Cambridge IGCSE Biology 0610: Diseases and immunity – Revision Notes

For full explanations and a worked data example, use the diseases and immunity study guide. These notes condense topic 10 (section 10.1, statements 1–17) of the Cambridge IGCSE Biology 0610 syllabus for examination in 2026, 2027 and 2028. Statements 1–5 are Core (Papers 1 and 3). Statements 6–17 are Supplement, marked Extended only (Papers 2 and 4).

Links: Cambridge IGCSE Biology hub, printable checklist, practice questions for this topic, 0610 Core diagnostic and 0610 Extended diagnostic. Blood cells are covered in the transport in animals revision notes.

Definitions

Term	Definition to learn	Tier
Pathogen	A disease-causing organism	Core
Transmissible disease	A disease in which the pathogen can be passed from one host to another	Core
Active immunity	Defence against a pathogen by antibody production in the body	Extended only
Antigen	Molecule on a pathogen with a specific shape; each pathogen has its own	Extended only
Antibody	Protein that binds to an antigen; has a complementary shape to a specific antigen	Extended only
Passive immunity	Short-term defence by antibodies acquired from another individual	Extended only

Transmission (Core)

Route	Includes	Example
Direct contact	Blood and other body fluids	Shared needles; contact with an infected wound
Indirect	Contaminated surfaces, food, animals, air	Door handles; undercooked food; flies; droplets in air

Body defences (Core)

The syllabus list is exactly five:

• Skin – physical barrier.
• Hairs in the nose – trap particles and pathogens.
• Mucus – traps pathogens in the airways.
• Stomach acid – kills pathogens in food and drink.
• White blood cells – phagocytosis and antibody production.

Controlling spread (Core)

Measure	Why it controls spread
Clean water supply	Pathogens removed or killed before water is drunk
Hygienic food preparation	Stops pathogens reaching food or growing in it
Good personal hygiene	Handwashing removes pathogens before they reach the mouth or other people
Waste disposal	Removes food and breeding sites for animals that carry pathogens
Sewage treatment	Stops pathogens in faeces reaching water or crops (no stage details needed)

Method in steps: explaining a control measure

A Core “explain” question on controlling spread usually needs two linked points per measure. Use this pattern:

1. Name the action (for example, boiling or treating water; washing hands before handling food).
2. Say what it does to the pathogen (kills it, removes it, or stops it reaching food, water or people).
3. Link it to transmission (so the pathogen is not passed from one host to another).

Example for waste disposal: rubbish is collected and buried or burned → flies and rats have less food and fewer breeding sites → fewer animals carry pathogens onto food and surfaces.

Worked reminder: percentage change in cases

Subtract the new number of cases from the old, divide by the old number, and multiply by 100. For example, cases falling from 250 to 40 is a decrease of 210, and 210 ÷ 250 × 100 = 84%. Give the answer to the precision the question asks for.

Antibodies at work (Extended only)

Method in steps: from antigen to destruction

1. Pathogen enters; its antigens have a specific shape.
2. Lymphocytes produce antibodies with a complementary shape.
3. Antibodies bind to the antigens.
4. Either the pathogen is destroyed directly, or it is marked for destruction by phagocytes.
5. Memory cells remain, giving long-term immunity (active immunity only).

Active immunity is gained after an infection or by vaccination.

Vaccination (Extended only)

Method in steps: the outline the syllabus wants

1. Weakened pathogens or their antigens are put into the body.
2. Antigens stimulate an immune response by lymphocytes, which produce antibodies.
3. Memory cells are produced, giving long-term immunity.

Role in controlling spread: if most of a population is vaccinated, a pathogen finds few people it can infect, so it is passed on less and cases fall. Unvaccinated people are also protected because they are less likely to meet the pathogen.

Worked reminder: a second exposure

After a first vaccine dose, antibody concentration rises slowly and peaks at a low level. After a second dose (or a later infection), memory cells respond, so antibodies are made faster and reach a much higher concentration. On a graph, look for a shorter delay and a taller peak for the second response.

Passive immunity (Extended only)

• Antibodies come from another individual: across the placenta and in breast milk.
• Short-term, because the antibodies are broken down and no memory cells are produced.
• Breast-feeding matters because it gives an infant antibodies (passive immunity) while its own immune system is still developing.

