Cambridge International AS & A Level Biology 9700: Immunity (by subtopic) – 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 topic 11, Immunity, of the Cambridge International AS & A Level Biology 9700 syllabus for examination in 2025, 2026 and 2027, outcome by outcome: sub-topic 11.1 The immune system (outcomes 1–4) and sub-topic 11.2 Antibodies and vaccination (outcomes 1–6). It is AS Level content, examined on Papers 1 and 2, and Paper 4 can assume it. Calculators are allowed in all 9700 papers.

Revise first with the immunity study guide and revision notes. The topic-level immunity practice questions are a separate set.

Questions

1. (11.1.1) Neutrophils and macrophages are both phagocytes.

(a) State two ways in which the role of a macrophage differs from that of a neutrophil. [2] (b) Neutrophils contain very large numbers of lysosomes. Explain why. [2]

2. (11.1.2) A patient receives a kidney from an unrelated donor.

(a) Explain what is meant by an antigen. [2] (b) Explain why the patient’s lymphocytes respond to cells of the transplanted kidney but not to the patient’s own cells. [3]

3. (11.1.3) These events in a primary immune response to a virus are in the wrong order.

• A: B-lymphocytes divide by mitosis.
• B: A macrophage engulfs the virus and displays its antigens.
• C: Plasma cells secrete antibodies.
• D: A T-helper cell with a complementary receptor binds to the displayed antigen.
• E: T-helper cells divide and release cytokines.
• F: B-lymphocytes differentiate into plasma cells.

(a) Write the letters in the correct order. [3] (b) Some viruses pass directly from one host cell to the next. Explain why T-killer cells, rather than antibodies, are needed to stop them. [2]

4. (11.1.3) A single B-lymphocyte is selected by an antigen. Assume it and all its descendants divide by mitosis every 12 hours.

(a) Calculate the number of cells in the clone after 4 days. [2] (b) 75% of these cells become plasma cells, each secreting 2000 antibody molecules per second. Calculate the number of antibody molecules secreted in one hour, in standard form to 3 significant figures. [2]

5. (11.1.4) A person was injected with harmless antigen X on day 0. On day 28 they were injected with X again and with a different antigen, Y, for the first time. The table shows antibody concentrations in their blood.

Day	0	7	14	21	28	31	35	42	49
Anti-X / arbitrary units	0	2	12	6	3	45	160	120	70
Anti-Y / arbitrary units	–	–	–	–	0	0	2	12	6

(a) Calculate how many times greater the peak of anti-X after day 28 is than the peak of anti-Y. [1] (b) Compare the response to X after day 28 with the response to Y. Use figures from the table. [3] (c) Explain these differences. [3] (d) Explain why the injection of X on day 0 did not speed up the response to Y. [1]

6. (11.2.1) Antibodies against measles virus do not bind to chickenpox virus.

(a) Explain why, with reference to antibody structure. [2] (b) A scientist makes a modified antibody with only one antigen-binding site. Suggest why it would be less effective at helping phagocytes destroy bacteria. [2]

7. (11.2.2) Monoclonal antibodies are made by the hybridoma method.

(a) Outline the hybridoma method. [4] (b) After fusion, cells are grown separately and only some are kept. Explain why. [2]

8. (11.2.3) Monoclonal antibodies are used in diagnosis and treatment.

(a) A rapid test detects a protein released by a pathogen into the blood. Blood flows along a strip carrying monoclonal antibodies attached to a coloured marker. Outline the principle of this test. [3] (b) Some cancer cells carry very large numbers of one receptor protein. A monoclonal antibody against this receptor is used as a treatment. Suggest why it harms healthy cells less than a drug that kills all dividing cells. [2] (c) Suggest why repeated doses of a mouse monoclonal antibody become less effective. [2]

9. (11.2.4) A person with a deep, dirty wound has never been vaccinated against tetanus. A doctor injects antibodies against tetanus toxin and gives a first dose of tetanus vaccine at the same visit.

(a) Name the type of immunity each injection gives, and explain why both are given. [4] (b) Name the type of immunity gained by recovering from an infection, and state how it differs from the immunity the vaccine gives. [2]

10. (11.2.5) A vaccine contains one purified protein from the surface of a virus, and no viral genetic material.

(a) Explain how this vaccine gives long-term immunity although it cannot cause infection. [4] (b) A second dose is given six months later. Explain the benefit. [2]

11. (11.2.6) The table shows data for one disease in a region where a vaccination programme began in 2000. Infants are too young to be vaccinated.

Year	2000	2005	2010	2015
Children vaccinated / %	40	70	92	95
Total cases	3600	1150	90	12
Cases in infants	410	160	9	2

(a) Calculate the percentage decrease in total cases between 2000 and 2015. [2] (b) Explain why cases in infants fell, although infants were not vaccinated. [3] (c) Suggest two reasons why the disease has not been eradicated from the region. [2]

Answers

1. (a) Macrophages present antigens to lymphocytes [1]; macrophages are long-lived, while neutrophils die after phagocytosis (or: neutrophils arrive first, in large numbers) [1]. (b) Lysosomes contain hydrolytic enzymes that digest engulfed pathogens [1]; each neutrophil engulfs many pathogens, so needs many lysosomes to fuse with phagocytic vacuoles [1]. Examiner insight: “Macrophages are bigger” gains nothing in (a): a role is asked for.

2. (a) A molecule, usually a protein or glycoprotein [1], that is recognised by the immune system and stimulates an immune response [1]. (b) Lymphocytes do not respond to self antigens on the patient’s own cells [1]; donor cells carry different, non-self antigens [1]; lymphocytes with complementary receptors bind these and are activated [1]. Examiner insight: “A foreign molecule” alone earns one mark at most in (a): self antigens are antigens too.

