Diseases and immunity
Cambridge IGCSE Biology 0610 Topic 10 revision chapter covering diseases and immunity, tiered throughout into Core content for all candidates and Supplement content for Extended candidates. The split in this topic is the most lopsided in the syllabus - five Core statements against twelve Supplement ones - so the chapter runs as one continuous Core block followed by one continuous Supplement block, and labels every section, question and mistake-clinic entry with the tier it belongs to. The organising idea is a single chain of infection running from a pathogen in an infected host, along a route of transmission, past the body's defences, into a new host, and finally to an immune response that may or may not be ready; every measure taught in the chapter is attached to the link of that chain it breaks rather than presented as an item in a list, because the syllabus verb for control measures is explain rather than state. The Core half opens with the two definitions the topic rests on - a pathogen as a disease-causing organism, and a transmissible disease as one in which the pathogen can be passed from one host to another - and makes explicit that a disease with no pathogen cannot be transmissible however serious it is. Transmission is then separated into the two routes the syllabus names, with its own six examples: direct contact including blood and other body fluids, and indirect transmission from contaminated surfaces, contaminated food, animals and air, with the decision rule given as a single question about whether anything came in between, and the point made that the category follows the route described rather than the name of the disease. The body defences are taught strictly as the limited-to list of five - skin as a physical barrier, hairs in the nose filtering larger particles from inhaled air, mucus trapping pathogens and particles in the airways, acid conditions in the stomach destroying many swallowed pathogens, and white blood cells engulfing and digesting pathogens by phagocytosis and producing antibodies - each with its mechanism and its honest limit, and with cilia and blood clotting marked clearly as real defences that belong to other topics rather than to this one. The heaviest Core statement, controlling the spread of disease, is given its own section built on the five named measures: a clean water supply, hygienic food preparation, good personal hygiene, waste disposal and sewage treatment, each explained as an interruption to a specific step of transmission, with the faecal-oral route drawn as four lanes that can be cut at the source or near the mouth, and with the syllabus's own exclusion of the stages of sewage treatment stated plainly. The Supplement half builds the immune response in order: antigens as molecules with specific shapes belonging to the pathogen, antibodies as proteins whose binding sites are complementary to one particular antigen, and the two consequences of binding that the syllabus names - the direct destruction of the pathogen, or its marking for destruction by phagocytes, which then engulf and digest it. Active immunity is defined as defence by antibody production in the person's own body and given its two routes, infection and vaccination; vaccination is outlined in the three lettered stages the syllabus uses, with the fuller seven-step mechanism presented underneath them so that detail is never mistaken for extra mark points; memory cells are explained through a primary-against-secondary antibody graph drawn deliberately without numerical values; and the role of vaccination in controlling the spread of disease is explained at population level, as fewer susceptible hosts and more chains of transmission interrupted, with an explicit refusal of the overclaim that high coverage makes an unvaccinated person immune. Passive immunity is then set against all of that as the one kind of immunity a person does not build, acquired ready-made from another individual across the placenta and in breast milk, immediate but temporary because no memory cells are formed - the single statement from which every other difference follows. Cholera closes the chapter as the topic's only named disease, and a Supplement one: a bacterium transmitted in contaminated water, with the mechanism given as a fixed causal chain in which the toxin causes chloride ions to be secreted into the small intestine, the water potential of the lumen falls, water moves into the gut by osmosis, and severe watery diarrhoea causes dehydration and loss of ions from the blood. Because Topic 10 names no practical investigation, the practical section says so and trains instead the AO3 skill Papers 5 and 6 can reach here: describing a trend, quoting figures with units, calculating a percentage change, giving the biological mechanism, and separating an association from a causal claim the data alone cannot support.Show moreShow less
Revision notes
Interactive notes with exam tips and worked examples.
Study path
Chapter overview
A summary of this Biology chapter — open a section to read it. The full notes, worked examples and practice questions are in the study modules above.
What is Diseases and immunity about?
A pathogen is a disease-causing organism, and a transmissible disease is one in which the pathogen can be passed from one host to another. Every method of disease control in this chapter works by breaking one specific link in the chain that runs from an infected host, along a route of transmission, past the body's defences, into a new host. Name the link a measure breaks and you have explained the measure.
Key ideas to remember
- Pathogen, route, contact, entry, response. Five links — and disease control is nothing more than breaking one of them.
