AQA Biology AS unit 1: chapter 1

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pathogens = microorganisms that cause disease (include bacteria, viruses and fungi)

For a microorganism to be classed as a pathogen it must:

  • gain entry to the host
  • colonise the tissues of a host
  • resist the defences of a host
  • cause damage to the hosts tissues

This leads to infection. Disease occurs when infection leads to recognisable symptoms. When a pathogen is transferred from one individual to another it is known as transmission.

for a pathogen to cause disease it must affect the body by damaging the hosts tissues and producing toxins.

Microorganisms get into the body by penetrating one of the organisms interfaces with the enviroment. (for example the skin)

Interfaces (such as the gas exchange surface and the digestive surface) allow the


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