiotics are effective.

communicable (0.5, AO1.1)
inherited (0.5, AO1.1)
bacteria (0.5, AO1.1)
Guidance: ALLOW 'bacterium' / 'bacterial'. DO NOT ALLOW 'non-communicable' for the second blank as the sentence reads 'an ........ disorder'.

Mitochondria release energy by aerobic respiration, ribosomes make proteins, and the nucleus holds DNA. Photosynthesis happens in chloroplasts, so 4 is a spare.

A–3 (0.5, AO1.1)
B–2 (0.5, AO1.1)
C–1 (0.5, AO1.1)
Guidance: 0.5 per correct link.

Receptor detects the stimulus (B), the sensory neuron carries the impulse to the spinal cord (D), the relay neuron passes it to the motor neuron (A), and the muscle effector contracts (C).

D second (0.5, AO1.2)
A third (0.5, AO1.2)
C last (0.5, AO1.2)
Guidance: ECF allowed for correct relative order of remaining letters; 0.5 per letter in the correct position.

The scatter diagram shows more sunshine goes with more cases, which is a positive correlation. A correlation alone does not show cause, so row 2 is not supported. Row 3 is the opposite of the pattern.

All three rows correct = 1.5 marks (AO3.1a). Two rows correct = 1 mark. One row correct = 0.5 mark. Row 1 Supported; row 2 Not supported; row 3 Not supported. DO NOT ALLOW two ticks in one row.

Plants use carbon dioxide in photosynthesis to make glucose. Decomposers break down dead material and release carbon dioxide through respiration.

All four correct = 1.5 marks (AO1.1). Three correct = 1 mark. Two correct = 0.5 mark. Fewer than two = 0. DO NOT ALLOW 'carbon dioxide' for gap 2 or 'respiration' for gap 1.

Nitrate supplies nitrogen for amino acids and proteins. Magnesium is needed for chlorophyll. Phosphate is used in DNA and membranes.

Three correct lines = 1.5 marks (AO1.1). Two correct = 1 mark. One correct = 0.5 mark. DO NOT ALLOW more than one line from a mineral ion.

Saturated fat raises blood cholesterol and smoking damages artery walls and raises blood pressure. The other options are not risk factors.

Both correct boxes ticked = 1.5 marks (AO1.1). One correct box and no incorrect box = 0.75 marks. Ticking more than two boxes: deduct 0.75 for each incorrect tick beyond two (minimum 0).

Asexual reproduction involves one parent and produces clones. Sexual reproduction involves fusion of gametes and mixes alleles, increasing variation.

All three rows correct = 1.5 marks (AO1.1). Two rows correct = 1 mark. One row correct = 0.5 mark. DO NOT ALLOW two ticks in one row.

Malaria is caused by a protist carried by mosquitoes. Rose black spot is a fungal disease of plants. Measles is caused by a virus.

Three correct lines = 1.5 marks (AO1.1). Two correct = 1 mark. One correct = 0.5 mark. DO NOT ALLOW more than one line from a disease.

Aerobic respiration happens in mitochondria, proteins are made at ribosomes, and chloroplasts contain chlorophyll that absorbs light.

Three correct lines = 1.5 marks (AO1.1). Two correct = 1 mark. One correct = 0.5 mark. DO NOT ALLOW more than one line from an organelle.

The receptor detects the stimulus (B), the sensory neuron carries the impulse to the spinal cord (D), the relay neuron passes it to the motor neuron (A), and the effector muscle contracts (C).

B, D, A, C in that order = 1.5 marks (AO1.1). Two of the three boxes in the correct position = 1 mark. One of the three boxes in the correct position = 0.5 mark.

The heart rate rises steadily from 64 to 82 beats per minute as volume rises, so statements 1 and 3 are supported. The data show a correlation only; other factors were not controlled or tested, so statement 2 cannot be concluded.

All three rows correct = 1.5 marks (AO3.2b)
Two rows correct = 1 mark
One row correct = 0.5 marks
Guidance: a correlation does not prove causation (AO3).

Waterweed makes food by photosynthesis so is the producer. The snail eats the producer (primary consumer), the stickleback eats the snail (secondary consumer), and the heron eats the stickleback (tertiary consumer).

producer = 0.5 mark (AO1.1)
secondary consumer = 0.5 mark (AO2.1)
tertiary consumer = 0.5 mark (AO2.1)
Guidance: DO NOT ALLOW 'consumer' alone for the last two blanks as it is not specific enough.

Nitrate supplies nitrogen for amino acids and proteins. Magnesium is a component of chlorophyll. Phosphate is needed for DNA and membranes.

All three lines correct = 1.5 marks (AO1.1)
Two correct = 1 mark
One correct = 0.5 marks
Guidance: more than one line from a mineral ion = that line is not credited.

Saturated fat raises cholesterol and causes fatty deposits in arteries; smoking damages artery walls; high blood pressure damages vessels. Exercise and fruit and vegetables lower risk; blood group is not a recognised risk factor.

All three correct and no others = 1.5 marks (AO1.1)
Two correct and no incorrect = 1 mark; or three correct with one incorrect extra tick = 1 mark
One correct = 0.5 marks
Guidance: more than three ticks, award marks for correct ticks minus incorrect ticks.

Asexual reproduction uses mitosis and produces clones. Gametes are made by meiosis only in sexual reproduction, and fusion of gametes gives genetic variation.

All three rows correct = 1.5 marks (AO1.1)
Two rows correct = 1 mark
One row correct = 0.5 marks

Athlete's foot is caused by a fungus, malaria by a protist carried by mosquitoes, and Salmonella food poisoning by a bacterium. Virus is a spare answer.

All three lines correct = 1.5 marks (AO1.1)
Two correct = 1 mark
One correct = 0.5 marks

Mitochondria are the site of aerobic respiration, ribosomes make proteins, and chloroplasts contain chlorophyll for photosynthesis.

mitochondria = 0.5 mark
ribosomes = 0.5 mark
chloroplast = 0.5 mark (AO1.1)
Guidance: ALLOW 'mitochondrion' and 'chloroplasts'.

