Unit 1 Biology AS pathogen notes

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Biology and disease Unit 1 summary
Micro organism: a term for a single celled organism that is too small to be seen
without a microscope. (Includes viruses & bacteria) ­ Many of these micro
organisms live in our body and cause us no harm (some are beneficial)
A Pathogen: is a micro organism that causes disease (includes bacteria, viruses
and fungi).
Disease: A description of certain symptoms, either physical or mental, or both.
Disease suggests a malfunction of the body or mind which has an adverse affect
on good health (Mental, physical and social aspects).
For a micro organism to be classed as a pathogen it has to:
Gain entry to the host.
Colonise the tissues of the host. ­ If a pathogen manages to gain entry to the
host and then colonise the tissues, it will cause an infection. (DISEASE ONLY
Resist the defences of the host.
Cause damage to the host tissues.
Transmission: is when a pathogen is transferred from one individual to another.
How micro organisms enter the body
They generally enter the body by penetrating one of the organism's interfaces with
the environment. ­ A surface or boundary linking two systems (external environment
with the internal environment of the body)
Skin: Thick continuous barrier which is usually very effective against
infection/invasion ­ only occurs when the skin is broken.
Some of the interfaces of the body have evolved to allow the exchange of material
between the internal and external environments (thin, moist, large surface area, lots
of blood vessels). This makes it easier for molecules to enter ­ as well as
pathogenic micro organisms!
Therefore interfaces of the body are likely points of entry (and include):
The gas exchange system ­ many do it this way (influenza, TB, bronchitis
pathogens are most likely to enter this way)

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The digestive system ­ food & water may carry pathogens into
stomach/intestines via the mouth (cholera & typhoid)
The body has developed some natural defences to prevent entry of
Mucous layer cover gas exchange surfaces, ­ thick/sticky (hard to penetrate).
Production of enzymes that can break down the pathogens.
Production of stomach acid (kills micro organisms).…read more


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