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S5 Biology: Immune Response and Vaccines – Practice Paper 4 (Error Correction, 10 Questions)
S5 Biology: Immune Response and Vaccines – Practice Paper 4 (Error Correction, 10 Questions)
Paper four targets the boundaries that cost marks in the first three papers: how the first line works, the division of labour between plasma cells and T cells, a vaccine carrying antigen rather than antibody, the recipient of antigen presentation, the four chains of an antibody, plus dilution, herd immunity threshold and half-life calculations. The last item takes apart the classic claim that serum treatment is active immunity.
Quick answer Skin and mucosa form the first line; plasma cells secrete antibody; a vaccine carries antigen and needs one to two weeks for protection; 25 out of 500 is 5%; antigen is presented to helper T cells; an antibody has two heavy and two light chains with two binding sites; 20 times 4 gives a 1:80 dilution; an R0 of 6 needs about 83.3%; 800 falling to 200 is two half-lives; antivenom is passive immunity.
01 Paper details (check answers afterwards)
| Item | Detail |
|---|---|
| Questions | 10 questions |
| Suggested time | about 25 minutes |
| Difficulty mix | Foundation 4 · Intermediate 3 · Challenge 2 · Error redo 1 |
| Chapter | Chapter: S5 Biology | Immune Response and Vaccines: Specific Immunity, Memory Cells and Herd Immunity |
| Level | Error Correction |
02 Questions (10 items)
- FoundationWhich line of defence do skin and mucous membranes belong to, and how do they keep pathogens out?
- FoundationIn specific immunity, which cell secretes antibody, and what do T cells do?
- FoundationWhat does a vaccine usually contain, and why is a person not protected on the day of injection?
- FoundationIn a school of 500 students, 25 were infected in a flu outbreak. What is the infection rate?
- IntermediateWhich cell receives processed antigen from an antigen-presenting cell, and what follows?
- IntermediateHow many polypeptide chains make up one antibody molecule, and which part binds antigen?
- IntermediateA serum is diluted 1:20 and that dilution is then diluted 1:4. What is the overall dilution?
- ChallengeA disease has an R0 of 6. What minimum fraction of the population must be immune for herd immunity?
- ChallengeAntibody concentration falls from 800 units to 200 units. How many half-lives have passed?
- Error redoA student says antivenom contains antibody and is therefore active immunity. What is wrong?
03 Answers and one-line notes
| # | Answer | One-line note |
|---|---|---|
| 1 | The first line; intact keratin is a physical barrier, sweat and sebum are mildly acidic, and mucus with cilia traps pathogens and sweeps them away | The first line does not tell pathogens apart and blocks rather than destroys them. |
| 2 | Plasma cells secrete antibody, and a plasma cell comes from a B lymphocyte stimulated by antigen; T cells recognise antigen, help other cells or kill infected cells, and do not secrete antibody | Splitting recognition from antibody production between two cell types is the line examiners test most. |
| 3 | It contains antigen, such as an attenuated or killed pathogen, a toxin or an antigen fragment; the body needs about one to two weeks to make enough antibody and memory cells, so protection is not immediate | A vaccine delivers antigen, not ready-made antibody, so the body has to build the protection itself. |
| 4 | 25 divided by 500 is 0.05, that is 5% | Write the denominator as the 500 students first, not the 25 cases. |
| 5 | A helper T cell receives it; once stimulated the helper T cell releases cytokines that drive B cells to become plasma cells and help activate cytotoxic T cells | Antigen presentation bridges innate and specific immunity, and the helper T cell is the pivot. |
| 6 | Four, two heavy chains plus two light chains; the antigen-binding site in the variable region does the binding, so one antibody has two sites | Remember two plus two makes four chains and two binding sites, and the structure item is secure. |
| 7 | 20 times 4 is 80, so the overall dilution is 1:80 | Stepwise dilutions multiply rather than add. |
| 8 | One minus one sixth is about 0.833, that is roughly 83.3% | The larger the R0, the closer the required fraction gets to 100%, so herd immunity is harder to reach. |
| 9 | Two: 800 halves to 400, and 400 halves to 200 | A half-life halves the amount each time, so two halvings mean two half-lives. |
| 10 | The active and passive boundary is wrong; antivenom puts ready-made foreign antibody into the body without the body making any, so it is artificial passive immunity, immediate but short-lived and with no memory cells | Anything that supplies ready-made antibody is passive, including maternal antibody and serum treatment. |
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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