The receptor detects the stimulus, the sensory neurone carries the impulse to the spinal cord, the relay neurone connects to the motor neurone, the motor neurone carries the impulse to the effector, and the muscle contracts.

B D A E C all correct = 1.5 marks (AO1.1)
Two or three of D, A, E, C in the correct position = 1 mark
One in the correct position = 0.5 marks
Guidance: ECF allowed for relative order of correct pairs.

Water moves into root hair cells from a dilute solution (soil) to a more concentrated one across a partially permeable membrane: osmosis. Nitrate ions provide nitrogen for amino acids and proteins. Mineral ions are usually at a lower concentration in the soil than in the root hair cell, so they are moved against the gradient using energy: active transport.

1. osmosis (0.5) AO1.1
2. nitrate (0.5) AO1.1
3. active transport (0.5) AO1.1
DO NOT ALLOW phosphate for 2 (it is needed for DNA/ATP, not amino acids). Total 1.5 marks; if more than one word is written on a line for that line, award 0.

Sensory neurons carry impulses towards the CNS, so row 1 is true. Reflexes are rapid and automatic and do not involve conscious thought, so they are faster than voluntary actions and row 2 is false. At a synapse a transmitter chemical diffuses across the gap, so row 3 is true.

Row 1: True (0.5) AO1.1
Row 2: False (0.5) AO1.1
Row 3: True (0.5) AO1.1
More than one tick in a row = 0 for that row. Total 1.5 marks.

Mitochondria are the site of aerobic respiration (C). Ribosomes make proteins during protein synthesis (A). Chloroplasts contain chlorophyll and are where photosynthesis takes place (B). D describes the cell membrane and is not needed.

Mitochondria to C (0.5) AO1.1
Ribosome to A (0.5) AO1.1
Chloroplast to B (0.5) AO1.1
If more than one line is drawn from a structure, award 0 for that structure. Total 1.5 marks.

Plants absorb nitrate ions from the soil. Nitrates provide nitrogen needed to make amino acids, which are joined to make proteins used for new cells and growth. Nitrogen is also needed for chlorophyll, so a shortage causes yellow leaves.

0.5 mark each, any three from:
- nitrate ions are a source of nitrogen / needed to make amino acids (AO1.1)
- amino acids are used to make proteins (AO1.1)
- proteins are needed for growth / new cells / enzymes (AO2.1)
- (nitrogen needed to make) chlorophyll, so less photosynthesis (AO2.1)
ALLOW 'protein synthesis'. IGNORE 'nitrates are plant food'.

Small fish eat water fleas, so with no small fish fewer water fleas are eaten and their numbers rise. More water fleas eat more algae, so algae numbers fall.

- water fleas increase (0.5) (AO2.1)
- because fewer are eaten / no predators (0.5) (AO2.1)
- algae decrease because more are eaten by (more) water fleas (0.5) (AO2.2)
ALLOW 'go up'/'go down'. IGNORE any answer about the heron only.

Break the transmission route: keep sewage away from drinking water, treat water, boil it, and improve hygiene so bacteria are not passed on.

0.5 mark each, any three from:
- treat / purify / chlorinate drinking water
- boil water before drinking
- separate sewage from drinking water / proper sewage disposal
- wash hands (with soap) before eating / after toilet
- vaccinate people
- isolate / treat infected people
IGNORE 'keep clean' without detail. (AO1.2 / AO2.1)

Electron microscopes use beams of electrons, giving much greater magnification and resolving power, so sub-cellular structures like ribosomes and the detailed structure of mitochondria are visible.

0.5 mark each, any three from:
- greater magnification
- greater resolution / clearer detail
- can see sub-cellular structures / ribosomes / internal structure of mitochondria
- (image is) black and white / not natural colour
- specimen must be dead / in a vacuum
DO NOT ALLOW 'bigger cells'. (AO1.1)

A reflex is an automatic, fast response, travelling via a reflex arc (sensory neuron, relay neuron in the spinal cord, motor neuron) without waiting for conscious decision. The speed reduces tissue damage.

- automatic / involuntary / no conscious thought (0.5) (AO1.1)
- fast / rapid response (0.5) (AO1.1)
- protects from harm / prevents burns / damage (0.5) (AO2.1)
ALLOW 'does not involve the brain'.

Mitosis copies the chromosomes and then divides to give two cells with the same genetic information and chromosome number as the parent. Gametes are made by meiosis.

(a) genetically identical / same DNA / clones (0.5); same number of chromosomes (0.5) (AO1.1)
(b) meiosis (0.5) (AO1.1)
DO NOT ALLOW 'mitosis' for (b).

A correlation does not show cause. People who eat more vegetables may also exercise more or eat less salt. These uncontrolled variables could be the real cause.

- it shows a correlation / link / association only (0.5) (AO3.2b)
- other factors / variables not controlled (0.5) (AO3.2b)
- named example e.g. exercise / salt / smoking / age / weight (0.5) (AO2.2)
IGNORE 'sample too small'.

In sexual reproduction two parents contribute genes through gametes that differ from each other, and random fertilisation produces new combinations. Asexual reproduction copies one parent's DNA, so offspring are identical apart from mutation.

- two parents / genes from both parents (0.5) (AO1.1)
- gametes genetically different / meiosis mixes genes (0.5) (AO1.1)
- random fertilisation gives new combinations of alleles (0.5) (AO2.1)
ALLOW ORA for asexual (clones / identical to parent). IGNORE mutation alone.

Diffusion only moves particles down a concentration gradient. Soil mineral ions are at a lower concentration than inside the root hair cell, so they must be moved in against the gradient. This requires energy released by respiration.

