Cambridge IGCSE Biology 0610: Diseases and immunity – Study Guide

This study guide teaches topic 10, Diseases and immunity, of the Cambridge IGCSE Biology 0610 syllabus for examination in 2026, 2027 and 2028. The topic has one section, 10.1 Diseases and immunity. Its Core statements (pathogens, transmission, body defences and controlling the spread of disease) are examined on Papers 1 and 3. Most of the immunity content, and all of the cholera content, is Supplement: it is marked Extended only below and is examined on Papers 2 and 4.

Course pages: Cambridge IGCSE Biology hub and the printable 0610 checklist. After this guide, use the revision notes and then the practice questions. White blood cells were introduced in topic 9: see the transport in animals study guide.

What this unit covers

10.1 statement	What you must be able to do	Tier
1–2	Describe a pathogen and a transmissible disease	Core
3	State direct and indirect ways pathogens are transmitted	Core
4	Describe the body defences: skin, hairs in the nose, mucus, stomach acid, white blood cells	Core
5	Explain how five public-health measures control the spread of disease	Core
6–10	Active immunity; antigens and antibodies; complementary shapes; how active immunity is gained	Extended only
11–12	Outline vaccination; explain its role in controlling spread	Extended only
13–15	Passive immunity; breast-feeding; no memory cells in passive immunity	Extended only
16–17	Cholera: cause, transmission and how the toxin causes diarrhoea	Extended only

Pathogens and transmissible diseases (Core)

A pathogen is a disease-causing organism. Bacteria and viruses are the usual examples.

A transmissible disease is a disease in which the pathogen can be passed from one host to another. The host is the organism the pathogen lives in.

How pathogens are transmitted

• Direct contact, including through blood and other body fluids. Examples: sharing needles; touching an infected wound.
• Indirectly, including from contaminated surfaces, food, animals and air. Examples: a door handle touched by an infected person; undercooked meat; droplets breathed out by someone with a respiratory infection.

When a question asks you to “state” a method, name the route and give a brief example.

Body defences (Core)

The syllabus limits you to five defences. Learn what each one does.

Defence	How it protects you
Skin	A physical barrier that stops pathogens entering the body
Hairs in the nose	Trap dust and pathogens in the air you breathe in
Mucus	Sticky; traps pathogens in the airways
Stomach acid	Hydrochloric acid kills pathogens in food and drink
White blood cells	Phagocytosis (engulfing pathogens) and antibody production

The first four are barriers or chemical defences. They act before pathogens reach the blood. White blood cells deal with pathogens that do get in.

Controlling the spread of disease (Core)

You must be able to explain why each measure matters. The explanation should always name the transmission route it blocks.

• A clean water supply. Pathogens in water are removed or killed before people drink it, so waterborne diseases are not passed on.
• Hygienic food preparation. Washing hands, keeping raw and cooked food apart, cooking food thoroughly and storing it cold stop pathogens reaching or growing in food.
• Good personal hygiene. Washing hands after using the toilet and before eating removes pathogens picked up from surfaces, so they are not carried to the mouth or to other people.
• Waste disposal. Rubbish attracts animals such as flies and rats, which can carry pathogens. Collecting and disposing of waste safely removes breeding sites and food for them.
• Sewage treatment. Human faeces can contain pathogens. Treating sewage stops them getting into drinking water or onto food crops. You do not need the stages of treatment.

Worked example: interpreting data on clean water

A town recorded 450 cases of a waterborne disease in the year before a new water-treatment plant opened, and 36 cases in the year after.

(a) Calculate the percentage decrease in cases.

decrease = 450 − 36 = 414
percentage decrease = 414 ÷ 450 × 100 = 92%

(b) Suggest why some cases still occurred. Some people may still drink untreated water from other sources, or the pathogen may be passed on by other routes, such as contaminated food or poor personal hygiene.

The key skill is dividing by the starting value (450). In part (b), “suggest” means give a sensible reason based on transmission routes; there is no single correct answer.

