A Level Biology: Immunity — Practice Questions (Cambridge 9700)

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 — Cambridge International holds copyright in its own papers. Use these alongside the official past papers available from your board.

Each question practises a skill tested in the June 2024 Paper 22. After each answer there is an examiner insight, a mark-scheme insight or a tip and, where one matches, the real question to try next.

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Questions

1. A neutrophil in the skin detects bacteria that have entered through a cut.

(a) Outline the events that lead to the bacteria being enclosed in a phagocytic vacuole.

(b) Name the organelles that then fuse with the vacuole and release hydrolytic enzymes. [4]

2. One type of polio vaccine contains live polioviruses of a weakened (attenuated) strain and is given as a few drops into the mouth, rather than by injection. Poliovirus normally enters the body through the gut. Suggest and explain the advantages of these features of the vaccine. [4]

3. A person was vaccinated against a disease eight years ago. The concentration of antibodies against this pathogen in their blood is now close to zero, but they do not become ill when they are exposed to the pathogen. Explain why. [3]

4. State whether each of these gives active or passive immunity, and whether it is natural or artificial:

(a) a baby receiving antibodies in breast milk

(b) a person recovering from measles

(c) a person bitten by a snake being given an injection of antibodies against the venom

(d) a child being given a vaccine. [4]

5. Explain why a person with HIV/AIDS produces fewer antibodies when infected by a new pathogen. [3]

6. Describe how the structure of an antibody molecule is related to its function. [3]

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Answers

1. (a) Any three: the neutrophil moves towards the bacteria by chemotaxis, following chemicals released by the bacteria or damaged cells [1]; antigens on the bacteria bind to receptors on the neutrophil’s cell surface membrane (binding is helped if antibodies have attached to the bacteria) [1]; the cell surface membrane extends as pseudopodia around the bacteria and engulfs them (endocytosis) [1]; the membrane fuses and the vacuole pinches off into the cytoplasm [1].

(b) Lysosomes [1].

Examiner insight (Cambridge 9700 June 2024 examiner report, Paper 22, Question 2(b)): Full credit needed an event before or after engulfing, such as receptor binding or the membrane fusing. Repeating that the cell “detected” the bacteria was not enough, because the question already said so. Events after the vacuole formed, or accounts of lymphocytes, gained nothing. “Lysosome” had to be spelled correctly.

Source for the examiner insights on this page: Cambridge International AS & A Level Biology 9700 June 2024 Principal Examiner Report for Teachers, Paper 9700/22 section, paraphrased.

Try the real question next: Cambridge International AS & A Level Biology 9700, June 2024, Paper 22, Question 2(b).

2. Any four: the live viruses replicate in the body, so there is a large amount of non-self antigen [1]; this gives a strong primary immune response, making many memory cells [1]; this is artificial active immunity, which is long-lasting [1]; because the strain is weakened, it almost never causes the disease [1]; the vaccine stimulates an immune response in the gut, where poliovirus enters, so the virus can be stopped before it spreads through the body [1]; giving it by mouth needs no needles or specially trained staff, so it is quick, cheap and easy to give to large numbers of people (and avoids fear of injections) [1].

Examiner insight (Cambridge 9700 June 2024 examiner report, Paper 22, Question 2(c)): In the question on a live vaccine, some answers described the advantages of a vaccination programme instead of the stated features of the vaccine itself. Good answers explained that memory cells are made during the primary response, and did not just say the body “has memory cells”.

Try the real question next: Cambridge International AS & A Level Biology 9700, June 2024, Paper 22, Question 2(c).

3. The vaccine caused a primary immune response that produced memory cells (memory B- and T-lymphocytes), which stay in the body for many years after the antibodies have gone [1]. When the pathogen enters, memory cells recognise its antigen and cause a secondary immune response, which is faster and larger [1]. Plasma cells quickly make large amounts of antibody, so the pathogen is destroyed before it can cause symptoms [1].

Examiner insight (Cambridge 9700 June 2024 examiner report, Paper 22, Question 2(c)): Examiners wanted precise terms, not phrases such as memory cells “remembering” or “fighting” the infection. Some answers wrongly treated antibodies as memory cells, or said antibodies stay in the blood ready for a later infection.

Try the real question next: Cambridge International AS & A Level Biology 9700, June 2024, Paper 22, Question 2(c).

4. (a) Natural passive [1].

(b) Natural active [1].

(c) Artificial passive [1].

(d) Artificial active [1].

Mark-scheme insight (Cambridge 9700 June 2024 mark scheme, Paper 22, Question 2(c)): A vaccine was credited as giving (artificial) active immunity, and “natural active immunity” was rejected. Being given antibodies is passive; making your own antibodies is active.

Source for the mark-scheme insights on this page: Cambridge International AS & A Level Biology 9700 June 2024 mark scheme for Paper 22 (9700/22), paraphrased. Cambridge’s 9700 past papers page publishes the Paper 21 mark scheme from this series, not the Paper 22 one.

Try the real question next: Cambridge International AS & A Level Biology 9700, June 2024, Paper 22, Question 2(c).

5. HIV infects and destroys T-helper lymphocytes [1]. T-helper cells normally release cytokines that stimulate B-lymphocytes with the matching receptor to divide and become plasma cells [1]. With few T-helper cells, fewer B-lymphocytes are activated, so fewer plasma cells form and less antibody is made [1].

Tip: Name the cell HIV destroys, then follow the chain step by step until you reach antibodies.

6. Any three: made of four polypeptide chains (two heavy, two light) held by disulfide bonds [1]; the variable regions at the tips form antigen-binding sites with a shape complementary to one specific antigen [1]; there are two binding sites, so antibodies can bind two pathogens and clump them together (agglutination) [1]; the constant region binds to receptors on phagocytes [1]; the hinge region gives flexibility so both sites can bind antigens at different distances apart [1].

Tip: Link every structural feature to what it allows the antibody to do. A list of parts alone rarely gains full marks.

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Where marks are usually lost

• Repeating information given in the question (such as “detects the bacteria”) instead of describing a new step.
• Writing about vaccination programmes when the question asks about the features of a vaccine.
• Saying antibodies act as memory cells, or that antibodies stay in the blood for years.
• Describing memory cells as “remembering” or “fighting” rather than naming the secondary immune response.
• Mixing up natural/artificial with active/passive immunity.