- ions at lower concentration in soil than in the cell (0.5) (AO2.1)
- movement is against the concentration gradient (0.5) (AO1.1)
- requires energy / from respiration / ATP (0.5) (AO1.1)
IGNORE 'carriers' alone.

As sleep increases, reaction time decreases, so the correlation is negative. A correlation only shows a link; other variables were not controlled, so cause is not proven.

Negative (correlation) (0.5) AO2.1
Correlation does not show / prove cause (0.5) AO1.2
Other variable(s) could affect reaction time / not controlled, e.g. caffeine, age (0.5) AO3.2b
IGNORE 'inverse' alone. DO NOT ALLOW 'positive'.

Fewer sticklebacks means less predation on snails, so snail numbers rise. Herons have less food, so their numbers fall.

Snails increase / go up (0.5) AO2.1
because fewer predators / less eaten by sticklebacks (0.5) AO2.1
Herons decrease because less food / fewer sticklebacks to eat (0.5) AO2.1
ALLOW ECF if both directions reversed consistently with reasoning. IGNORE 'die' without reason.

Magnesium ions are absorbed by roots and used to make chlorophyll. Without enough, leaves are yellow, absorb less light, photosynthesise less and make less glucose for growth.

Magnesium needed to make chlorophyll (0.5) AO1.1
Less light absorbed / less photosynthesis (0.5) AO2.1
Less glucose / carbohydrate / biomass made for growth (0.5) AO2.1
IGNORE 'magnesium is a food'.

Fat deposits narrow the coronary arteries, restricting blood flow. A blockage stops oxygen and glucose reaching heart muscle, causing a heart attack.

Fatty deposits / cholesterol build up in (coronary) arteries (0.5) AO1.1
Arteries narrowed / blocked, (blood clot) (0.5) AO1.1
Less oxygen / glucose reaches heart muscle (so cells cannot respire) (0.5) AO2.1
DO NOT ALLOW veins. IGNORE 'heart blocked'.

Asexual reproduction produces clones. This keeps good traits but gives no variation, so a disease can affect all plants.

Advantage: offspring genetically identical / clones (0.5) so keep desired characteristics (0.5) AO1.1
Disadvantage: no variation so all (equally) susceptible to the disease / none may be resistant (0.5) AO2.1
ALLOW AW. IGNORE 'faster' alone.

Communicable diseases are caused by pathogens that can spread between individuals. Cholera spreads in water contaminated with faeces.

Disease caused by pathogen / microorganism (0.5) AO1.1
Can be passed / spread between people / organisms (0.5) AO1.1
Contaminated water / food (0.5) AO1.2
IGNORE 'catching it' alone. DO NOT ALLOW 'air' or 'touch' only.

Mitochondria release energy by aerobic respiration. Liver cells carry out many energy-demanding reactions, so need many mitochondria.

Site of (aerobic) respiration (0.5) AO1.1
releases energy / makes ATP (0.5) AO1.1
Liver cells are very active / need lots of energy (for metabolic reactions) (0.5) AO2.1
DO NOT ALLOW 'makes / produces energy'. IGNORE 'powerhouse'.

The receptor detects heat and sends impulses along a sensory neurone to the relay neurone in the spinal cord. Impulses pass via a synapse to a motor neurone, then to the muscle, which contracts.

Sensory neurone carries impulse from receptor (to CNS / spinal cord) (0.5) AO1.1
Relay neurone in CNS / spinal cord, impulses cross synapse(s) (0.5) AO1.1
Motor neurone to effector / muscle (0.5) AO1.1
ALLOW intermediate neurone. Order must be correct.

The student changes temperature (independent) and measures bubbles per minute (dependent). Light intensity, CO2 concentration or pondweed size must be kept the same.

Independent variable: temperature (0.5) AO2.2
Dependent variable: number of bubbles (in one minute) / rate of oxygen production (0.5) AO2.2
One control: light intensity / distance of lamp / CO2 concentration / same pondweed / time (0.5) AO3.3a
IGNORE 'same amount of water' unqualified.

The value 190 is much higher than the others, so it is anomalous. Remaining values: 128 + 135 + 131 + 136 = 530. Mean = 530 / 4 = 132.5, which is 133 to the nearest whole number.

190 identified as anomalous (0.5)
Adds the four remaining values / divides by 4 (0.5)
133 (bpm) (0.5)
ALLOW 132.5 for the method marks. ECF if a different anomaly is chosen and the mean is correctly calculated. AO2.1 / AO3.1a

With fewer sticklebacks, fewer snails are eaten so the snail population rises. More snails eat more algae, so the algae population falls.

Water snail numbers increase (0.5) because fewer are eaten / less predation by sticklebacks (0.5)
Algae numbers decrease because more snails are eating them (0.5)
IGNORE references to herons. AW. AO2.1

Moving ions against a concentration gradient is active transport. This needs energy, which mitochondria supply through aerobic respiration.

Active transport (0.5)
It needs energy / ATP (0.5)
Mitochondria release energy / are the site of (aerobic) respiration (0.5)
DO NOT ALLOW 'produce' or 'make' energy. DO NOT ALLOW diffusion or osmosis. AO1.1 / AO2.1

The data shows a correlation. A correlation does not prove one factor causes the other, because other variables such as stress or work patterns could affect both coffee drinking and sleep.

Correlation (0.5)
Any two from:
A correlation does not show cause (0.5)
Other factors / a named factor (e.g. stress, work hours) may affect both (0.5)
Sample size small / not representative (0.5)
Max 1.5. AO3.2b

Seeds come from gametes that combine, giving offspring that differ genetically. Some may be resistant to the fungus, survive, and pass on resistance, whereas asexual offspring are all clones and equally vulnerable.

Sexual reproduction produces variation / offspring that are genetically different (0.5)
Some plants may be resistant to the disease (0.5)
These survive and reproduce / pass on the allele (0.5)
ORA for asexual clones. AO2.1

Communicable diseases are caused by pathogens that spread between individuals. Cholera spreads through contaminated water, so clean water and sewage treatment reduce transmission.