Active immunity (Extended only)

Active immunity is defence against a pathogen by antibody production in the body. Your own lymphocytes make the antibodies.

Antigens and antibodies

• Each pathogen has its own antigens. These are molecules, usually on its surface, with specific shapes.
• Antibodies are proteins made by lymphocytes. They bind to antigens.
• Specific antibodies have complementary shapes which fit specific antigens. An antibody made against one pathogen will not bind to a different one.
• Binding leads either to the direct destruction of pathogens, or to marking pathogens for destruction by phagocytes.

Gaining active immunity

Active immunity is gained in two ways:

1. After an infection by a pathogen: you catch the disease, your lymphocytes respond, and you recover.
2. By vaccination: your lymphocytes respond without you having the disease.

Either way, memory cells are produced. If the same pathogen enters again, memory cells make antibodies much faster and in greater quantity, so the pathogen is destroyed before you become ill. This is long-term immunity.

Vaccination (Extended only)

The syllabus asks you to outline the process in three steps. Learn them in order.

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

The role of vaccination in controlling spread

When a large proportion of a population is vaccinated, most people are immune. A pathogen that enters the population finds few people it can infect, so it is passed on less often. The number of cases falls, and people who cannot be vaccinated (for example, very young babies) are also less likely to meet the pathogen. This is often called herd immunity. Where vaccination rates fall, the disease can spread again.

Passive immunity (Extended only)

Passive immunity is a short-term defence against a pathogen by antibodies acquired from another individual. Your own lymphocytes do not make them.

Two natural examples in the syllabus:

• across the placenta, from mother to fetus before birth
• in breast milk, from mother to baby after birth

Memory cells are not produced in passive immunity. The antibodies are gradually broken down, so the protection does not last.

Why breast-feeding matters

A newborn baby’s immune system is not yet fully developed. Breast milk contains the mother’s antibodies against pathogens she has met. These give the baby passive immunity while its own immune system develops, which protects it during the first months of life.

Active vs passive: side by side

Feature	Active immunity	Passive immunity
Source of antibodies	Made by own lymphocytes	From another individual
How gained	Infection or vaccination	Placenta or breast milk
Memory cells	Produced	Not produced
Duration	Long-term	Short-term

Cholera (Extended only)

Cholera is a disease caused by a bacterium. It is transmitted in contaminated water, typically water containing sewage from infected people.

How cholera causes its symptoms, as a chain of causes:

1. The cholera bacterium produces a toxin.
2. The toxin causes secretion of chloride ions into the small intestine.
3. This lowers the water potential in the gut, so water moves by osmosis from the blood and tissues into the gut.
4. The result is diarrhoea, dehydration and loss of ions from the blood.

Link this to the Core content: clean water and sewage treatment are exactly the measures that prevent cholera spreading.

Worked example: explaining a symptom

Explain why a person with cholera may feel weak and thirsty even though they are drinking water. Water drawn into the gut by osmosis is lost in diarrhoea faster than it can be replaced, so the person becomes dehydrated. Ions are lost from the blood at the same time. Each step in the chain earns credit, so write them in order: toxin, chloride ions, osmosis, diarrhoea, dehydration and ion loss.

Common errors

• Calling a pathogen “a disease”. It is the organism that causes the disease.
• Saying mucus “kills” pathogens. It traps them; stomach acid is the defence that kills.
• Saying antibodies “eat” pathogens. Phagocytes engulf pathogens; antibodies bind to antigens.
• Writing that antibodies and antigens have the “same shape”. The shapes are complementary.
• Saying a vaccine contains antibodies. It contains weakened pathogens or their antigens; antibodies are what your body makes in response.
• Saying passive immunity is long-term, or that it produces memory cells.
• In cholera answers, saying the toxin “causes water loss” without the chloride ion and osmosis steps.
• Explaining clean water, hygiene or waste disposal without naming how the pathogen would otherwise be passed on.

Next steps

• Condense this into the diseases and immunity revision notes.
• Test yourself with the diseases and immunity practice questions.
• Take the free 0610 Core diagnostic or 0610 Extended diagnostic.

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.