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What is disease?

  • Certain symptoms caused by disease, either physical or mental.
  • Malfunction of the body or mind which has an affect on good health.
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Microorganisms as pathogens

  • Gain entry to the host 
  • Colonise the tissues of the host 
  • Resist the defences of the host cell
  • Cause damge to the host 

Pathogens include: Viruses, bacteria and fungi.

  • If pathogens colonise a tissue it causes an infection
  • A disease is caused when the infection leads to recognisable symptoms
  • When the pathogen is trasferred from one individual to another is called transmission
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Entering the body

  • They get into the body by penetrating the organisms interfaces with the environment 
  • An example of an interface is the skin, which forms a thick, continuous layer which acts as a barrier to infection
  • The gas exchange system is also an interface, it has developed a mucus layer which is hard to penetrate 
  • The digestive system allows food and water, which may contain pathogens, to be consumed. 
  • The body produces enzymes to breakdown the pathogens and also produces stomach acid to kill microorganisms
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Causing disease

  • Damaging host tissues: the large number of pathogens can cause the surrounding tissues to not function properly, inhibit the synthesis of DNA or breakdown the membrane of the cells.
  • Produce toxins: produce toxins which are harmful to the surrounding tissues.
  • Pathogens, lifestyle and genetic factors can all cause disease.
  • The faster a pathogen divides, the faster it can cause disease. 
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