Can be passed on / spread from one person to another (caused by a pathogen) (0.5)
Any two from: clean / treated drinking water; sewage treatment / separating sewage from water; handwashing / good hygiene; vaccination; cooking food thoroughly (0.5 each)
IGNORE 'medicine' alone. AO1.1 / AO2.1

Ribosomes are too small to be seen clearly with a light microscope. Electron microscopes have a higher resolving power so can show them. Ribosomes are where amino acids are joined to make proteins.

Higher resolution / resolving power (0.5)
Ribosomes are too small to be seen with a light microscope / need higher magnification (0.5)
Ribosomes make / synthesise protein (0.5)
DO NOT ALLOW 'clearer' alone. AO1.1 / AO1.2

The response is automatic and rapid, so it is a reflex. The impulse travels along the sensory neurone to the relay neurone in the spinal cord, then along the motor neurone to the muscle, which contracts.

Reflex (action) (0.5)
Sensory neurone to relay neurone / spinal cord / CNS (0.5)
Motor neurone to muscle / effector (0.5)
DO NOT ALLOW 'nerve' for neurone if the order is unclear. AO1.1

Rearrange: real size = image size ÷ magnification.
real length = \( 45 \div 300 = 0.15 \) mm.

First check the answer on the answer line. If answer = 0.15 (mm) award 2 marks.
1 mark: correct rearrangement/substitution, \( 45 \div 300 \) (AO2.1).
1 mark: 0.15 (AO2.1).
ALLOW 0.150. ALLOW 150 µm (units must be correct if given in µm). ECF for a wrong rearrangement giving 1 mark for method only. DO NOT ALLOW 13500 (45 × 300) for the answer mark.

Mean per quadrat = \( (6+3+5+2+4) \div 5 = 20 \div 5 = 4 \) per m².
Estimated total = \( 4 \times 400 = 1600 \).

First check the answer on the answer line. If answer = 1600 award 2 marks.
1 mark: calculates mean = 4 (per m²) (AO2.1).
1 mark: \( 4 \times 400 = 1600 \) (AO2.1).
ALLOW ECF from an incorrect mean multiplied by 400 for the second mark. DO NOT ALLOW 4 on its own as the final answer.

Change in mass = \( 4.2 - 5.0 = -0.8 \) g.
Percentage change = \( (-0.8 \div 5.0) \times 100 = -16\% \).

First check the answer on the answer line. If answer = -16 / 16 decrease award 2 marks.
1 mark: change in mass = 0.8 (g) and divided by 5.0, i.e. \( 0.8 \div 5.0 \times 100 \) (AO2.1).
1 mark: 16 (%) with a decrease shown by minus sign or the word decrease/loss (AO2.1).
ALLOW 16 for 2 marks if the answer line or working clearly shows a decrease. If no indication of a decrease, award 1 mark. DO NOT ALLOW 19 (dividing by 4.2) for the answer mark; ALLOW 1 mark for \( 0.8 \div 4.2 \times 100 \) only if method is clear (ECF).

Find 60 on the x-axis. Move up to 17 on the y-axis. Mark a small cross or dot at (60, 17).

Point plotted at (60, 17) correctly = 1 mark (AO2.2). ALLOW a plot within half a small square of the correct position. DO NOT ALLOW a large blob covering more than one small square. IGNORE a line joining points.

Draw one continuous, smooth line that follows the trend of the points: it rises slowly, then steeply between years 1 and 3, then levels off towards 150 at years 4 and 5.

Smooth curve of best fit passing through or close to all plotted points = 1 mark (AO2.2). DO NOT ALLOW straight lines ruled between points (dot-to-dot), a thick or double line, or a curve that does not follow the trend. IGNORE extending the line slightly beyond the first or last point.

A weak positive correlation shows a general tendency only. Correlation does not prove causation, and 'every' is too strong for a weak correlation.

Row 1 valid = 0.5 (AO3.2b)
Row 2 not valid = 0.5 (AO3.2b)
Row 3 not valid = 0.5 (AO3.2b)
More than one box ticked in a row = 0 for that row.

Algae photosynthesise so are producers. The snail eats the algae so is the primary consumer. The perch eats the snail so is its predator.

producer = 0.5 (AO1.1)
primary consumer = 0.5 (AO2.1)
predator = 0.5 (AO2.1)
DO NOT ALLOW secondary consumer for the second gap.

Root hair cells have a large surface area for absorbing water and mineral ions. Stomata allow carbon dioxide to diffuse into the leaf. Xylem carries water up the stem.

Root hair cell – water and mineral ions = 0.5 (AO1.1)
Stoma – carbon dioxide = 0.5 (AO1.1)
Xylem vessel – water transported up the stem = 0.5 (AO1.1)
IGNORE a line from phloem unless it replaces a correct link. More than one line from a structure = 0 for that structure.

Diet is a choice, so lifestyle. Air pollution comes from surroundings, so environmental. A faulty allele is passed on in genes, so inherited.

Diet = lifestyle 0.5 (AO1.1)
Traffic fumes = environmental 0.5 (AO1.1)
Faulty allele = inherited 0.5 (AO1.1)
More than one tick in a row = 0 for that row.

Asexual reproduction uses mitosis and produces clones. Sexual reproduction involves fusion of gametes and produces variation, which helps some offspring survive changes such as a new disease.

Row 1 asexual = 0.5 (AO1.1)
Row 2 sexual = 0.5 (AO1.1)
Row 3 sexual = 0.5 (AO2.1)
More than one tick in a row = 0 for that row.

Malaria pathogens are protists. A mosquito carrying a pathogen is a vector. Tuberculosis is a bacterial disease, so antibiotics can treat it.

protists = 0.5 (AO1.1)
vector = 0.5 (AO1.1)
bacteria = 0.5 (AO1.1)
DO NOT ALLOW viruses for the third gap, since antibiotics do not work on viruses.