Cholera (Extended only)

Chain of causes — learn every link:

cholera bacterium (from contaminated water)
  → produces a toxin
  → chloride ions secreted into small intestine
  → water moves into gut by osmosis
  → diarrhoea, dehydration, loss of ions from the blood

Linking the Extended content back to Core

Cholera is a good example of why the Core measures matter. The bacterium is transmitted in contaminated water, so a clean water supply and sewage treatment break its route between hosts. Good personal hygiene and hygienic food preparation stop it passing on from hands or food. If a question gives you a cholera outbreak, use the Core measures for “how could the spread be reduced” and the toxin chain for “how does it make people ill”.

Where white blood cells fit (Extended only)

• Phagocytes engulf pathogens by phagocytosis. They also destroy pathogens that antibodies have marked.
• Lymphocytes produce antibodies and, in active immunity, memory cells.
• Both are white blood cells, which are one of the five Core body defences.

Must-know distinctions

Pair	Difference
Pathogen vs disease	The organism vs the illness it causes
Direct vs indirect transmission	Contact with the host (including body fluids) vs via surfaces, food, animals or air
Antigen vs antibody (Extended only)	On the pathogen vs made by lymphocytes
Active vs passive immunity (Extended only)	Own antibodies, memory cells, long-term vs another’s antibodies, no memory cells, short-term
Vaccine vs antibody (Extended only)	Vaccine contains weakened pathogens or antigens; it does not contain antibodies
Lymphocyte vs phagocyte (Extended only)	Produces antibodies vs engulfs pathogens

Command words in this topic

Command word	What to write
State	A short answer with no reason, e.g. “across the placenta”
Describe	The main points or features, e.g. how each body defence works
Explain	What happens and why, e.g. clean water removes pathogens so they are not swallowed
Outline	The key steps only, briefly (used for vaccination)
Compare	A point about both things in the same sentence, e.g. active is long-term whereas passive is short-term
Suggest	A sensible reason applied to a new context, e.g. why some cases still occur after water treatment

Quick self-test

1. Define a pathogen.
2. State two indirect ways a pathogen can be transmitted.
3. How does stomach acid protect the body?
4. Name two body defences that trap pathogens.
5. Explain why sewage treatment helps control the spread of disease.
6. Cases of a food-borne infection at a school fell from 250 to 40 after new kitchen hygiene rules. Calculate the percentage decrease.
7. (Extended) State what is meant by active immunity.
8. (Extended) Why does an antibody against one pathogen not bind to a different pathogen?
9. (Extended) State the two ways active immunity can be gained.
10. (Extended) Give two ways a baby gains passive immunity.
11. (Extended) Why is passive immunity short-term?
12. (Extended) Explain how the cholera toxin causes dehydration.

Answers

1. A disease-causing organism.
2. Any two of: contaminated surfaces, food, animals, air.
3. The acid kills pathogens in food and drink.
4. Hairs in the nose; mucus.
5. It stops pathogens in human faeces getting into drinking water or onto food, so they are not passed to new hosts.
6. (250 − 40) ÷ 250 × 100 = 84%.
7. Defence against a pathogen by antibody production in the body.
8. Each pathogen has antigens with a specific shape; the antibody’s shape is complementary only to the antigen it was made against.
9. After infection by the pathogen; by vaccination.
10. Across the placenta; in breast milk.
11. No memory cells are produced, and the acquired antibodies are broken down.
12. The toxin causes chloride ions to be secreted into the small intestine; water moves into the gut by osmosis; water is lost in diarrhoea.

Where marks are usually lost

• Defining a pathogen as “a germ” or “a disease” instead of a disease-causing organism.
• Adding defences that are not on the syllabus list and leaving out ones that are.
• Saying mucus kills pathogens; it traps them.
• Explaining a public-health measure without naming the transmission route it blocks.
• Writing “same shape” instead of complementary shape for antibodies and antigens.
• Stating that vaccines contain antibodies, or leaving out memory cells from the vaccination outline.
• Claiming passive immunity produces memory cells or lasts for years.
• Skipping the chloride ion step or the word osmosis in the cholera explanation.
• In percentage-change calculations, dividing by the final value instead of the starting value.

Official syllabus

Cambridge IGCSE Biology 0610 syllabus for examination in 2026, 2027 and 2028 (Version 3), section 10 Diseases and immunity. Published by Cambridge University Press & Assessment.