3. (a) B, D, E, A, F, C [3]. (Two marks if one adjacent pair is swapped; one mark if B is first and C last.) (b) Antibodies act in blood and tissue fluid and cannot enter host cells [1]; T-killer cells destroy infected cells displaying viral antigens, removing the cells where the virus replicates [1]. Examiner insight: “T-killer cells kill the virus” is not credited; they kill infected cells.

4. (a) 96 hours ÷ 12 = 8 divisions [1]; 2⁸ = 256 cells [1]. (b) 0.75 × 256 = 192; 192 × 2000 × 3600 [1] = 1.38 × 10⁹ molecules [1]. Examiner insight: Error carried forward is allowed in (b) from a wrong (a); using 8 × 2 instead of 2⁸ loses the (a) accuracy mark.

5. (a) 160 ÷ 12 = 13.3 times [1]. (b) Anti-X rises sooner: 45 AU on day 31 while anti-Y is still 0 [1]; anti-X peaks 7 days after injection, anti-Y after 14 days [1]; the anti-X peak is much higher, 160 AU against 12 AU (or: 70 AU against 6 AU on day 49) [1]. (c) The day 0 injection caused a primary response that left memory cells specific to X [1]; on day 28 these many memory B-cells recognised X at once, with no delay selecting a few matching lymphocytes [1]; they rapidly divided and formed many plasma cells (a secondary response), while Y caused only a primary response [1]. (d) Memory cells are specific: memory cells for X have receptors complementary to X, not to Y [1]. Examiner insight: Each comparison in (b) needs paired figures for both antigens.

6. (a) The variable regions form an antigen-binding site with a shape complementary to the measles antigen [1]; chickenpox antigens have a different shape, so they cannot bind [1]. (b) It binds only one bacterium, so cannot link bacteria together (agglutination) [1]; clumped bacteria are easier for phagocytes to engulf, so more would stay free [1]. Examiner insight: “The antibody is specific” repeats the stem; credit needs variable region, shape and complementary.

7. (a) A mouse is injected with the antigen [1]; B-lymphocytes making the matching antibody are removed from its spleen [1]; they are fused with myeloma (cancer) cells to form hybridoma cells [1]; the hybridoma making the required antibody is cloned in culture and the antibody collected [1]. (b) The spleen contains B-lymphocytes making many different antibodies, so many different hybridomas form [1]; only a clone of the cell making the required antibody gives a monoclonal antibody [1]. Examiner insight: The fusion mark needs myeloma (or cancer) cells named, not just “another cell”.

8. (a) The antibody binds only to the pathogen’s protein [1]; antibody–antigen complexes build up at one place on the strip [1]; the coloured marker shows there, so a line appears only if the pathogen is present [1]. (b) The antibody binds only to cells carrying that receptor, mainly cancer cells [1]; healthy dividing cells have few of these receptors, so are not targeted [1]. (c) Mouse antibodies are non-self antigens in humans [1]; the patient makes antibodies against the mouse antibody, which remove later doses [1]. Examiner insight: Without “binds only to this antigen”, (a) does not state the principle.

9. (a) The antibody injection gives artificial passive immunity [1]; the vaccine gives artificial active immunity [1]. The antibodies act at once on the toxin; the vaccine’s primary response takes days [1]. Injected antibodies are broken down and no memory cells form, so the vaccine is needed for long-term protection [1]. (b) Natural active immunity [1]; the antigen enters by infection, not by deliberate medical injection (both make memory cells) [1]. Examiner insight: Each type needs both words; “passive” alone does not score.

10. (a) The protein is a non-self antigen [1]; it activates matching T-helper cells and B-lymphocytes (clonal selection) [1]; this primary response produces plasma cells and memory cells [1]; if the virus enters later, memory cells give a fast secondary response that destroys it before symptoms develop [1]. (b) It causes a secondary response [1] that produces more memory cells, so immunity is stronger and longer-lasting [1]. Examiner insight: Saying the vaccine contains antibodies loses the first mark in (a).

11. (a) (3600 − 12) ÷ 3600 × 100 [1] = 99.7% [1]. (b) With 95% vaccinated, most people were immune [1], so there were few infectious people to pass on the pathogen [1]; so infants rarely met an infected person (herd immunity) [1]. (c) About 5% of children are not vaccinated and infants cannot be, so the pathogen can still spread [1]; cases can be brought in from other regions (or: the vaccine does not work in everyone, e.g. immunosuppressed people) [1]. Examiner insight: Dividing by the 2015 value is the usual error in (a); divide by the original value. Allow 99.67%.

Where marks are usually lost

• Defining an antigen as just “a foreign molecule”.
• Saying T-killer cells kill viruses, or that T-helper cells make antibodies.
• Leaving out myeloma cells, or the selection step, from the hybridoma method.
• Writing “passive” without “artificial” or “natural”.

Next steps

• Re-read the immunity revision notes and study guide.
• Try the topic-level immunity practice questions.
• Revisit topic 10: infectious diseases study guide.
• See the 9700 course hub and printable checklist.
• Take the 9700 AS diagnostic or all free 10-minute diagnostics.
• Book a free trial class.

Official syllabus

Cambridge International AS & A Level Biology 9700 syllabus for examination in 2025, 2026 and 2027, Version 1 (published September 2022), Cambridge University Press & Assessment. Topic 11 Immunity, sub-topics 11.1 and 11.2.