1.2 Bacteria e.g. E.coli, vibro
1.3 Fungi e.g. candida albicans,
2 A disease is a description of certain symptoms.
2.1 Disease suggests a malfunction of
body and mind which has an adverse
effect of good health.
2.1.1 Disease has mental, physical and social aspects.
3 To consider a microorganism as a pathogen it must be able to
3.1 1) gain entry to the host
3.2 2) colonise the tissues of the host
3.3 3) resist the defences of the host
3.4 4) cause damage to the host
4 Once a pathogen has entered a host and colonises its
tissues, an infection occurs.
4.1 If this infection leads to
recognisable symptoms, a
4.2 When a pathogen is transferred from
one individual to another, transmission
5 Pathogens cause disease by
5.1 Producing toxins
5.1.1 e.g. the cholera bacterium produces
toxins which lead to excessive water loss
from the lining of the intestines.
5.2 Damaging host tissues
5.2.1 rupturing them to release nutrients
5.2.2 breaking down nutrients inside the cell for
their own use, starving and eventually
killing the cell
5.2.3 replicating inside the cell
causing it to burst
6 Microorganisms can enter into the body and cause disease through the
6.1 Gas-exchange system as when breathing in, not all of them are trapped by the
mucus lining the lung epithelium. The pathogens that are trapped in the mucus
are moved up the trachea, towards thee mouth where they are removed by the
beating cilia. The pathogens which are not trapped reach the alveoli where they
invade cells and cause damage.
6.2 The skin, when damaged, allows pathogens to enter the bloodstream.
Although the blood clots and dries to form a scab, preventing the entry of
pathogens, some get in before the scab forms.
6.3 The digestive system allows pathogens to enter in the form
of food or drink. Most are killed by the acidic conditions of the
stomach but some survive and pass into the intestines where
they invade the gut wall and cause damage.