Communicable (infectious) diseases — AQA GCSE Biology
Test yourself on Communicable (infectious) diseases with AQA GCSE practice questions.
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Communicable (infectious) diseases explained
A pathogen is any microorganism that causes disease when it enters a host.
Read the full explanation
The key idea is causation: the microorganism itself, not a toxin in food or a genetic fault, triggers the illness, and the disease can pass from one organism to another. Many microorganisms are harmless or useful, such as gut bacteria and decomposers, so pathogen is a functional label rather than a whole group. For example, the bacterium that causes tuberculosis is a pathogen, whereas the bacteria making yoghurt are not. Students should link the term to transmission, since infectious means the disease can spread between hosts. Recognising a named microorganism as a pathogen therefore requires stating both that it is a microorganism and that it causes disease.
Your focus
- State that a pathogen is a microorganism causing infectious disease.
- Give a named example of a pathogen and the disease it causes.
- Distinguish pathogens from harmless microorganisms in a given list.
Communicable (infectious) diseases exam tips
Marking Points
- Defines a pathogen as a microorganism that causes disease.
- States that the disease caused is infectious, meaning it can be transmitted between organisms.
- Distinguishes pathogens from harmless or beneficial microorganisms such as decomposers and gut bacteria.
- Links a named example, such as the bacterium causing tuberculosis or a virus causing influenza, to disease causation.
- Uses the term correctly when describing how a disease spreads from host to host.
Examiner Tips
- 💡Use the full phrase microorganism that causes disease in definitions to secure the causation idea.
- 💡When naming an example, state the disease as well as the pathogen so the link is explicit.
- 💡Check whether a question asks for a definition or an example, and answer the precise command word.
Common Mistakes
- Calling every microorganism a pathogen; correct by stating that only those causing disease are pathogens.
- Confusing infectious with inherited or deficiency disease; correct by linking infectious disease to transmission by a pathogen.
- Saying a pathogen is a poison rather than an organism; correct by describing it as a microorganism that causes disease.