IGCSE Biology: Diseases and Immunity Practice Questions
A pathogen is a disease causing organism. The body defends itself with mechanical and chemical barriers, phagocytes that engulf pathogens, and lymphocytes that produce antibodies specific to the antigens on a particular pathogen.
Topic 10 of Cambridge IGCSE Biology 0610 rewards precision about antigens, antibodies and memory cells. Vaccination questions in particular follow a fixed sequence that Cambridge marks step by step. The questions below cover the defences, the immune response and the cholera example.
What you need to know for Diseases and Immunity
- PathogenA disease causing organism, such as a bacterium, virus, fungus or protoctist. A transmissible disease is one in which the pathogen can pass from one host to another.
- Mechanical and chemical barriersSkin forms a physical barrier. Hairs in the nose trap particles. Mucus traps pathogens and cilia sweep it away. Stomach acid kills many pathogens in swallowed food.
- PhagocytesWhite blood cells that engulf and digest pathogens. They are not specific to one pathogen.
- Lymphocytes and antibodiesLymphocytes produce antibodies, which are proteins with a shape complementary to a specific antigen on the pathogen surface. Antibodies cause pathogens to clump together and mark them for destruction.
- Active and passive immunityActive immunity comes from making your own antibodies after infection or vaccination, and is long lasting because memory cells are produced. Passive immunity comes from receiving ready made antibodies, for example through breast milk, and is short lived.
- CholeraCaused by a bacterium spread through contaminated water. The bacterium produces a toxin that causes chloride ions to be secreted into the small intestine, so water moves out of the cells by osmosis, causing severe watery diarrhoea and dehydration.
IGCSE Biology Diseases and Immunity questions and answers
4 exam-style questions written to the 0610 syllabus. Try each one on paper first, then open the worked answer to check your method against the marks.
Explain how a vaccination gives long term protection against a disease.
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- The vaccine contains a weakened, dead or modified form of the pathogen, or its antigens.
- These antigens are recognised by lymphocytes as foreign.
- The lymphocytes divide and produce antibodies with a shape complementary to the antigen, without the person suffering the disease.
- Some of these lymphocytes remain in the body as memory cells.
- If the real pathogen enters later, the memory cells recognise the antigen and produce large quantities of the specific antibody very quickly, destroying the pathogen before symptoms develop.
State two differences between active immunity and passive immunity.
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- Difference 1, source of antibodies: in active immunity the person's own lymphocytes produce the antibodies. In passive immunity the antibodies are received ready made, for example from the mother through the placenta or breast milk.
- Difference 2, duration: active immunity is long lasting because memory cells are produced. Passive immunity is short lived because no memory cells are formed and the antibodies are broken down.
- A third acceptable difference: active immunity takes time to develop, while passive immunity gives immediate protection.
Explain how the cholera bacterium causes the severe diarrhoea associated with the disease.
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- Cholera bacteria are swallowed in contaminated water and reach the small intestine.
- They produce a toxin that acts on the cells lining the small intestine.
- The toxin causes chloride ions to be secreted from the cells into the lumen of the intestine, lowering the water potential there.
- Water then moves out of the cells and into the intestine by osmosis, producing severe watery diarrhoea and rapid dehydration.
Describe three ways the body prevents pathogens from entering, before any immune response is needed.
Show the worked answer
- The skin forms a continuous physical barrier that pathogens cannot easily cross when it is intact.
- Mucus in the nose and airways traps pathogens, and cilia sweep the mucus away from the lungs to be swallowed.
- Hydrochloric acid in the stomach kills most pathogens in swallowed food, drink and mucus.
- Hairs in the nose also trap larger particles before they reach the airways.
Common mistakes in this topic
- Confusing antigen with antibody. Antigens are on the pathogen. Antibodies are made by lymphocytes.
- Saying vaccines contain antibodies.
- Describing phagocytes as specific. Phagocytes engulf any pathogen. Only the antibody response is specific.
- Writing that antibiotics kill viruses. Antibiotics act on bacteria only.
- Forgetting that passive immunity gives no memory cells and therefore no long term protection.
Exam tips
- Learn the vaccination sequence as five steps and write them in order. Cambridge marks it step by step.
- Use the phrase complementary shape when describing how an antibody binds an antigen.
- In graph questions on a second exposure, point out that the response is faster, larger and lasts longer. All three earn marks.
- Remember that herd immunity means enough people are vaccinated that the pathogen cannot spread easily, protecting those who are not immune.
- For any disease example, be ready to state the pathogen type, method of transmission, symptoms and one method of control.
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Diseases and Immunity FAQs
What is the difference between an antigen and an antibody?
An antigen is a molecule on the surface of a pathogen that the immune system recognises as foreign. An antibody is a protein produced by lymphocytes with a shape complementary to a specific antigen. Antibodies bind to antigens, causing pathogens to clump together and marking them for destruction.
How does a vaccine work?
A vaccine introduces weakened, dead or modified pathogens, or their antigens, into the body. Lymphocytes recognise the antigens and produce specific antibodies without the person becoming ill. Memory cells remain afterwards, so if the real pathogen is met later, antibodies are produced far more quickly and in larger amounts.
What is the difference between active and passive immunity?
Active immunity is protection from producing your own antibodies after an infection or a vaccination. It develops slowly but lasts a long time because memory cells are formed. Passive immunity is protection from receiving ready made antibodies, such as through breast milk. It works immediately but is short lived.
Why do antibiotics not work against viruses?
Antibiotics work by disrupting structures and processes found in bacterial cells, such as the bacterial cell wall. Viruses have no cell wall and no metabolism of their own, reproducing inside host cells instead, so there is nothing for an antibiotic to act on.
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Written to the published Cambridge IGCSE Biology (0610) syllabus. Check your school entry code and syllabus year, because Core and Extended candidates are assessed on different content. Last reviewed 2026-08-12.