AQA · GCSE · Biology

    Course version: 8461 · Version from Sept 2018

    Pathogens are microorganisms that cause infectious disease.

    Full specification wording

    Communicable (infectious) diseases: Pathogens are microorganisms that cause infectious disease.

    A pathogen is any microorganism that causes disease when it enters a host.

    Checked against the AQA 8461 specification (opens in a new tab) on .

    • Point 3 of 8
    • 4 key terms

    Study notes

    From the checked teaching notes for this specification point.

    The idea

    A pathogen is any microorganism that causes disease when it enters a host. 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. Recognising a named microorganism as a pathogen therefore requires stating both that it is a microorganism and that it causes disease.

    What earns the marks

    • 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.

    Common mistakes and how to put them right

    • Calling every microorganism a pathogen.

      Put it right by stating that only those causing disease are pathogens.

    • Confusing infectious with inherited or deficiency disease.

      Put it right by linking infectious disease to transmission by a pathogen.

    • Saying a pathogen is a poison rather than an organism.

      Put it right by describing it as a microorganism that causes disease.

    Exam 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.

    Try the lesson

    The start of the Communicable (infectious) diseases: Pathogens are microorganisms that cause infectious disease. lesson, made from checked teaching notes for this specification point.

    Have a go first

    Which of the following statements provides the most accurate definition of a pathogen?

    Listen

    A pathogen is any microorganism that causes disease when it enters a host. 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. Recognising a named microorganism as a pathogen therefore requires stating both that it is a microorganism and that it causes disease. A strong answer earns marks for these 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. A common slip: Calling every microorganism a pathogen. Instead, stating that only those causing disease are pathogens. Exam tip: Use the full phrase microorganism that causes disease in definitions to secure the causation idea.

    See it

    A top-down flowchart. At the top is a box labelled Microorganism, which leads down to a decision box asking Causes disease? From this decision, a branch labelled Yes leads to a box labelled Pathogen, and a branch labelled No leads to a box labelled Harmless or useful microorganism. The Pathogen box leads to a box labelled Causes infectious disease, which leads to a box labelled Can be transmitted between organisms. The Pathogen box also leads to a box labelled Example: bacterium causing tuberculosis. The Harmless or useful microorganism box leads to a box labelled Examples: gut bacteria, decomposers.
    Shows that a pathogen is a microorganism that causes disease, distinguishing it from harmless or useful microorganisms and linking it to infectious disease that can be transmitted.

    Key words

    Say what each word means before you turn the card.

    Pathogen

    Try answering aloud or in your head before turning the card.

    Infectious disease

    Try answering aloud or in your head before turning the card.

    Causation of disease

    Try answering aloud or in your head before turning the card.

    Transmission between hosts

    Try answering aloud or in your head before turning the card.

    See every definition
    Pathogen
    A microorganism that causes disease when it enters a host.
    Infectious disease
    A disease that can be transmitted between organisms, since infectious means the disease can spread between hosts.
    Causation of disease
    The microorganism itself, not a toxin in food or a genetic fault, triggers the illness.
    Transmission between hosts
    The passing of an infectious disease from one organism to another.

    Label the diagram

    Some boxes have lost their names. Pick the right name for each number.

    The diagram again, with 3 boxes numbered instead of named. A top-down flowchart. At the top is a box labelled Microorganism, which leads down to a decision box asking Causes disease? From this decision, a branch labelled Yes leads to a box labelled Pathogen, and a branch labelled No leads to a box labelled Harmless or useful microorganism. The Pathogen box leads to a box labelled Causes infectious disease, which leads to a box labelled Can be transmitted between organisms. The Pathogen box also leads to a box labelled Example: bacterium causing tuberculosis. The Harmless or useful microorganism box leads to a box labelled Examples: gut bacteria, decomposers.

    • 1Box 1

    • 2Box 2

    • 3Box 3

    0 of 3 labelled

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