Mitochondria release energy by aerobic respiration, the nucleus contains the genetic material controlling the cell, and ribosomes make proteins.

Mitochondrion – aerobic respiration = 0.5 (AO1.1)
Nucleus – controls the activities of the cell = 0.5 (AO1.1)
Ribosome – protein synthesis = 0.5 (AO1.1)
IGNORE a line from the cell membrane unless it replaces a correct link.

95 mm is far from the other values, so it is an anomaly. Mean of all five = 335 ÷ 5 = 67 mm, not 60 mm (60 is the mean excluding the anomaly: 240 ÷ 4). Ordered values: 58, 59, 61, 62, 95, so the median is 61 mm.

Row 1 correct = 0.5 (AO3.2b)
Row 2 not correct = 0.5 (AO2.2)
Row 3 correct = 0.5 (AO2.2)
More than one tick in a row = 0 for that row.

The heart rate rises as volume rises, so there is a positive correlation (A). With only five volunteers, a larger sample would make the conclusion more reliable (D). B claims causation for every person, which five results cannot show. C is the opposite of the pattern. E is not supported by the data.

A ticked
D ticked
AO3.2b
Both correct = 1.5 marks; one correct tick with no incorrect ticks = 0.5 marks. Deduct 0.5 for each extra tick; total not below 0.

Pondweed makes food by photosynthesis so it is the producer. The snail eats the producer so it is a primary consumer. The stickleback is the secondary consumer, so the heron, at the fourth level, is the tertiary consumer.

producer (0.5)
primary consumer (0.5)
tertiary consumer (0.5)
AO1.1
DO NOT ALLOW 'secondary consumer' for the heron.

Nitrate supplies nitrogen for amino acids and proteins. Magnesium is a part of the chlorophyll molecule. Water keeps cells turgid and is a reactant in photosynthesis.

1-B (0.5)
2-A (0.5)
3-C (0.5)
AO1.1
IGNORE extra lines/letters if the intended match is clear; two links to one item from one number = no mark for that row.

The study shows a link (correlation), which is statement 1. A correlation does not prove cause for everyone, so statement 2 is not supported. Other risk factors such as smoking, obesity, genes and exercise could also affect the risk, so statement 3 is reasonable.

Row 1 Supported (0.5)
Row 2 Not supported (0.5)
Row 3 Supported (0.5)
AO3.2b
All three correct = 1.5; two correct = 1; one correct = 0.5.

Asexual reproduction involves mitosis in one parent, giving clones. Fertilisation is the fusion of gametes in sexual reproduction. Mixing of genes from two parents gives more variation.

Row 1 Asexual (0.5)
Row 2 Sexual (0.5)
Row 3 Sexual (0.5)
AO1.1
All correct = 1.5; two correct = 1; one correct = 0.5.

Cholera (bacterium), tuberculosis (bacterium) and athlete's foot (fungus) are caused by pathogens and can be passed between people. Type 1 diabetes, lung cancer and cystic fibrosis are non-communicable.

A (0.5)
C (0.5)
E (0.5)
AO1.1
Deduct 0.5 for each incorrect extra tick; total not below 0.

Mitochondria are the site of aerobic respiration, ribosomes make proteins and chloroplasts carry out photosynthesis. D describes the cell membrane and is a spare.

1-B (0.5)
2-A (0.5)
3-C (0.5)
AO1.1
DO NOT ALLOW D for any row.

The glucose moves from low to high concentration, which is against the concentration gradient. This needs energy from respiration, so it is active transport.

C ticked (1.5)
AO2.1
More than one tick = 0.

The data show that earthworm number rises as soil moisture rises, so a positive correlation and a higher number at wetter sites are supported. The data alone cannot show that wet soil causes earthworms to be produced, because correlation does not prove causation.

All three rows correct = 1.5 marks. Two rows correct = 1 mark. One row correct = 0.5 marks. Zero correct = 0. AO3.2b. DO NOT ALLOW more than one tick in a row.

Pondweed photosynthesises, so it is the producer. Fewer perch means fewer dragonfly larvae are eaten, so larva numbers increase at first.

(a) pondweed = 0.75 mark. (b) Their numbers increase = 0.75 mark. AO1.1 for (a), AO2.1 for (b). DO NOT ALLOW more than one tick per part.

Root hair cells have a large surface area for water and mineral uptake. Stomata let carbon dioxide diffuse into leaves. Xylem transports water upwards.

3 correct links = 1.5 marks; 2 correct = 1 mark; 1 correct = 0.5 marks. AO1.1. DO NOT ALLOW more than one line from a structure.

A high saturated fat diet raises blood cholesterol and smoking damages artery walls; both increase risk of cardiovascular disease.

Each correct box = 0.75 mark, maximum 1.5. If more than two boxes are ticked, subtract 0.75 per extra tick (minimum 0). AO1.1.

Gametes fuse at fertilisation and are made by meiosis, which shuffles alleles. Offspring therefore differ genetically from their parents, increasing variation.

Each correct word = 0.5 mark. gametes; meiosis; different. AO1.1. DO NOT ALLOW mitosis.

Measles (virus) and salmonella (bacteria) are caused by pathogens that can pass between people. Type 1 diabetes is not caused by a pathogen and cannot be passed on.

All three correct = 1.5; two correct = 1; one correct = 0.5. AO1.1. DO NOT ALLOW two ticks in a row.

Mitochondria release energy by aerobic respiration, ribosomes make proteins, and the nucleus holds the chromosomes.

3 correct links = 1.5 marks; 2 correct = 1 mark; 1 correct = 0.5 marks. AO1.1.

Stimulus detected by receptor (B), sensory neuron (E), relay neuron (C), motor neuron (A), effector muscle contracts (D).

