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This topic takes on average 120 minutes to read.

Topic last updated: 09 Nov 2023
    • Biology Biology
    • Ico Science Science
    • 14-16
    • 120

Health, disease and the development of medicines

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Communicable disease

Communicable diseases are cause by pathogens, which are infectious. Pathogens include bacteria, fungi, protozoa and viruses, and they are transmitted between people or animals to allow the disease to be spread. This transmission can occur via direct contact, by water or by air.


  • Prokaryotic cells
  • Reproduce rapidly inside the body
  • Very small when compared to your cells
  • May produce toxins (poisons) inside the body
  • May damage your cells
Bacteria KS4


  • Viruses are not cells – they are a combination of genetic material and protein
  • Smaller than bacteria
  • Reproduce rapidly inside the body, specifically inside your cells
  • They invade the cells and use the replication machinery to reproduce. This causes the cell to burst, destroying the host cell
Viral infection

When the body is infected with a communicable disease, it fights back via the immune system to fight off the infection. Modern medicine has also developed many successful treatments to assist the body’s natural defences, including antibiotics.

You can find more detailed information about pathogens in the pathogens resource, and more information on specific infectious diseases that they can cause in the diseases resource.