This set covers five skills: separating pathogen, transmission and symptoms, explaining barrier defences, modelling the immune response, describing vaccination data, and explaining resistance as selection. Work through the questions in order, since they go from easier to harder.
Write a full answer for each one before you open the working. All data are invented for practice, and this is science revision only. Keep a note of each mistake in the mistake log and retest queue.
Questions
Q1. State what is meant by a pathogen.
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A pathogen is an organism that causes disease. Examples are bacteria, viruses and parasites.
Q2. Dengue is caused by a virus and is spread by mosquito bites. Identify the pathogen and the vector.
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The pathogen is the virus. The vector is the mosquito, which carries the virus from one person to another but is not the cause of the disease.
Q3. Sort into route of transmission or symptom: (a) coughing droplets breathed in, (b) fever, (c) drinking contaminated water, (d) a rash.
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(a) Route of transmission. (b) Symptom. (c) Route of transmission. (d) Symptom.
Q4. Explain how mucus and cilia in the airways reduce the chance of bacteria reaching the lungs.
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Mucus is sticky, so bacteria are trapped in it. Cilia move the mucus upwards, away from the lungs, so the trapped bacteria are carried out.
Q5. Explain why a cut in the skin makes infection more likely, and why swallowed bacteria are often destroyed.
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Unbroken skin is a barrier, and a cut breaks it, so pathogens can enter. Swallowed bacteria reach the stomach, where hydrochloric acid gives a very low pH that kills many of them.
Q6. Explain why the antibody made against one pathogen does not protect against a different pathogen.
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An antibody binds to one specific antigen. A different pathogen has different antigens, so the antibody does not fit.
Q7. The table shows antibody concentration after two exposures to the same pathogen. Data are invented.
| Day | Antibody concentration (arbitrary units) |
|---|---|
| 0 (first exposure) | 0 |
| 12 | 18 (peak) |
| 42 (second exposure) | 3 |
| 46 | 135 (peak) |
Compare the two responses using figures, and explain the difference.
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Time to peak: first 12 days, second 4 days (day 42 to day 46). Peak height: 18 and 135 units. 135 ÷ 18 = 7.5, so the second peak is 7.5 times higher. Check: 18 × 7.5 = 135.
Explanation: memory cells formed after the first exposure recognise the antigen quickly, so more antibodies are made sooner.
Q8. A class survey is invented. Among 500 vaccinated students, 5 caught a disease. Among 500 unvaccinated students, 40 caught it. Give both percentages and compare.
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Vaccinated: 5 ÷ 500 = 1%. Unvaccinated: 40 ÷ 500 = 8%. The unvaccinated group had 8 times the proportion of cases. Check: 1 × 8 = 8. Five vaccinated students still caught it, so the vaccine did not stop every case.
Q9. A student says: “This table proves the vaccine is the only reason the groups differ.” Suggest why this may be too strong.
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The table shows a difference but not its cause. The two groups may differ in age, earlier exposure or other factors. A careful statement says fewer vaccinated students caught the disease.
Q10. A culture has 500 bacteria, and 1 carries a resistance allele. An antibiotic kills all the non-resistant bacteria, and the survivor doubles every hour. How many bacteria are there after 6 hours, and what process explains this?
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6 doublings: 2⁶ = 64. Starting from 1, there are 64 bacteria. Check: 1, 2, 4, 8, 16, 32, 64.
The process is natural selection. The resistance allele was present by chance, the antibiotic selected for it, and the survivor reproduced and passed on the allele.
If you got these wrong
| Error type | Questions | Revisit |
|---|---|---|
| Mixed up pathogen, vector, route or symptom | Q1 to Q3 | Distinguish pathogen transmission from disease symptoms |
| Gave a name but no mechanism for a barrier | Q4, Q5 | Explain a barrier defence |
| Confused antibodies, antigens or memory cells | Q6, Q7 | Model an immune response at syllabus level |
| Over-claimed or skipped the percentages | Q8, Q9 | Interpret vaccination evidence descriptively |
| Said bacteria adapted or got used to it | Q10 | Discuss antimicrobial resistance without treatment advice |
After revisiting a lesson, try the matching question again a few days later without looking at the answer.
Where to go next
Return to the topic overview for the whole study route. Students who want a teacher to check their written explanations question by question can see how we work in online one-to-one Biology tuition.