Mark Scheme

Section A: 1. D; 2. C (0.05 mm × 1000 = 50 µm); 3. C; 4. D; 5. B. (5 marks)

6 (a) Osmosis is the diffusion / movement of water (1) across a partially permeable membrane from a dilute solution (high water concentration) to a concentrated solution (low water concentration) (1). (2) 6 (b) The cylinders had different starting masses (1); percentage change allows a fair comparison between them (1). (2) 6 (c) The sugar solution was more concentrated (lower water concentration) than the cell contents (1); so water moved out of the cells by osmosis (1); down the water concentration gradient / across the partially permeable membrane (1). (3) 6 (d) Any two: temperature; time left in solution; size/surface area of cylinders; volume of solution; same type of potato. (2)

7 (a) Blood passes through the heart twice for each circuit of the body (1); one loop goes to the lungs, the other to the rest of the body (1). (2) 7 (b) The left ventricle pumps blood all around the body (1), so needs to generate a higher pressure / contract more forcefully (1). (2) 7 (c) Any two: thick / muscular / elastic walls (1); to withstand high pressure / stretch and recoil (1); narrow lumen. (2) 7 (d) Statins: drug that lowers blood cholesterol / slows fatty build-up (1); but must be taken long-term / possible side effects (1). Stents: hold the artery open / keep blood flowing (1); but risk of infection or clots during surgery (1). (4)

8 (a) Protease (1); amino acids (1). (2) 8 (b) At extreme pH the active site changes shape (1); so the substrate no longer fits (1); fewer enzyme-substrate complexes form / reaction slows (1). (3) 8 (c) Mix amylase, starch and a buffer (1); at set times remove a sample and add to iodine (1); record the time when the iodine stays orange/brown (no longer turns blue-black) (1). (3)

9 (a) Phagocytosis / engulf and digest pathogens (1); produce antibodies (1); produce antitoxins (1). (3) 9 (b) Vaccine contains dead / inactive pathogen or antigens (1); white blood cells produce antibodies (1); memory cells remain (1); on re-infection the response is faster and larger, destroying the pathogen before illness (1). (4) 9 (c) Antibiotics kill bacteria (1); viruses reproduce inside cells, so are hard to target without damaging body cells (1). (2)

10 (a) carbon dioxide + water → glucose + oxygen (1 for reactants, 1 for products). (2) 10 (b) Any two factors with explanation: increase light intensity → more energy for the reaction (1+1); increase CO₂ concentration → more reactant available (1+1); increase temperature (to optimum) → particles have more energy / more collisions (1+1). (4)

11 — Levels of response (6 marks): Indicative content: Aerobic uses oxygen; reactant glucose; products carbon dioxide and water; releases a lot of energy; occurs in mitochondria; happens most of the time / during gentle exercise. Anaerobic occurs without oxygen; in muscles produces lactic acid; releases much less energy; happens during vigorous exercise when oxygen cannot be supplied fast enough; leads to oxygen debt.

• Level 3 (5–6 marks): A detailed comparison covering reactants, products, energy and conditions for both types, clearly linked.
• Level 2 (3–4 marks): Describes both types with some comparison; may miss energy difference or conditions.
• Level 1 (1–2 marks): Simple statements about one or both types with little comparison.
• 0 marks: No relevant content.

Sample Answers with Examiner Commentary

Question 11 — Sample Answers

Grade 9 (top of Higher) answer "Both aerobic and anaerobic respiration release energy from glucose for the cells to use, and both are exothermic. In aerobic respiration, glucose reacts with oxygen to produce carbon dioxide and water, and it releases a large amount of energy. It happens in the mitochondria and occurs most of the time, including during gentle exercise. In anaerobic respiration there is not enough oxygen, so glucose is only partly broken down. In human muscle cells this produces lactic acid and releases much less energy. It happens during vigorous exercise when the heart and lungs cannot supply oxygen fast enough, and it creates an oxygen debt that must be repaid afterwards." Mark: 6/6. Examiner commentary: A complete comparison — reactants, products, relative energy and conditions are all covered for both types, with accurate terminology (mitochondria, lactic acid, oxygen debt). This is clearly top-band.

Grade 6 (solid pass) answer "Aerobic respiration uses oxygen and makes carbon dioxide and water. It releases lots of energy. Anaerobic respiration does not use oxygen and makes lactic acid in the muscles. It releases less energy and happens when you exercise hard." Mark: 4/6. Examiner commentary: A solid response that correctly states the reactants/products and the energy difference, and identifies lactic acid and vigorous exercise. It does not mention glucose as the reactant for both, or where aerobic respiration occurs, which would have pushed it into the top band.

Grade 3 (near miss) answer "Respiration is breathing in and out. Aerobic uses air and anaerobic doesn't. Anaerobic makes acid which makes your muscles hurt." Mark: 2/6. Examiner commentary: Contains the common misconception that respiration is "breathing" — respiration is a chemical reaction in cells, not gas exchange in the lungs. There is a small amount of credit for "no oxygen in anaerobic" and "makes acid", but the answer lacks the reactants, products and energy comparison needed to progress.

Question 9(b) — Sample Answers

Grade 9 answer "The vaccine contains a small amount of dead or inactivated pathogen, which still carries the antigens. The white blood cells (lymphocytes) recognise these antigens and produce specific antibodies. Memory cells are also made and remain in the blood. If the live pathogen later infects the person, the memory cells allow antibodies to be produced much more quickly and in greater numbers, destroying the pathogen before the person becomes ill." Mark: 4/4. Examiner commentary: All four marking points are present and in a logical order, with correct use of "antigen", "antibody" and "memory cells".

Grade 6 answer "The vaccine has a weak version of the pathogen in it. Your white blood cells make antibodies against it. Then if you catch the real disease your body can fight it off quickly." Mark: 3/4. Examiner commentary: Credit for dead/inactive pathogen, antibody production, and the faster secondary response. The omission of memory cells is the one missing marking point that separates this from full marks.