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· A disease causing organism
· For a microorganism to be considered a
pathogen it must:
1) Gain entry to the host
2) Colonise tissues of the host
3) Resist defences of the host
4) Cause damage to host tissues
· Include bacteria, viruses and fungi.…read more

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Key terms
· Infection - When a pathogen gains entry and
colonises tissue.
· Disease - recognisable symptoms of the
· Transmission - Spreading of the pathogen
· Interface - surface or boundary linking two
systems.…read more

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How Do Microorganisms get in?
1. Skin:
* thick, continuous layer.
* effective barrier.
* invasion occurs when skin is broken
2. Exchange sites:
* Gas-exchange
* Digestive system
- body linings at exchange systems are thin,
moist, sticky, have a large surface area and well
equipped with blood vessels.…read more

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Natural Defences Of the body
· Mucous layer covering exchange surfaces,
forming a sticky thick barrier- difficult to
· Production of Enzymes to break down
· Production of stomach acid to kill
microorganisms.…read more

Slide 6

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How Pathogens Cause Disease:
· Damaging host tissues:
- sheer number can prevent tissues functioning
- Viruses inhibit synthesis of DNA, RNA and proteins.
- Pathogens may break down membranes of host cells.
· Producing toxins:
-Bacterial pathogens
· Time taken to cause damage depends on how rapidly
pathogen divides.…read more

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