10. Diseases and immunity
- Syllabus
- 0610–2026–2027
- Section
- 10
- Level
- —
Exam analysis
Most tested topics
10.1 Diseases and immunity
- Syllabus
- 0610–2026–2027
- Topic
- 10.1
- Level
- —
Define a pathogen
A pathogen is a disease-causing organism.
Pathogens include organisms that enter or live in a host and cause disease.
A pathogen is the disease-causing organism, not the disease, symptom, antibody or host.
Define a transmissible disease
A transmissible disease is a disease in which the pathogen can pass from one host to another.
The defining feature is transfer of the pathogen between hosts, whether transmission is direct or indirect.
Not every disease is transmissible; deficiency, inherited and many non-infectious diseases do not pass between hosts.
Distinguish direct and indirect pathogen transmission
Pathogens reach a new host by direct contact or through an indirect route.
| Route | Required examples |
|---|---|
| direct contact | contact between hosts, including blood and other body fluids |
| indirect | contaminated surfaces, food, animals or air |
The route describes how the pathogen moves; a symptom is not a transmission route.
Describe the body's defences against pathogens
Body defences block pathogen entry or destroy pathogens that enter.
| Defence | Action |
|---|---|
| skin | physical barrier |
| hairs in the nose | trap particles and pathogens |
| mucus | traps pathogens on surfaces |
| stomach acid | kills many swallowed pathogens |
| white blood cells | engulf pathogens or produce antibodies |
Red blood cells transport oxygen; white blood cells provide the cellular defence listed here.
Explain how public-health measures control disease spread
Disease control breaks transmission routes before pathogens reach a new host.
| Measure | How it reduces spread |
|---|---|
| clean water supply | prevents drinking water carrying pathogens |
| hygienic food preparation | prevents contamination and reduces pathogens in food |
| personal hygiene | removes pathogens from hands and limits transfer |
| waste disposal | keeps faeces and other waste away from people, food and water |
| sewage treatment | removes or kills pathogens before water returns to the environment |
The importance is pathogen removal or route interruption; detailed sewage-treatment stages are not required.
Define active immunity
Active immunity is defence against a pathogen produced when the body's own lymphocytes make antibodies.
Because the body mounts the immune response itself, active immunity can also produce memory cells and long-term protection.
Receiving ready-made antibodies is passive immunity, not active immunity.
Describe pathogen antigens
Each pathogen has its own antigens, and those antigens have specific shapes.
Antigens are recognised as foreign features and trigger a specific immune response.
Antigens belong to the pathogen; antibodies are made by lymphocytes in response.
Describe how antibodies defend against pathogens
Antibodies are proteins that bind to antigens on pathogens.
| After binding | Outcome |
|---|---|
| direct action | the pathogen is destroyed or neutralised |
| marking | phagocytes recognise and destroy the marked pathogen |
Antibodies bind antigens; phagocytes perform the engulfing step.
Explain antibody–antigen specificity
A specific antibody has a binding shape complementary to one specific antigen.
Only a matching antibody binds effectively, so antibodies made against one pathogen usually do not protect against a different pathogen.
Complementary means matching fit, not identical shape.
Explain how active immunity is acquired
Active immunity develops after infection by a pathogen or after vaccination.
| Exposure | Immune result |
|---|---|
| infection | pathogen antigens stimulate the body's antibody response |
| vaccination | harmless pathogen material or antigens stimulate the same type of response |
Breast milk and placental antibodies provide passive, not active, immunity.
Outline the process of vaccination
Vaccination exposes the immune system safely to pathogen antigens and establishes memory.
| Stage | Event |
|---|---|
| 1 | weakened pathogens or their antigens enter the body |
| 2 | antigens stimulate lymphocytes |
| 3 | lymphocytes produce specific antibodies |
| 4 | memory cells are produced |
| 5 | later exposure triggers a faster response and long-term protection |
A vaccine supplies antigens, not a permanent store of ready-made antibodies.
Explain how vaccination controls disease spread
Vaccination reduces the number of susceptible hosts, so an infected person is less likely to pass the pathogen to another susceptible person.
When many people are immune, transmission chains are interrupted and unvaccinated or vulnerable people are less likely to encounter the pathogen.
Vaccination lowers transmission risk; it does not guarantee that every vaccinated person can never be infected.
Define passive immunity
Passive immunity is short-term defence provided by antibodies acquired from another individual.
| Source | Transfer |
|---|---|
| mother during pregnancy | antibodies cross the placenta |
| mother after birth | antibodies pass in breast milk |
| medical treatment | ready-made antibodies may be given |
The recipient receives antibodies rather than making them through an immune response.
Explain why breast-feeding supports infant immunity
Breast milk transfers maternal antibodies to an infant, providing passive immunity while the infant's own immune system is still developing.
These ready-made antibodies give immediate, short-term protection against pathogens the mother has antibodies against.
Breast-feeding transfers antibodies, not memory cells, so this protection is passive.
State why passive immunity is temporary
Memory cells are not produced in passive immunity.
The acquired antibodies are gradually broken down and are not replaced by a memory-cell response, so protection is short-term.
Passive immunity can act immediately, but immediate action does not make it long-lasting.
Describe cholera and its transmission
Cholera is a disease caused by a bacterium and transmitted in contaminated water.
Faecal contamination can place the bacterium in water; drinking that contaminated water transfers it to a new host.
The exact learning job is disease cause and water transmission; treatment is a separate issue and is not evidence for this objective.
Explain how cholera causes diarrhoea and dehydration
The cholera bacterium produces a toxin that changes ion and water movement in the small intestine.
| Stage | Consequence |
|---|---|
| toxin acts on intestinal cells | chloride ions are secreted into the small intestine |
| chloride concentration in the lumen rises | lumen water potential decreases |
| water moves from blood/tissues into the gut by osmosis | watery diarrhoea occurs |
| water and ions leave the body | dehydration and loss of ions from blood result |
Water follows the water-potential gradient into the gut; the toxin does not block the intestine.