OxfordAQA International GCSE Biology: Infection, immunity, vaccination and antibiotics (9201) – Practice Questions

These are original questions written for Marlbridge, for revision and practice on this content. They are not reproduced past-paper questions, and they do not replicate the exam’s exact structure, question count or mark tariffs – examination boards hold copyright in their own papers. Use these alongside the official past papers from your board or school.

These questions cover section 3.4.7 (Infection and response, parts a to j) of the OxfordAQA International GCSE Biology (9201) specification, Version 5.2, for exams May/June 2018 onwards, including the required practical on disinfectants and antibiotics. The qualification is untiered. Learn the content first from the study guide or the revision notes. The course hub is OxfordAQA IGCSE Biology and the printable list is the checklist.

Questions

1. (a) State what is meant by a pathogen. [1] (b) Name two types of pathogen. [2]

2. Explain how bacteria and how viruses make a person ill. [4]

3. Describe how white blood cells defend the body against pathogens in three different ways. [6]

4. A culture starts with 1000 bacteria. Each bacterium divides once every 20 minutes. Calculate the number of bacteria after 3 hours. [3]

5. A child is given a vaccine containing an inactive form of a virus. Explain why the child does not become ill from the vaccine but is protected if the virus enters the body months later. [4]

6. A town has 600 people. A vaccination programme means that 85% of them are immune to a disease. (a) Calculate how many people are not immune. [2] (b) Explain why the disease spreads less easily than it would if nobody were immune. [2] (c) Explain why a baby too young to be vaccinated is helped by the programme. [1]

7. Evaluate the advantages and disadvantages of a child being vaccinated with the MMR vaccine against measles. [6]

8. A patient has flu, which is caused by a virus, and asks the doctor for antibiotics. (a) Explain why the doctor refuses. [2] (b) Explain why a different bacterial disease must be treated with an antibiotic chosen for it. [1] (c) Suggest why it is difficult to develop a drug that kills viruses. [1]

9. A student tests three disinfectants on a lawn of bacteria on agar. Paper discs soaked in each disinfectant, and a disc soaked in sterile water, are placed on the lawn. After incubation the clear zones have these diameters: disinfectant A 14 mm, disinfectant B 22 mm, disinfectant C 6 mm, water 0 mm. (a) Calculate the area of the clear zone for disinfectant B. Give your answer to 1 decimal place. [2] (b) Calculate how many times larger the clear zone for B is than for A. Give your answer to 2 decimal places. [2] (c) State the conclusion from the three zone sizes. [1] (d) State the purpose of the water disc. [1] (e) Explain why the lid of the dish should not be completely sealed. [1]

10. A hospital tests bacterial samples from patients for resistance to an antibiotic. In year 1, 38 of 200 samples were resistant. In year 3, 24 of 160 samples were resistant. (a) Calculate the percentage of samples that were resistant in each year. [2] (b) Calculate the percentage fall in the proportion of resistant samples from year 1 to year 3. Give your answer to 1 decimal place. [2] (c) The hospital introduced rules limiting antibiotic use over this period. Suggest how these rules could explain the change. [2]

11. A patient has an infection of 3 million bacteria. Three of them carry a mutation that makes them resistant to antibiotic X. The patient takes antibiotic X, which kills all the non-resistant bacteria. The resistant bacteria then divide once every 30 minutes for 4 hours. (a) Calculate the number of resistant bacteria after 4 hours. [3] (b) Explain why antibiotic X no longer cures this infection. [3] (c) Explain why new antibiotics are needed, and why antibiotics are not currently used for a mild throat infection. [2]

12. Plan an investigation to compare how well three antibiotics kill a harmless bacterium on an agar plate. Include how you keep the culture uncontaminated and how you obtain results. [6]

Answers

1. (a) A microorganism that causes infectious disease. [1] (b) Bacteria [1] and viruses [1]. Total [3] Examiner insight: Naming two types is easier to credit when you write the plain words bacteria and viruses; a vague answer such as germs is risky because it is not a type.

2. Bacteria may produce poisons, called toxins [1], which make the person feel ill [1]. Viruses live and reproduce inside cells [1], which damages the cells [1]. Total [4] Examiner insight: Each pathogen needs its own mechanism. Writing that both simply “cause disease” gives the examiner nothing to credit.

3. Phagocytosis: a white blood cell ingests (takes in) pathogens [1] so they are destroyed [1]. Antibodies: white blood cells produce antibodies that are specific to a particular pathogen [1] and destroy that bacterium or virus [1]. Antitoxins: produced by white blood cells [1] to counteract the toxins released by pathogens [1]. Total [6] Examiner insight: Six marks across three defences usually means two statements for each. Name the defence, then say what it acts on.

4. Divisions in 3 hours = 180 ÷ 20 = 9 [1]. Multiplier = 2⁹ = 512 [1]. Number = 1000 × 512 = 512 000 [1]. Total [3] Examiner insight: If you only reach the multiplier, you have shown the method but not the final answer. Always multiply by the starting number.

5. The vaccine contains an inactive form of the virus, so it cannot cause the disease [1]. It stimulates white blood cells to make antibodies [1]. If the real virus enters later, the correct antibody is made rapidly [1], which destroys the virus before it makes the person ill [1]. Total [4] Examiner insight: A common slip is to say the vaccine “contains antibodies”. Say that it stimulates the body to make them.

