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S5 Biology: Immune Response and Vaccines – Practice Paper 2 (Intermediate, 10 Questions)
S5 Biology: Immune Response and Vaccines – Practice Paper 2 (Intermediate, 10 Questions)
Paper two moves to the cellular level: antigen presentation, helper T cell cytokines and B cell differentiation, together with antibody structure, titre and herd immunity calculations. Every item asks which cell performs which step.
Quick answer Antigen-presenting cells display antigen to helper T cells, whose cytokines stimulate B cells; an antibody has two heavy and two light chains, four in all; 800 against 100 is eight times; the titre is 1:40; an R0 of 5 needs 80%; interferon is second line; only plasma cells secrete antibody.
01 Paper details (check answers afterwards)
| Item | Detail |
|---|---|
| Questions | 10 questions |
| Suggested time | about 25 minutes |
| Difficulty mix | Foundation 2 · Intermediate 3 · Challenge 3 · Error redo 2 |
| Chapter | Chapter: S5 Biology | Immune Response and Vaccines: Specific Immunity, Memory Cells and Herd Immunity |
| Level | Intermediate |
02 Questions (10 items)
- FoundationIn specific immunity what role do antigen-presenting cells such as macrophages play?
- FoundationHow do helper T cells assist B cells?
- IntermediateWhat is the basic structure of an antibody molecule?
- IntermediateAntibody peaks at about 800 units on a second infection against about 100 units on the first: how many times higher is the second peak?
- IntermediateSerum still shows antibody at a 1:40 dilution but not at 1:80: what is the antibody titre?
- ChallengeA disease has an R0 of 5: what minimum fraction of the population must be immune for herd immunity?
- ChallengeWhy do some vaccines need two doses?
- ChallengeWhich line of defence does interferon belong to and how does it act?
- Error redoError retry: a student believes T lymphocytes secrete antibody directly. What is correct?
- Error redoError retry: a student calls antivenom serum active immunity. Why is that wrong?
03 Answers and one-line notes
| # | Answer | One-line note |
|---|---|---|
| 1 | They engulf the pathogen and display antigen fragments on their surface to helper T cells, which starts the specific response | Without presentation the T cells never see the antigen at all. |
| 2 | After recognising antigen they release cytokines that stimulate antigen-bound B cells to divide into plasma cells and memory B cells | T cells coordinate the response and do not produce antibody themselves. |
| 3 | Two heavy chains plus two light chains, four polypeptide chains in all, forming a Y shape, with the variable regions binding the antigen specifically | Two heavy and two light chains make four in total, and the variable regions set the specificity. |
| 4 | Eight times higher | 800 divided by 100 is 8, which is what memory cells buy. |
| 5 | 1:40, that is a titre of 40 | The titre is the last dilution that still tests positive. |
| 6 | 80% | One minus one fifth is 0.8, and the higher the R0 the higher the fraction needed. |
| 7 | The first dose builds the primary response and memory cells; the second, a booster, triggers a secondary response that raises antibody levels and memory cell numbers higher and for longer | The second dose does not repeat the first, it wakes the memory cells up. |
| 8 | The second line, a non-specific defence: infected cells secrete interferon, which makes neighbouring cells suppress viral replication | Interferon protects the neighbours rather than the cell already infected. |
| 9 | Only plasma cells secrete antibody; helper T cells coordinate the response and cytotoxic T cells kill infected cells | Mixing up the coordinator with the producer is a common way to lose marks. |
| 10 | The serum supplies ready-made antibodies and the body makes none of its own, so it is artificially acquired passive immunity that protects at once but only briefly | Immediate protection is the signature of passive immunity and also why it fades. |
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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