E, C, A in the three boxes in that order = 1.5 marks. Two of three boxes correct = 1 mark. One of three correct = 0.5 marks. AO1.2.

Mitochondria are the site of aerobic respiration, which releases energy from glucose. Chloroplasts contain chlorophyll, which absorbs light for photosynthesis. The cell membrane controls the movement of substances into and out of the cell. Function D (genetic material) describes the nucleus, so it is a spare.

Mitochondrion to B (AO1.1) 1 mark
Chloroplast to C (AO1.1) 0.5 mark
Cell membrane to A (AO1.1) 0.5 mark
All three correct = 1.5 marks; two correct = 1 mark; one correct = 0.5 mark.
DO NOT ALLOW more than one line from a structure (that link scores no mark).
Guidance: D is a distractor (nucleus).

Movement against a concentration gradient using energy is active transport. Root hair cells have a large surface area for absorbing ions and water. Xylem carries water and mineral ions upwards from the roots.

active transport (AO1.1) 0.5 mark
root hair cells (AO1.1) 0.5 mark
xylem (AO1.1) 0.5 mark
Mark each gap in position.
DO NOT ALLOW diffusion for the first gap (contradicts 'against the concentration gradient').
DO NOT ALLOW phloem for the third gap.

The study shows a correlation between processed meat intake and bowel cancer risk. A correlation does not prove that one factor causes the other, and it cannot show that it affects everyone or that no other factors matter.

Row 1 correct conclusion (AO3.2b) 0.5 mark
Row 2 not a correct conclusion (AO3.2b) 0.5 mark
Row 3 not a correct conclusion (AO3.2b) 0.5 mark
All three correct = 1.5 marks; two correct = 1 mark; one correct = 0.5 mark.
DO NOT ALLOW more than one tick in a row.

Real size = image size ÷ magnification = 45 mm ÷ 300 = 0.15 mm. Convert: 0.15 mm × 1000 = 150 µm.

First check the answer on the answer line. If answer = 150 (µm) award 2 marks.
Rearranges/substitutes: 45 ÷ 300 (= 0.15 mm) (1 mark, method)
Converts to µm: 150 (1 mark, accuracy)
ALLOW 1 mark for 0.15 with no conversion. ECF for a correct conversion of an incorrect value. AO2.1

Fewer sticklebacks means fewer snails are eaten, so snail numbers rise. Herons lose a food source so their numbers fall. More snails then eat more algae, so algae fall.

Any two from:
number of water snails increases / less predation on snails (1)
number of herons decreases / less food for herons (1)
number of algae decreases because more snails eat them (1)
IGNORE 'die' without reference to numbers. DO NOT ALLOW snails decrease. AO2.1

Moving ions from low to high concentration is active transport. It goes against the concentration gradient, so it requires energy released by respiration.

active transport (1)
moves ions against the concentration gradient / from low to high concentration, which needs energy (from respiration) (1)
DO NOT ALLOW diffusion or osmosis. AO1.1, AO2.1

A correlation does not show cause. Other variables may differ between the groups and could explain the result.

shows a correlation / link only, not a cause (1)
other factors / confounding variables (e.g. smoking, exercise, family history) not controlled / may be responsible / no mechanism shown (1)
IGNORE 'sample too small' as 5000 is large. AO3.2b

Gametes combine from two parents, giving varied offspring. If conditions change, some individuals will be adapted and survive to reproduce.

produces genetic variation in offspring / offspring not identical (1)
so some may survive environmental change / disease and reproduce, passing on alleles (1)
ALLOW ORA for asexual reproduction. AO1.1, AO2.1

Contrast cause (pathogen or not) and transmission (spreads or not).

Any two from:
communicable are caused by pathogens / non-communicable are not (1)
communicable can be passed from person to person / non-communicable cannot (1)
non-communicable often linked to lifestyle / genes / environment (1)
IGNORE 'one is curable'. AO1.1

A reflex arc passes through sensory, relay and motor neurons to the effector without conscious thought.

sensory neuron carries impulse to the spinal cord / CNS and relay neuron (1)
motor neuron carries impulse to effector / muscle (1)
ALLOW 1 mark for correct order of receptor, sensory, relay, motor, effector if neurons are not described. AO1.1

The independent variable is the one deliberately changed. Others that affect photosynthesis rate must be kept constant.

distance of lamp from the pondweed / light intensity (1)
any one control: temperature (e.g. water bath), carbon dioxide concentration, size/same piece of pondweed, time counted (1)
DO NOT ALLOW number of bubbles (dependent variable). AO3.3a

30 ÷ 200 × 100 = 15%. Mitosis copies the chromosomes and shares them equally, so daughter cells have identical DNA.

15 (%) (1)
DNA / chromosomes copied exactly (then shared equally) (1)
AO2.1, AO1.1

The value 21 is far from the others. Excluding it, total = 4+6+5+7+5+6+4+5+7 = 49. Mean = 49 ÷ 9 = 5.4 (to 1 d.p.).

Total 1.8 marks (0.6 each). 21 identified as anomaly (AO3.2b) [0.6]. Reasonable reason, e.g. quadrat placed on a dense patch / counting error / not random placement (AO2.1) [0.6]. Mean = 49 ÷ 9 = 5.4 [0.6]. ALLOW 5.44 or 5.4. ECF if wrong anomaly excluded. IGNORE 'human error' with no detail.

With fewer minnows, fewer water fleas are eaten so their numbers rise. More water fleas eat more algae, so the algae population falls.

Total 1.8 marks (0.9 each). Water fleas increase because fewer eaten by / less predation by minnows (AO2.1) [0.9]. Algae decrease because more water fleas feeding on them (AO2.1) [0.9]. Direction and reason both needed for each mark. IGNORE effects on the heron.

Soil nitrate concentration is lower than in the root cell, so uptake is by active transport using energy. Nitrate supplies nitrogen to make amino acids and proteins needed for growth.