6. (a) Not immune = 15% of 600 [1] = 90 people [1]. (b) A large proportion of the population is immune [1], so an infected person is less likely to meet someone who can catch it and the spread is very much reduced [1]. (c) Most of the people around the baby are immune, so the pathogen is less likely to reach the baby [1]. Total [5] Examiner insight: In part (b), “fewer people get it” restates the question. Explain why: infected people meet mostly immune people.

7. Advantages (any three): protects the child from measles [1]; prevents the effects of the disease [1]; increases the proportion of immune people so the spread is reduced, which also protects people who cannot be vaccinated [1]. Disadvantages (any two): the child may have a reaction such as soreness or a fever [1]; the vaccine does not work in every child [1]. A judgement that weighs both sides, for example that the benefits outweigh the small risk [1]. Total [6] Examiner insight: Evaluate means a conclusion as well as two lists. Keep the side effects general, because details of specific vaccines are not needed.

8. (a) Antibiotics cannot kill viruses [1]. Viruses live inside body cells, so the antibiotic does not stop them [1]. (b) Specific bacteria should be treated by specific antibiotics, because an antibiotic that works on one may not kill another [1]. (c) Viruses live and reproduce inside body cells, so a drug that kills them is likely to damage the body’s own tissues [1]. Total [4] Examiner insight: Writing that antibiotics “do not work on flu” earns less than saying why: they kill bacteria, and viruses live inside body cells.

9. (a) r = 22 ÷ 2 = 11 mm [1]. Area = π × 11² = 380.1 mm² [1]. (b) Area of A = π × 7² = 153.9 mm² [1]. Ratio = 380.1 ÷ 153.9 = 2.47 times [1]. (c) Disinfectant B was the most effective against this bacterium, and C the least [1]. (d) It is a control: it shows the liquid alone does not kill the bacteria [1]. (e) Air must be able to enter, otherwise anaerobic bacteria, which may be harmful, could grow [1]. Total [7] Examiner insight: Give units with area (mm²). When you compare areas, using the unrounded area for B and A avoids rounding drift.

10. (a) Year 1: 38 ÷ 200 × 100 = 19% [1]. Year 3: 24 ÷ 160 × 100 = 15% [1]. (b) Fall = 19 − 15 = 4 [1]. Percentage fall = 4 ÷ 19 × 100 = 21.1% [1]. (c) Less use of the antibiotic means resistant bacteria have less advantage over non-resistant ones, because fewer non-resistant bacteria are killed [1]. So resistant bacteria reproduce less and the proportion that are resistant falls [1]. Total [6] Examiner insight: A percentage fall is divided by the starting value, not the final one. Dividing 4 by 15 is a common slip.

11. (a) Divisions = 4 × 60 ÷ 30 = 8 [1]. Multiplier = 2⁸ = 256 [1]. Number = 3 × 256 = 768 [1]. (b) The resistant bacteria survived the antibiotic [1] and reproduced [1], so the population is now the resistant strain, which antibiotic X cannot kill [1]. (c) Resistant strains keep appearing, so new antibiotics have to be developed [1]. Not using antibiotics for non-serious infections such as a mild throat infection slows the rate at which resistant strains develop [1]. Total [8] Examiner insight: Extended explanations are easiest to follow in order: mutation, survival, reproduction, a population of resistant bacteria. Jumping to the conclusion loses the link steps.

12. Sterile equipment and aseptic technique so the culture is uncontaminated [1]; bacteria spread evenly on sterile agar to make a lawn [1]; sterile discs of the same size, soaked in equal volumes of each of the three antibiotics [1]; a control disc soaked in sterile water [1]; lid taped loosely, plate upside down, and incubated at a stated temperature such as about 25 °C for the same time [1]; diameter of each clear zone measured and the area calculated, the larger zone showing the more effective antibiotic [1]. Repeating and taking a mean would improve reliability. Total [6] Examiner insight: A plan scores best when it controls variables by name (same bacterium, same disc size, same time and temperature) and says what is measured.

Where marks are usually lost

• Saying antibiotics treat viral disease, or giving no reason why they do not.
• Writing that bacteria or people “build up resistance” instead of describing mutation, survival and reproduction.
• Mixing up antibodies (act on the pathogen) and antitoxins (counteract the toxin).
• Describing a vaccine as containing living pathogens rather than dead or inactive forms.
• Giving only one side of a vaccination evaluation, or no final judgement.
• Dividing by the wrong value in percentage change, or forgetting that 2 to the power of the number of divisions is the multiplier.
• Comparing clear zones by diameter when the question asks for area, or leaving out mm².
• Planning the practical without a control disc, a stated temperature or a repeat.

Next steps

• Re-read the revision notes and the study guide.
• Go to the OxfordAQA IGCSE Biology hub and tick off topics on the checklist.
• Try all the free 10-minute diagnostics.
• Book a free trial class.

Official syllabus

OxfordAQA International GCSE Biology (9201), section 3.4.7 Infection and response and the required practical on disinfectants and antibiotics. Specification Version 5.2, for exams May/June 2018 onwards, published by OxfordAQA.