- If you can only remember one repair from this page, make it this: the pathogen owns the antigen, your lymphocyte makes the antibody, and your phagocyte does the eating. And on the Core side: name the step, never just the measure.
- Three lists, two chains, one diagram. That is the whole topic, and it fits on a single sheet of paper.
What you need to be able to do
- Core 10.1.1 Describe a pathogen as a disease-causing organism.
- Core 10.1.2 Describe a transmissible disease as one in which the pathogen can be passed from one host to another — and say why not every disease is transmissible.
- Core 10.1.3 State that a pathogen is transmitted directly, including through blood and other body fluids, or indirectly, including from contaminated surfaces, food, animals and air — and classify a described route into one of the two from the route itself.
- Core 10.1.4 Describe the body defences, limited to skin, hairs in the nose, mucus, stomach acid and white blood cells, naming the mechanism of each and stating honestly what it cannot do.
- Core 10.1.5 Explain the importance of a clean water supply, hygienic food preparation, good personal hygiene, waste disposal and sewage treatment in controlling the spread of disease — naming, for each, the step of transmission it interrupts.
- Supplement 10.1.6 Describe active immunity as defence against a pathogen by antibody production in the body.
- Supplement 10.1.7 State that each pathogen has its own antigens, which have specific shapes.
- Supplement 10.1.8 Describe antibodies as proteins that bind to antigens, leading either to the direct destruction of pathogens or to their being marked for destruction by phagocytes.
- Supplement 10.1.9 State that specific antibodies have complementary shapes which fit specific antigens.
- Supplement 10.1.10 Explain that active immunity is gained after an infection by a pathogen or by vaccination.
- Supplement 10.1.11 Outline the process of vaccination in its three stages: antigens in, lymphocytes respond and make antibodies, memory cells give long-term immunity — and read a primary-against-secondary antibody graph.
- Supplement 10.1.12 Explain the role of vaccination in controlling the spread of diseases, without overclaiming what it guarantees for any one person.
- Supplement 10.1.13 Explain passive immunity as short-term defence by antibodies acquired from another individual, including across the placenta and in breast milk.
- Supplement 10.1.14 Explain the importance of breast-feeding for the development of passive immunity in infants.
- Supplement 10.1.15 State that memory cells are not produced in passive immunity — and use that one fact to derive every other difference from active immunity.
- Supplement 10.1.16 Describe cholera as a disease caused by a bacterium transmitted in contaminated water.
- Supplement 10.1.17 Explain the cholera mechanism as one causal chain, in order: toxin → chloride ions secreted into the small intestine → osmotic movement of water into the gut → diarrhoea, dehydration and loss of ions from the blood.
Why Diseases and immunity matters
Why the loss of ions matters as much as the loss of water. Diarrhoea removes both. Replacing water alone would not restore the blood; the ions have to be replaced too, which is why rehydration solutions contain salts as well as water. Answers that mention only dehydration are describing half the problem.
Common mistakes to avoid
- Core 10.1.2 "Every disease is transmissible." Transmissible means a pathogen can pass from one host to another. Diseases caused by diet, by inherited alleles or by the body's own processes have no pathogen to pass. Write A transmissible disease is one in which the pathogen can be passed from one host to another; many diseases are not transmissible.
- Core 10.1.3 "The animal that carried it caused the disease." Whenever an animal appears in a transmission route, it is carrying the pathogen, not being it. An animal that carries a pathogen between hosts is a vector — a word the syllabus does not use, but the idea behind the animals route it does name. A vector transports; a pathogen causes. Write The disease is caused by a pathogen, which is transmitted indirectly from one host to another by an animal.
- Core 10.1.5 "Clean water controls the spread of disease." True, and worth nothing on its own. 10.1.5's verb is explain, so naming the measure is where the answer starts. The mark is for the step of transmission that the measure interrupts. Write Treated water contains no living pathogens, so people drinking it do not take pathogens into the body and the route through contaminated water is cut.
- Core 10.1.5 "Sewage treatment removes the solids, then the water passes through filter beds and settling tanks…" The syllabus says in the statement itself that details of the stages of sewage treatment are not required. Every sentence spent on them is a sentence not spent on the mark that was available. Write Sewage treatment keeps faecal material, and the pathogens in it, out of the water supply, so those pathogens never enter the route.
