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S5 Biology: Immune Response and Vaccines – Practice Paper 3 (Challenge, 10 Questions)
S5 Biology: Immune Response and Vaccines – Practice Paper 3 (Challenge, 10 Questions)
Paper three handles real-world reasoning: the order of IgM and IgG, transplant matching, a broken cold chain, plus the herd immunity threshold, efficacy times coverage, antibody half-life and relative risk. Each of the four calculable items first asks which formula applies.
Quick answer IgM comes first and IgG later; MHC is the self marker; heat denatures the antigen; an R0 of 4 needs 75%, which is 7.5 million of ten million; 0.95 times 0.90 is 85.5%; three half-lives leave 12.5%; 2% against 5% gives a relative risk of 0.4.
01 Paper details (check answers afterwards)
| Item | Detail |
|---|---|
| Questions | 10 questions |
| Suggested time | about 30 minutes |
| Difficulty mix | Foundation 1 · Intermediate 2 · Challenge 4 · Error redo 3 |
| Chapter | Chapter: S5 Biology | Immune Response and Vaccines: Specific Immunity, Memory Cells and Herd Immunity |
| Level | Challenge |
02 Questions (10 items)
- FoundationIn a primary immune response which antibody class appears first and which then dominates?
- IntermediateWhy must tissue antigens be matched before an organ transplant?
- IntermediateHow does a break in the vaccine cold chain reduce efficacy?
- ChallengeA disease has an R0 of 4 in a population of 10 million: with a vaccine of 100% efficacy, how many people must be vaccinated for herd immunity?
- ChallengeA vaccine is 95% efficacious and 90% of people are vaccinated: what fraction of the population is effectively protected?
- ChallengeInjected antibodies have a half-life of about 21 days: what percentage remains after three half-lives?
- ChallengeDistrict A has 20 infections among 1,000 people and district B has 25 among 500: what is the relative risk of A against B?
- Error redoError retry: a student treats a viral infection with antibiotics and concludes vaccines do not work. What is wrong?
- Error redoError retry: an antibody peak rises from 100 to 800 and a student answers 700 times more. What is correct?
- Error redoError retry: a student assumes protection begins the moment a vaccine is given. What is correct?
03 Answers and one-line notes
| # | Answer | One-line note |
|---|---|---|
| 1 | IgM appears first and IgG takes over later; in a secondary response IgG dominates and arrives sooner | The order is IgM then IgG, first M and later G. |
| 2 | Tissue antigens, the MHC, are self markers on the cell surface; a mismatch is read by the recipient T cells as foreign antigen and triggers rejection | Rejection is at heart a specific immune response aimed at the graft. |
| 3 | Heat denatures the antigen protein, the shape of its epitopes changes, the immune system can no longer recognise the original antigen and antibody titres fall or the vaccine fails | It is the antigen rather than the antibody that denatures, and a changed shape no longer fits. |
| 4 | 7.5 million people | One minus one quarter is 75%, and 10,000,000 times 0.75 is 7,500,000. |
| 5 | 85.5% | 0.95 times 0.90 is 0.855, so efficacy and coverage multiply rather than add. |
| 6 | 12.5% | One half cubed is one eighth, or 12.5%, since each half-life halves what is left. |
| 7 | 0.4 | That is 2% against 5%, and 2% divided by 5% is 0.4, so A carries four tenths of the risk of B. |
| 8 | Antibiotics act only on bacteria and do nothing to viruses; a vaccine is preventive and works through memory cells shortening the secondary response, so the two mechanisms cannot disprove each other | Reading a treatment failure as proof against prevention swaps one claim for another. |
| 9 | It is 8 times higher, since 800 divided by 100 is 8; the 700 is an absolute difference rather than a ratio | A ratio says how many times as much and a difference says how much more, and the two cannot be mixed. |
| 10 | The primary response takes days to about two weeks to raise enough antibody and infection is still possible in between; protection settles only after the full course is completed | Vaccine protection is built over time rather than switched on by the injection. |
04 What to do after marking
- After marking, redo only the wrong items and write down which step went wrong (formula, unit, or misread number).
- Repeat the same item two days later; move to the next paper only when both attempts are correct.
- Parents only need the answer and note columns; there is no need to explain every item.
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