Mark Scheme

Section A: 1. B; 2. B; 3. C; 4. B; 5. B; 6. B. (6)

7 (a) equal-sized cylinders (1); blotted and massed before/after (1); controlled time/temperature/volume (1). (b) water concentration higher outside than inside (1); water enters by osmosis (1); across the partially permeable membrane (1). (c) allows for different starting masses (1); so a fair comparison (1). (8)

8 (a) any two: skin barrier; mucus and cilia in airways; stomach acid (2). (b) phagocytosis (1); produce antibodies (1); produce antitoxins (1). (c) overuse selects for resistant bacteria (1); resistant ones survive and reproduce (1); passing on resistance (1). (8)

9 (a) pancreas (1). (b) pancreas releases insulin (1); cells take up glucose (1); excess stored as glycogen (1). (c) Type 1: no insulin produced, treated with injections (2); Type 2: cells stop responding to insulin, linked to obesity, treated with diet/exercise (2). (8)

10 (a) dominant: shown with one copy (1); recessive: needs two copies (1). (b) Ff × Ff → FF, Ff, Ff, ff (1); ff has cystic fibrosis (1); probability 1 in 4 / 25% (1). (c) sex chromosomes XX female, XY male (1); 50% chance from the sperm carrying X or Y (1). (8)

11 (a) vary distance of a lamp (1); measure bubbles of O₂ per minute / gas volume (1); use 1/distance² for light intensity (1). (b) another factor (CO₂ or temperature) becomes limiting (1); so increasing light no longer increases the rate (1). (5)

12 (a) place quadrats randomly (1); count plants / find mean per quadrat (1); scale up by total area (1). (b) abiotic example with effect (e.g. less light → fewer plants) (2); biotic example with effect (e.g. new predator → prey fall) (2). (7)

13 (a) algae and plants evolved (1); photosynthesis produced oxygen (1). (b) any two: ice melting/sea level rise; extreme weather; changing species distribution; reduced food production (2). (4)

14 (a) glucose + oxygen → carbon dioxide + water (1). (b) aerobic uses oxygen, anaerobic does not (1); aerobic releases much more energy per glucose (1); anaerobic produces lactic acid (incomplete breakdown) (1). (c) add iodine solution (1); turns blue-black if starch is present (1). (d) they speed up reactions (without being used up) by lowering the activation energy (1). (7)

15 (a) diffusion is the net movement of particles from high to low concentration and needs no energy (1); active transport moves particles against the gradient (low → high) and requires energy from respiration (1). (b) meiosis (1); a gamete has half the number of chromosomes of a body cell (1). (c) any one with reason: very large surface area (villi/microvilli) (1); thin walls / good blood supply for a steep concentration gradient (1). (6)

16 — Levels (6): Indicative: vaccine contains dead/inactive pathogen or antigens; white blood cells produce antibodies; memory cells remain; on re-infection, faster and larger response destroys the pathogen before illness. Herd immunity: if most people are immune, the pathogen cannot spread easily, protecting the unvaccinated.

• L3 (5–6): Explains the memory-cell mechanism and herd immunity clearly.
• L2 (3–4): Some of the mechanism or herd immunity.
• L1 (1–2): Simple statements.

17 — Levels (6): Indicative: there is variation in a bacterial population; antibiotics kill the non-resistant bacteria; random mutation makes some bacteria resistant; these survive and reproduce, passing on the resistance allele; over generations the resistant strain becomes common (natural selection). Overuse and not completing courses speed this up.

• L3 (5–6): Full selection sequence (variation → survival → reproduction → spread) linked to antibiotic overuse.
• L2 (3–4): Several correct steps.
• L1 (1–2): Simple statements.

18 — Levels (6): Indicative: photosynthesis removes CO₂ from the air, fixing carbon into glucose/plant material; carbon passes along food chains by feeding; respiration in plants, animals and decomposers returns CO₂; combustion of wood and fossil fuels returns CO₂; decomposers (microorganisms) break down dead organisms and waste, releasing CO₂.

• L3 (5–6): Correctly named processes for both removal and return of carbon, linked into a cycle.
• L2 (3–4): Several processes with some links.
• L1 (1–2): Isolated statements.

19 — Levels (6): Indicative: the rate of photosynthesis is limited by light intensity, carbon dioxide concentration and temperature. The grower can increase light (lamps), increase CO₂ (burners/cylinders) and keep the temperature warm (heaters) so that no single factor limits the rate; faster photosynthesis means more glucose for growth and a higher yield. Temperature must not be so high that enzymes denature. There is a cost/benefit balance.

• L3 (5–6): Explains the three limiting factors and links increasing them to higher rate/yield.
• L2 (3–4): Some factors linked to rate.
• L1 (1–2): Simple statements.

20 — Levels (6): Indicative: human activities reduce biodiversity through deforestation (habitat loss), pollution (air, water, land), and land use for building/farming/quarrying; rising population and waste increase the impact. Ways to maintain biodiversity (any two): breeding programmes/protected species; protection and regeneration of habitats; reducing deforestation; recycling resources rather than landfill; reintroducing hedgerows/field margins.

• L3 (5–6): Explains causes of biodiversity loss and two valid maintenance measures.
• L2 (3–4): Some causes and/or one measure.
• L1 (1–2): Simple statements.

21 — Levels (4): Indicative: stimulus → receptor → sensory neurone → relay neurone in the CNS → motor neurone → effector → response; impulses cross synapses by chemical transmitters; the response is automatic and does not involve conscious thought, making it rapid and protective.

• L2 (3–4): Correct ordered pathway with most structures named.
• L1 (1–2): Some structures named.

Sample Answers with Examiner Commentary

Question 16 — Sample Answers

Grade 9 answer "A vaccine contains a dead or inactivated form of the pathogen, or its antigens. When injected, the white blood cells recognise the antigens and produce specific antibodies, and importantly they also produce memory cells that stay in the blood. If the real pathogen later enters the body, these memory cells allow antibodies to be produced much faster and in greater numbers, destroying the pathogen before the person becomes ill — this gives long-term protection. If a large proportion of the population is vaccinated, the pathogen cannot spread easily from person to person, so even people who are not vaccinated are protected. This is called herd immunity." Mark: 6/6. Examiner commentary: Both required ideas — the memory-cell basis of long-term immunity and herd immunity — are explained accurately. Top band.

Grade 6 answer "A vaccine has a weak version of the pathogen so your white blood cells make antibodies. Next time you can fight it off quickly. If lots of people are vaccinated the disease can't spread as easily." Mark: 4/6. Examiner commentary: Correct on antibody production, the faster secondary response and herd immunity, but it does not mention memory cells, the key to long-term protection. That omission caps it below the top band.

Question 9(c) — Sample Answers

Grade 9 answer "In Type 1 diabetes the pancreas produces little or no insulin, so it is treated with insulin injections. In Type 2 diabetes the body cells stop responding to insulin; it is strongly linked to obesity and is usually treated with a controlled diet and regular exercise." Mark: 4/4. Examiner commentary: Cause and treatment correct for both types, with the obesity risk factor for Type 2. Full marks.

Grade 6 answer "Type 1 is when you don't make insulin and need injections. Type 2 is when your body doesn't use insulin properly and you control it with diet." Mark: 3/4. Examiner commentary: Correct causes and treatments, but the link between Type 2 and obesity is missing, which is a commonly credited marking point.