Pathogens and how disease spreads
Communicable diseases are caused by pathogens: microorganisms that can pass from one person, animal or plant to another. You need to know the four types, how they spread, and a named example of each.
Part 1 of 3: Learn it
In short
- The four pathogens are bacteria, viruses, fungi and protists.
- They spread through the air, in water, by direct contact or through a vector such as a mosquito.
- Hygiene, isolation, killing vectors and vaccination reduce the spread.
Where this is in your specification
Spec points: AQA 4.3.1.1 to 4.3.1.5 (Combined Trilogy 4.3.1.1 to 4.3.1.5), Edexcel Topic 5, OCR B5.1
| Board | Topic: Infection and response |
|---|---|
| AQA 8461 | 4.3 (8461); 4.3 (8464) |
| Edexcel 1BI0 | Topic 5 |
| OCR J247 | B5 |
| Eduqas C400 | 3.1 to 3.3 |
| Cambridge IGCSE 0610 | 10.1, 15.1 |
| National 5 C807 75 | Multicellular organisms: 6 Transport systems in animals (blood and pathogens) |
How pathogens make us ill
- Bacteria reproduce rapidly in the body and may release toxins that damage tissues.
- Viruses live and reproduce inside cells, and the cells burst as new viruses are released.
- Fungi and protists can damage tissues and cells directly.
Named diseases
| Disease | Pathogen | Spread | Notes |
|---|---|---|---|
| Measles | virus | droplets from coughs and sneezes | fever and a red rash; prevented by vaccination |
| HIV | virus | sexual contact and exchange of body fluids | attacks immune cells; controlled by antiretroviral drugs |
| Tobacco mosaic virus | virus (plants) | contact between plants | mottled leaves; less photosynthesis |
| Salmonella | bacterium | undercooked food or poor food hygiene | fever, cramps, vomiting; UK poultry are vaccinated |
| Gonorrhoea | bacterium | sexual contact | thick discharge; treated with antibiotics, prevented by condoms |
| Rose black spot | fungus | spores carried by water and wind | black spots on leaves; treated with fungicides |
| Malaria | protist | mosquitoes (a vector) | repeated fevers; prevented by nets and stopping mosquitoes breeding |
Reducing the spread
- Hygiene: hand washing, disinfecting surfaces, cooking food properly.
- Isolating infected people, animals or plants.
- Destroying or controlling vectors, such as draining standing water where mosquitoes breed.
- Vaccination, so fewer people can catch and pass on the disease.
Name the four types of pathogen.
Show the answer
Bacteria, viruses, fungi and protists.
Part 2 of 3: See it worked
Worked examples
Example 1
A bacterium divides every 20 minutes. Starting with one bacterium, how many will there be after 3 hours, if none die?
- 3 hours = 180 minutes, and 180 ÷ 20 = 9 divisions
- The number doubles each time: 2⁹
- 2⁹ = 512
Answer: 512 bacteria.
Example 2
Explain how putting up nets over beds reduces the number of cases of malaria.
- Malaria is caused by a protist carried by mosquitoes
- Nets stop mosquitoes biting people while they sleep
- So the protist is not passed into the blood
Answer: Fewer bites by the vector means fewer people are infected with the protist.
Common mistakes
- Saying antibiotics treat viral diseases such as measles. Antibiotics only work on bacteria.
- Calling the mosquito the pathogen. It is the vector; the protist is the pathogen.
- Mixing up rose black spot (a fungus) and tobacco mosaic virus.
- Saying all bacteria cause disease. Only some are pathogens.
How is rose black spot spread?
Show the answer
Its spores are carried by water and wind.
Part 3 of 3: Test yourself
Check yourself
Answer each one in your head or on paper first, then open it to check.
Name the four types of pathogen.
Bacteria, viruses, fungi and protists.
How is rose black spot spread?
Its spores are carried by water and wind.
Why do viruses damage the cells they infect?
They reproduce inside the cells, which burst when the new viruses are released.
Jobs that use this
Each link opens the job profile on the National Careers Service (England). In the rest of the UK: My World of Work (Scotland), Careers Wales, nidirect careers (Northern Ireland).
Full lessons and marked practice for this course are coming soon to Brainlag Learn. See courses