- Core 10.1.4 "The body's defences are skin, cilia, clotting, tears, sweat…" 10.1.4 is limited to five: skin, hairs in the nose, mucus, stomach acid and white blood cells. Cilia and clotting are real defences examined in other topics; anything else on that list is not being asked for here. Write Name the five, and give each one its mechanism — a physical barrier, filtering, trapping, chemical destruction, and engulfing and antibody production.
- Supplement 10.1.17 "Cholera diarrhoea happens because water is not absorbed." That describes a different and far milder situation. In cholera, water is actively drawn out of the blood and tissues into the gut. Write The toxin causes chloride ions to be secreted into the lumen; the water potential of the lumen falls; water moves in from the blood and tissues by osmosis.
- Supplement 10.1.17 "Cholera bacteria make holes in the intestine wall." The wall stays intact. What changes is what it transports. Write The bacteria produce a toxin that changes the movement of chloride ions across the intestinal cells.
- Supplement 10.1.8 "Antibodies engulf pathogens." Antibodies are proteins. A protein cannot surround and swallow anything. Phagocytes are cells, and they engulf. Write Antibodies are proteins that bind to antigens, leading either to the direct destruction of the pathogen, or to the pathogen being marked for destruction by phagocytes, which engulf and digest it. Those are the two outcomes 10.1.8 names, and they are the two to give. Clumping is real and it is what Figure 10.7 draws, but it is not one of the two.
- Supplement 10.1.8 "Phagocytes produce specific antibodies." Phagocytes are non-specific and do not produce antibodies. Lymphocytes do. Write Lymphocytes produce specific antibodies and form memory cells; phagocytes engulf and digest pathogens.
- Supplement 10.1.7 "Antigens are made by lymphocytes." Antigens belong to the pathogen. Lymphocytes make antibodies against them. Write An antigen is a molecule, usually on the pathogen's surface, that stimulates a specific immune response.
- Supplement 10.1.11 "Vaccination gives passive immunity." A vaccine supplies antigens, not antibodies, and your own lymphocytes do the work. Write Vaccination stimulates active immunity: the person's own lymphocytes produce antibodies and memory cells are formed.
- Supplement 10.1.11 "Vaccines always contain live pathogens." They may contain weakened pathogens, inactivated pathogens, or the antigens alone. Write A vaccine contains antigens from the pathogen, in a form that does not cause the disease.
- Supplement 10.1.15 "Passive immunity produces memory cells." The recipient's own lymphocytes never met the antigen, so there is nothing to remember. Write Passive immunity gives immediate protection but no memory cells are formed, so protection is short-term.
- Supplement 10.1.14 "Breast milk gives a baby permanent immunity." The antibodies are received, not made, and they are broken down over time. Write Antibodies in breast milk give passive immunity: immediate but temporary protection while the infant's own immune system is developing.
- Supplement 10.1.12 "If enough people are vaccinated, nobody can catch the disease." High coverage reduces transmission. It does not make an unvaccinated person immune, and it does not guarantee zero transmission. Write High vaccination coverage reduces the number of susceptible hosts, so chains of transmission are interrupted more often, indirectly protecting some people who cannot be vaccinated.
- Core 10.1.4 "Skin and mucus stop all pathogens getting in." If they did, nobody would ever be ill. Barriers reduce entry; they do not prevent it. Write First-line barriers reduce the number of pathogens that enter the body, but they do not prevent all infection.
Examiner tips
- Where the tiering bites in Topic 10. The split is not scattered: it is a clean break. Statements 1 to 5 are Core and 6 to 17 are Supplement, with nothing interleaved. So this chapter runs as one continuous Core block — sections A to D — and then one continuous Supplement block, sections E to M. You will not find a Supplement paragraph hiding in the middle of a Core section, and you will not find a Core sentence you need trapped inside a Supplement block.
How Diseases and immunity is examined
- This topic is unusual: none of it is calculation, and almost all of it is sequence. The syllabus statements themselves are written as chains — 10.1.17 fixes its own causal order, and 10.1.11 sets out three lettered stages — so an answer that carries the right vocabulary in the wrong order has not given the statement the syllabus asks for.
- The syllabus verb is describe or explain, and the definition is the whole answer. Pathogen, transmissible disease, active immunity and passive immunity all have syllabus wording. Learn them as sentences, not as ideas you will assemble on the day.
