Causes of Disease Unit 1.1

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Causes of Disease

Learning Objectives:

  • What are pathogens?
  • How do pathogens enter the body?
  • How do pathogens cause disease?


Pathogens are microorganisms (general term for a single-celled organisms that is too small to see without the use of a microscope)  that cause disease. Disease is not a single thing but rather a description of certain symptoms, either physical or mental (or both). Disease suggests a malfunction of body or mind which has an adverse effect on good health. 

For a microorganism to be considered a pathogen it must:

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

Pathogens include bacteria, viruses and fungi. If a pathogen gets into the host and colonises its tissue an infection results. Disease occurs when an infection leads to recognisable symptoms in the host. When a pathogen is transferred from one individual to another it is known as transmission. 

A microorganism normally gets into the body by penetrating one of the organisms' interfaces (a surface or boundary linking…




great thanks :D good luck for tomoz ( if ure exam is then too :L) x



thanks! yep it was, seemed to go pretty well but fingers crossed! x

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