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AQA GCSE Biology

Pathogens and communicable disease — AQA GCSE Biology revision

Free revision notes, key terms, common exam traps and 5 practice questions with answers. About 5 minutes to read.

Types of pathogen

  • Bacteria reproduce quickly and can release toxins.
  • Viruses reproduce inside cells and burst them.
  • Fungi and protists also cause disease (e.g. rose black spot, malaria).

Defence and treatment

  • Non-specific defences: skin, mucus, cilia, stomach acid.
  • White blood cells: engulf pathogens, make antibodies, make antitoxins.
  • Vaccines contain dead or inactive pathogen so white blood cells make antibodies ready for next time.
  • Antibiotics kill bacteria only — they do not work on viruses.

Key terms

Pathogen
A microorganism that causes disease.
Antibody
Protein made by white blood cells that binds a specific pathogen.
Herd immunity
When enough people are vaccinated that the disease can't spread easily.
Antibiotic resistance
When bacteria evolve so an antibiotic no longer kills them.
Vector
An organism that transfers a pathogen between hosts without being infected itself, e.g. mosquitoes.
Vaccination
Introducing a dead/inactive form of a pathogen to trigger immunity without causing disease.

Common exam traps

  • Saying antibiotics kill viruses.
  • Saying vaccines 'give you immunity instantly' without mentioning antibody production.
  • Confusing antibody (made by you) with antigen (on the pathogen).

Practice questions with answers

  1. 1. Why don't antibiotics treat flu?

    • • Flu is caused by a virus
    • • Flu is not infectious
    • • Antibiotics only work in the stomach
    • • Flu bacteria are resistant

    Answer: Flu is caused by a virus

    Antibiotics target bacterial processes only.

  2. 2. Describe how a vaccine protects a person.

    Answer: It introduces dead or inactive pathogen; white blood cells make antibodies, and memory cells respond faster if the real pathogen appears.

    Three points: inactive pathogen, antibodies, faster secondary response.

  3. 3. Name the vector that spreads malaria.

    Answer: The mosquito.

    Malaria is caused by a protist carried by mosquitoes.

  4. 4. Which is a non-specific human defence?

    • • Antibodies
    • • Stomach acid
    • • Antitoxins
    • • Memory cells

    Answer: Stomach acid

    It kills pathogens in swallowed food regardless of type.

  5. 5. Which type of pathogen causes malaria?

    • • Bacterium
    • • Virus
    • • Protist
    • • Fungus

    Answer: Protist

    Malaria is caused by a protist spread by mosquito vectors.

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