Edexcel GCSE Combined Science: Biology

Revision Notes

5.1.2 Pathogens

Types of Pathogen

  • Communicable diseases are spread by pathogens
  • A pathogen is any microorganism that causes disease in another organism (e.g. in plants or animals)
  • Many microorganisms are pathogens including:
    • Bacteria
    • Fungi
    • Protists (protoctists)
    • Viruses
  • Not all species within these groups (apart from the viruses) are pathogens, as many bacteria, fungi and protists are harmless and do not cause disease
  • However, all viruses are pathogenic as they can only exist by living inside the living cells of other organisms (or by using these cells to create more viruses)

Pathogenic bacteria

  • Pathogenic bacteria do not always infect the hosts of cells, they can remain within body cavities or spaces
  • Toxins produced by the bacteria also damage cells
  • They are small and can reproduce very quickly
  • Bacterial infections include:
    • M. tuberculosis causes tuberculosis (TB) in humans
    • N. meningitidis causes bacterial meningitis in humans
    • Helicobacter Pylori causes stomach ulcers
    • V. Cholerae causes cholera in humans

Pathogenic fungi

  • Fungal diseases are much more common in plants than animals
  • Fungi can be single-celled or multicellular (with threads of hyphae)
  • The spores they produce allow them to infect other organisms
  • In plants, fungal diseases tend to be much more serious and can threaten entire crops
  • Fungal diseases include:
    • Cattle ringworm and athletes foot are fungal diseases in animals
    • Black Sigatoka is a fungal disease in bananas
    • Chalara Ash Dieback is a fungal disease that affects ash trees

Pathogenic protists

  • Protists are a diverse group of eukaryotic (and usually unicellular) organisms
  • They are parasites which means they need a host in order to survive
  • Only a small number of protists are pathogenic, but the diseases they cause are often serious
  • Examples of diseases caused by protists are:
    • Plasmodium falciparum is a protist that causes severe forms of malaria in humans
    • P. infestans causes the infamous potato blight

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Ruth graduated from Sheffield University with a degree in Biology and went on to teach Science in London whilst also completing an MA in innovation in Education. With 10 years of teaching experience across the 3 key science disciplines, Ruth decided to set up a tutoring business to support students in her local area. Ruth has worked with several exam boards and loves to use her experience to produce educational materials which make the mark schemes accessible to all students.
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