- A described situation, and you decide direct or indirect and justify it from the route. 10.1.3 is a statement about routes, not about diseases, so a memorised list of diseases will not settle it — read what the pathogen actually did.
- The longest answers in the topic. Cholera and vaccination are the Supplement mechanisms; the five named controls are the Core one. Each is a numbered chain in this chapter. Write it as a chain, in order.
- Describe the trend, quote figures with units, then be careful: association is not proof of cause. That last step is the one most easily left out.
- Command word watch. State and describe want the observation. Outline — 10.1.11's own verb — wants the main stages in order, not every detail. Explain wants the reason, and in this topic the reason is almost always a mechanism with at least three linked steps. Suggest means the answer is not printed anywhere in this chapter: you are being asked to apply the chain to an unfamiliar situation.
Frequently asked questions
Is a virus a living organism, and does that matter for the definition of a pathogen?
For the purposes of this syllabus, treat a virus as a pathogen. The definition you are given is "a disease-causing organism", and viruses cause transmissible diseases. The debate about whether viruses are alive is not examined anywhere in this topic, and the definition does not ask you to resolve it: it asks what the organism does. What a virus is made of — genetic material in a protein coat, able to reproduce only inside a host cell — belongs to Topic 1, not here.
Cholera is Supplement. Do I need it?
Only if you are an Extended candidate. Both cholera statements — 10.1.16 and 10.1.17 — appear in the Supplement column of the syllabus table, so a Core candidate is not examined on cholera at all, and nothing in the Core half of this topic depends on it. If you are on the Core route, your topic finishes at the end of section D. If you are on the Extended route, cholera is the only named disease in Topic 10, and 10.1.17 is one of only two statements in the topic that carry a full mechanism — so it is worth more of your time than its two statements suggest.
Why are cilia not on the list of body defences?
Because 10.1.4 says limited to, and it lists five things: skin, hairs in the nose, mucus, stomach acid and white blood cells. Cilia are a genuine defence and they are examined — in Topic 11, at Supplement level, where the statement is about goblet cells, mucus and ciliated cells protecting the breathing system. In an answer to "describe the body defences" in this topic, name the five. Mentioning that the mucus is swept away does your answer no harm, but it is not one of the five — so if you give cilia instead of one of them, you have given four. The same applies to blood clotting, which is Core content in Topic 9.
If a vaccine contains the pathogen, why does it not give you the disease?
Because of the form it is in. A vaccine may contain weakened pathogens, inactivated pathogens, or just the antigens, and none of these can establish a normal infection. What survives is the antigen's shape, which is all the lymphocytes need in order to produce complementary antibodies and form memory cells.
Why do some vaccines need booster doses if active immunity is long-term?
Because the syllabus word is "long-term", and long-term is not the same as permanent. For some pathogens the memory-cell response weakens over years, so a further dose is given to stimulate the response again. This is still active immunity: the person's own lymphocytes do the work each time.
Is passive immunity ever given deliberately?
Yes, ready-made antibodies can be given as a medical treatment when immediate protection is needed and there is no time to build a response. The syllabus examples you must know are the natural ones — antibodies crossing the placenta and antibodies in breast milk — and both share the same limitation: immediate protection, no memory cells, short duration.
How much detail about sewage treatment do I need?
None of the stages — the syllabus says so inside the statement itself. What you are asked for is that waste disposal and sewage treatment keep faecal material, and the pathogens in it, out of the water people drink and use, and that this breaks the faecal–oral route near its source. Describing settling tanks, filter beds and digesters answers a question the syllabus explicitly does not ask, and costs you the time the explanation needed.
Can I say "herd immunity" in an answer?
The safer route is to describe the mechanism rather than rely on a term: high vaccination coverage reduces the number of susceptible hosts, so chains of transmission are interrupted more often, indirectly protecting people who cannot be vaccinated. "Herd immunity" does not appear anywhere in the 0610 syllabus, and 10.1.12's verb is explain — so the mechanism is the answer either way, and a name on its own is not.
Syllabus reference and sources
Written against: Cambridge IGCSE Biology (0610), syllabus for 2026, 2027 and 2028 (version 2, published December 2025), Subject Content, Topic 10: Diseases and immunity, subtopic 10.1.
Written by: Academiq Edu Instructor Panel
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