10.1 Diseases and immunity
- Syllabus
- 0610–2026–2027
- Topic
- 10.1
- Level
- —
Learning objectives
10.1.1Pathogen as a disease-causing organism• Describe a pathogen as a disease-causing organism10.1.2Transmissible disease as a disease• Describe a transmissible disease as a disease in which the pathogen can be passed from one host to another10.1.3Pathogen is transmitted: (a) by direct• State that a pathogen is transmitted: (a) by direct contact, including through blood and other body fluids (b) indirectly, including from contaminated surfaces, food, animals and air10.1.4Body defences• Describe the body defences, limited to: skin, hairs in the nose, mucus, stomach acid and white blood cells10.1.5Controlling disease spread• Explain the importance of the following in controlling the spread of disease: (a) a clean water supply (b) hygienic food preparation (c) good personal hygiene (d) waste disposal (e) sewage treatment (details of the stages of sewage treatment are not required)10.1.6Active immunity as defence against• Describe active immunity as defence against a pathogen by antibody production in the body10.1.7Each pathogen has its own antigens• State that each pathogen has its own antigens, which have specific shapes10.1.8Antibodies as proteins that bind• Describe antibodies as proteins that bind to antigens leading to direct destruction of pathogens or marking of pathogens for destruction by phagocytes10.1.9Specific antibodies have complementary• State that specific antibodies have complementary shapes which fit specific antigens10.1.10Active immunity is gained after• Explain that active immunity is gained after an infection by a pathogen or by vaccination10.1.11Process of vaccination: (a) weakened• Outline the process of vaccination: (a) weakened pathogens or their antigens are put into the body (b) the antigens stimulate an immune response by lymphocytes which produce antibodies (c) memory cells are produced that give long-term immunity10.1.12Role of vaccination in controlling• Explain the role of vaccination in controlling the spread of diseases10.1.13Passive immunity is a short-term• Explain that passive immunity is a short-term defence against a pathogen by antibodies acquired from another individual, including across the placenta and in breast milk10.1.14Importance of breast-feeding• Explain the importance of breast-feeding for the development of passive immunity in infants10.1.15Memory cells are not produced• State that memory cells are not produced in passive immunity10.1.16Cholera as a disease caused• Describe cholera as a disease caused by a bacterium which is transmitted in contaminated water10.1.17Cholera bacterium produces a toxin• Explain that the cholera bacterium produces a toxin that causes secretion of chloride ions into the small intestine, causing osmotic movement of water into the gut, causing diarrhoea, dehydration and loss of ions from the blood
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.