Mark Scheme

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

7 (a) nervous: fast, short-lived (1); hormonal: slower, longer-lasting (1). (b) pituitary (1); in the brain (1). (c) pancreas releases glucagon (1); glycogen converted to glucose (1); released into the blood (1). (8)

8 (a) ciliary muscles contract (1); suspensory ligaments slacken (1); lens becomes thicker/more curved (1). (b) image forms in front of the retina (1); corrected with a concave/diverging lens (1). (5)

9 (a) blood filtered under pressure (1); useful substances reabsorbed — all glucose, some ions and water (1); urea/excess water/ions form urine (1). (b) more ADH → more water reabsorbed (1); small volume (1); concentrated urine (1). (c) dialysis: regular, restrictive, risk of infection (2); transplant: near-normal life but donor shortage / rejection risk needing immunosuppressants (2). (10)

10 (a) transcription: gene copied into mRNA (1) which leaves the nucleus (1); translation: mRNA attaches to ribosome (1); amino acids joined in order to form the protein (1). (b) changes the base sequence (1); may change the amino acid sequence / shape of the protein (1). (c) Tt × tt → Tt, Tt, tt, tt (1 square); 2 tall : 2 short (1) = 1:1 (1). (9)

11 (a) Kingdom, Phylum, Class, Order, Family, Genus, Species (2). (b) three domains: Archaea, Bacteria, Eukaryota (1); based on DNA/RNA evidence (1); replaced earlier systems as technology improved (1). (c) choose parents with the desired characteristic (1); breed them and select offspring with the characteristic over generations (1); risk: reduced variation / inbreeding (1). (8)

12 (a) a stage/level in a food chain (1). (b) not all is eaten/digested (lost in faeces) (1); energy used in respiration/movement (1); lost as heat (1). (c) any two: restrict animal movement/keep warm; high-protein feed; fishing quotas; net size; mycoprotein (2). (6)

13 (a) warmth; moisture; oxygen (3). (b) decomposers break down dead organisms (1); respiration releases CO₂ back to the atmosphere (1). (5)

14 (a) both produced in the pituitary gland (1); FSH causes an egg/follicle to mature in the ovary (1); LH triggers ovulation/release of the egg (1). (b) contains oestrogen and/or progesterone (1); which inhibits FSH so no eggs mature (1). (c) FSH and LH given to stimulate eggs to mature and be released (1); eggs collected and fertilised by sperm in the lab (1); one or two embryos developed and inserted into the uterus (1). (d) advantage: helps a couple who cannot conceive to have a baby (1); disadvantage: low success rate / physically and emotionally stressful / risk of multiple births (1). (10)

15 — Levels (6): Indicative: monitored by the thermoregulatory centre (hypothalamus). Too hot: vasodilation (more blood to skin surface → more heat lost); sweating (evaporation transfers energy). Too cold: vasoconstriction (less blood to surface → less heat lost); shivering (respiration releases heat); sweating stops; hairs raised. Negative feedback restores 37 °C.

• L3 (5–6): Both hot and cold responses, with correct mechanisms (vasodilation/vasoconstriction, sweating, shivering).
• L2 (3–4): Some correct responses for both or detailed for one.
• L1 (1–2): Simple statements.

16 — Levels (6): Indicative: antibiotics kill non-resistant bacteria; random mutation makes some bacteria resistant; these survive and reproduce, passing on the resistance allele; over time the resistant strain dominates (natural selection). Overuse/incomplete courses speed this up. To reduce spread: doctors should not over-prescribe antibiotics; patients should complete the full course; restrict use in agriculture; good hygiene to limit transmission.

• L3 (5–6): Explains the selection mechanism and gives ways to reduce spread.
• L2 (3–4): Some of the mechanism or some control measures.
• L1 (1–2): Simple statements.

17 — Levels (6): Indicative: auxin is a plant hormone made at the shoot tip; it is unequally distributed, accumulating on the shaded side; auxin promotes cell elongation, so the shaded side grows faster/longer; this makes the shoot bend towards the light (positive phototropism). Commercial uses (any two): as weedkillers (selective herbicides); as rooting powders to promote root growth in cuttings; to control ripening of fruit; to produce seedless fruit / control dormancy.

• L3 (5–6): Correct auxin explanation of bending and two valid uses.
• L2 (3–4): Some of the mechanism and/or one use.
• L1 (1–2): Simple statements.

18 — Levels (6): Indicative: blood glucose is monitored by the pancreas. When it rises (after a meal): the pancreas releases insulin; insulin makes liver and muscle cells take up glucose; excess glucose is stored as glycogen, lowering blood glucose. When it falls: the pancreas releases glucagon; glycogen in the liver is converted back to glucose and released into the blood, raising it. These opposing responses are negative feedback that restores the normal level.

• L3 (5–6): Both rise and fall explained with correct hormones (insulin/glucagon), organs and glycogen.
• L2 (3–4): One direction fully or both partially.
• L1 (1–2): Simple statements.

19 — Levels (6): Indicative: there is genetic variation within a species; if a population becomes isolated, different environments/selection pressures favour different alleles; the best-adapted individuals survive and reproduce, passing on beneficial alleles; over many generations the populations become so different they can no longer interbreed to produce fertile offspring — a new species. Fossils show how organisms have changed over millions of years and provide a record of extinct forms.

• L3 (5–6): Speciation by natural selection and the fossil evidence explained.
• L2 (3–4): Some of the process or the evidence.
• L1 (1–2): Simple statements.

20 — Levels (4): Indicative: deforestation removes habitats and food, so the number and variety of species (biodiversity) falls. It also reduces photosynthesis, so less CO₂ is removed from the air, while burning and the decay of felled trees release CO₂, increasing the atmospheric concentration.

• L2 (3–4): Links deforestation to both reduced biodiversity and increased CO₂ with reasons.
• L1 (1–2): Simple statements about one effect.

Sample Answers with Examiner Commentary

Question 15 — Sample Answers

Grade 9 answer "Body temperature is monitored by the thermoregulatory centre in the brain (the hypothalamus), which contains receptors sensitive to blood temperature. When the body is too hot, the blood vessels supplying the skin capillaries widen (vasodilation), so more blood flows near the surface and more heat is lost to the surroundings, and the sweat glands release sweat which evaporates, transferring energy away from the skin. When the body is too cold, the skin blood vessels narrow (vasoconstriction) so less heat is lost, sweating stops, and the muscles contract rapidly (shivering), and this respiration releases heat. These responses are an example of negative feedback that keeps the core temperature around 37 °C." Mark: 6/6. Examiner commentary: Both hot and cold responses are covered with the correct mechanisms (vasodilation/vasoconstriction, sweating, shivering) and the controlling centre, framed as negative feedback. Top band.

Grade 6 answer "When you are hot you sweat and the blood vessels widen so you lose heat. When you are cold you shiver and the blood vessels get narrower so you keep heat in." Mark: 4/6. Examiner commentary: Correct responses for both hot and cold, but the technical terms vasodilation/vasoconstriction are not used and the controlling centre is not named — adding these would secure the top band.

Question 9(b) — Sample Answers

Grade 9 answer "If the blood is too concentrated, more ADH is released from the pituitary gland. This makes the kidney tubules more permeable so more water is reabsorbed back into the blood, producing a small volume of concentrated urine." Mark: 3/3. Examiner commentary: Correctly links more ADH to increased water reabsorption and to a small volume of concentrated urine.

Grade 6 answer "More ADH means more water is kept in the body so you make less urine." Mark: 2/3. Examiner commentary: Credit for more water reabsorbed and a smaller volume, but it does not say the urine is more concentrated, the third marking point.