Total 1.8 marks (0.9 each). Active transport / against the concentration gradient (AO1.1) [0.9]. To make amino acids / proteins (AW) for growth (AO1.2) [0.9]. DO NOT ALLOW diffusion or osmosis. DO NOT ALLOW 'to make glucose'.

The study shows a correlation only. Other risk factors may differ between the groups. Matching groups for these factors, using larger samples or identifying how the meat could damage cells would strengthen the evidence.

Total 1.8 marks. Correlation does not mean causation / only shows a link (AO3.1a) [0.6]. Other factors may differ between groups, e.g. smoking, exercise, fibre (AO3.2b) [0.6]. One valid improvement: control/match other variables, larger sample, repeat studies, investigate mechanism (AO3.3a) [0.6]. IGNORE 'more tests' with no detail.

Clones keep the high-yield, good-tasting features of the parent. But with no variation, no plants are likely to be resistant to a new disease or change in conditions, so the whole crop is at risk.

Total 1.8 marks (0.9 each). Advantage: offspring have the same desirable characteristics as parent/ uniform crop (AO2.1) [0.9]. Disadvantage: no genetic variation so all equally susceptible to a new disease/change in environment (AO2.1) [0.9]. Reason must be given with each.

Communicable means a pathogen can be passed between individuals, here via water. Treating or boiling drinking water kills the bacteria and breaks the transmission route.

Total 1.8 marks. Caused by a pathogen / bacterium (AO1.1) [0.6]. Can be passed on / spread between people (AO1.1) [0.6]. One valid control, e.g. boil/chlorinate water, safe sewage disposal, handwashing (AO2.1) [0.6]. IGNORE vaccination unless a cholera vaccine is stated.

Magnification = 48 ÷ 0.06 = 800.

First check the answer on the answer line. If answer = 800 (or ×800) award 1.8 marks. If incorrect: correct substitution 48 ÷ 0.06 [0.9]; ALLOW 48 000 ÷ 60 (unit conversion). ECF for arithmetic slip [0.9 max for method]. DO NOT ALLOW a unit such as mm with the answer. (AO2.2)

This is a reflex action. The impulse passes via a relay neuron in the spinal cord without involving conscious thought, so it is rapid and limits tissue damage.

Total 1.8 marks. Reflex (action) (AO1.1) [0.6]. Fast / rapid / does not involve the conscious part of the brain (AO1.2) [0.6]. Protects against / reduces damage or injury (AO2.1) [0.6]. DO NOT ALLOW 'voluntary'.

The student changes temperature (independent) and measures the time for starch to disappear (dependent). Anything else that could alter the rate, such as enzyme concentration, starch volume or pH, must be kept the same.

Total 1.8 marks (0.6 each). Independent variable = temperature (AO2.2) [0.6]. Dependent variable = time taken for starch to disappear / rate of reaction (AO2.2) [0.6]. One control variable: volume or concentration of amylase/starch, pH, volume of solution (AO3.3a) [0.6]. DO NOT ALLOW 'amount' alone without stating what.

(a) Nitrate provides nitrogen, which plants need to make amino acids and so proteins (including chlorophyll-related proteins and enzymes). (b) Soil water usually has a lower nitrate concentration than the root hair cell. Diffusion only moves particles down a concentration gradient, so active transport using energy from respiration is needed to move them in.

(a) 1 mark (AO1.1): amino acids / proteins ✓. ALLOW (making) protein / enzymes / DNA / nitrogen-containing compounds. DO NOT ALLOW 'to make food' or 'glucose' or 'starch'.
(b) 1 mark (AO2.1): moving against the concentration gradient / from low to high concentration ✓ (and requires energy from respiration). ALLOW AW: concentration in soil is lower than in the root hair cell. IGNORE 'faster'.

(a) The dependent variable is the one measured: the volume of oxygen gas produced in 60 seconds. (b) Any other factor affecting enzyme activity must be kept the same, for example the concentration or volume of hydrogen peroxide, the mass of catalase source or the pH, so that any change in rate is caused only by temperature.

(a) 1 mark (AO2.2): volume of oxygen (gas) (collected/produced) ✓. ALLOW rate of oxygen production. DO NOT ALLOW temperature or time.
(b) 1 mark (AO3.3a): a valid control variable AND a reason, e.g. concentration/volume of hydrogen peroxide / mass or amount of catalase / pH / time ✓ so that only temperature affects the rate / so it is a fair test / valid results. Both the variable and the reason are needed for the mark. DO NOT ALLOW temperature.

magnification = image size ÷ real size = \(36 \div 0.012 = 3000\).

First check the answer on the answer line. If answer = 3000 award 1.75 marks.
Substitution into the equation: 36 ÷ 0.012 (1 mark, method)
Answer 3000 (0.75 mark, accuracy)
ALLOW ×3000 / 3 × 10^3. ALLOW 36000 ÷ 12 as method. DO NOT ALLOW 0.00033 (equation inverted) for the answer mark; ECF the method mark only. AO2.1 / AO3.1a.

Mean per quadrat = \((4+7+5+8+6) \div 5 = 6\). Mean per m² = \(6 \div 0.25 = 24\). Total = \(24 \times 600 = 14\,400\).

First check the answer on the answer line. If answer = 14 400 award 1.75 marks.
Mean per quadrat = 6 (0.5 mark)
Density per m² = 6 ÷ 0.25 = 24 (0.5 mark)
24 × 600 = 14 400 (0.75 mark)
ALLOW alternative route: 600 ÷ 0.25 = 2400 quadrats × 6 = 14 400. ECF from an incorrect mean. DO NOT ALLOW 3600 (area not accounted for) for the answer mark. AO2.1 / AO2.2.

Change in mass = \(2.82 - 2.40 = 0.42\) g. \((0.42 \div 2.40) \times 100 = 17.5\%\) increase.

First check the answer on the answer line. If answer = 17.5 (%) award 1.75 marks.
Change in mass = 0.42 (g) (0.75 mark)
(0.42 ÷ 2.40) × 100 (0.5 mark)
17.5 (0.5 mark)
ALLOW +17.5 / 17.50. DO NOT ALLOW 18 (not 1 decimal place) for the answer mark. DO NOT ALLOW 14.9 (divided by final mass). AO2.1.

rate = volume ÷ time = \(13.5 \div 9 = 1.5\) cm³ per minute.

First check the answer on the answer line. If answer = 1.5 award 1.75 marks.
13.5 ÷ 9 (1 mark, method)
1.5 (0.75 mark, accuracy)
ALLOW 1.50. DO NOT ALLOW 0.67 / 0.7 (inverted) for the answer mark; ECF the method mark only. AO2.1.

Root hair cells have long thin extensions, giving a large surface area for absorption. Water moves into them by osmosis from the soil (higher water potential) to the cell (lower water potential). Nitrate ions are usually at a lower concentration in the soil than in the root cell, so they are taken in by active transport, which needs energy released by aerobic respiration. Nitrate ions are used to make amino acids and proteins (and chlorophyll), so a shortage reduces growth and causes yellow leaves. In waterlogged soil the air spaces are filled with water so less oxygen is available. The root cells cannot respire aerobically, release less energy, and so less active transport of nitrate ions takes place. Roots also grow poorly, which reduces the surface area for uptake further.

Level 3 (5-6 marks): Gives a clear, detailed explanation covering both bullet points, linking at least four correct points from the indicative content, including active transport needing energy from respiration and the effect of both nitrate shortage and waterlogging. Scientific terms used accurately; the answer is well structured and logical. (6 marks = all aspects fully linked and clear; 5 marks = minor omissions or lack of clarity.)

Level 2 (3-4 marks): Gives a partial explanation covering both bullet points with some correct links, or a detailed explanation of one bullet point only. Some scientific terms used correctly. (4 marks = both aspects addressed but with gaps; 3 marks = mostly one aspect or limited linking.)

Level 1 (1-2 marks): Gives simple statements, such as roots take in water and minerals, or nitrates are needed for growth, with little or no explanation. Limited use of scientific terms; the answer may lack structure.

Level 0 (0 marks): No response or no response worthy of credit.

Indicative content (AO1.1, AO1.2, AO2.1):
- root hair cells have a large surface area (AO1.1)
- water enters by osmosis (AO1.1)
- down a water potential gradient / from high to low water potential (AO1.1)
- nitrate ions are taken in by active transport (AO1.1)
- against a concentration gradient (AO1.2)
- active transport requires energy from (aerobic) respiration (AO1.2)
- nitrate ions are used to make amino acids / proteins / chlorophyll (AO1.1)
- a nitrate shortage means less protein synthesis, so less growth / yellow leaves (AO2.1)
- waterlogged soil has little oxygen / air spaces filled with water (AO2.1)
- so less aerobic respiration, less energy, less active transport of ions, poor root growth (AO2.1)

Guidance: ALLOW 'minerals' for nitrate ions if linked to uptake. ALLOW 'diffusion' for water entry only if osmosis is not contradicted (AW). DO NOT ALLOW 'plants respire only in the dark' or 'roots make food by photosynthesis'. IGNORE comments about fertiliser cost. The communication of ideas decides the mark within a level.

Less than 60 minutes: \( \frac{150}{1000} \times 100 = 15\% \). 60 to 150 minutes: \( \frac{135}{1500} \times 100 = 9\% \). More than 150 minutes: \( \frac{90}{1500} \times 100 = 6\% \). The percentage developing CVD falls as walking time increases, so there is a negative correlation. A correlation does not prove that walking causes the lower risk. Other factors could differ between the groups, such as diet, smoking, alcohol, body mass, inherited (genetic) risk, age, and environmental factors like air pollution or access to safe places to walk. People who are already unwell may walk less, so the cause may be reversed. The headline is therefore too strong; the data are consistent with walking reducing risk, but a controlled study would be needed.

Level 3 (5-6 marks): Gives a clear evaluation that uses calculated percentages from at least two groups to describe the trend AND explains clearly that correlation does not prove causation, with at least two specific other factors (lifestyle, genetic or environmental). Reaches a justified judgement about the headline. Well structured, accurate scientific terms. (6 marks = fully developed with judgement; 5 marks = minor gaps.)

Level 2 (3-4 marks): Describes the trend using the data (with some calculation) and makes some attempt to question the headline, or gives a detailed discussion of other factors without using the data. Some correct scientific terms.

Level 1 (1-2 marks): Makes simple statements such as 'more walking means fewer people with CVD' or 'other things could cause it' with little use of data or explanation.

Level 0 (0 marks): No response or no response worthy of credit.

Indicative content (AO2.1, AO3.1a, AO3.2b):
- less than 60 min: 150/1000 = 15% (AO2.1)
- 60 to 150 min: 135/1500 = 9% (AO2.1)
- more than 150 min: 90/1500 = 6% (AO2.1)
- as walking increases, percentage with CVD decreases / negative correlation (AO3.1a)
- correlation does not show cause (AO3.2b)
- other risk factors may differ between groups: diet, smoking, body mass, alcohol, stress (AO3.2b)
- genes / family history may affect CVD risk (AO1.1)
- environment, e.g. air pollution or income / access to healthcare (AO1.1)
- healthier people may be able to walk more (reverse causation) (AO3.2b)
- a trial with matched or randomly allocated groups would be needed / walking time self-reported so may be inaccurate (AO3.3a)

Guidance: ALLOW percentages to the nearest whole number. ECF for a wrongly calculated percentage if the trend described is consistent with it. ALLOW 'the headline is partly supported'. DO NOT ALLOW 'walking definitely causes' without evaluation. IGNORE sample size comments unless they are justified (4000 is a large sample). The communication of ideas decides the mark within a level.