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Controlling Infectious Disease
· The micro organisms that cause infectious disease are
called pathogens. The two main types of pathogens are
known as bacteria and viruses.…read more

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Bacteria
· Very small cells which
can reproduce rapidly
inside your body.
· They make you feel ill by
damaging your cells and
producing toxins
(poisons).
· But...some bacteria are
useful if they're in the
right place; e.g. the
digestive system.…read more

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Viruses
· These are not cells. They're
tiny and usually no more
than a coat of protein around
some genetic material.
· They replicate themselves by
invading your cells and using
the cells' machinery to
produce copies of
themselves. The cell will
usually the burst, releasing
all the new viruses.
· The cell damage is what
makes you feel ill.…read more

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Defence System
1. Your skin, plus hairs and mucus in your respiratory tract
stop a lot of nasties getting inside your body.
2. And to try and prevent micro organisms getting into the
body through cuts, small fragments of cells (called
platelets) help blood clot quickly to seal wounds. If the
blood contains low numbers of platelets then it will clot
more slowly.
3. But if something makes it through, your immune system
kicks in. The most important part of your immune
system is the white blood cells. They travel around in
your blood and crawl into every part of you, constantly
patrolling for microbes. Whey the come across an
invading microbe they have three lines of attack.…read more

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Role of white blood cells How it protects you against disease.
Ingesting micro organisms White blood cells can engulf foreign cells and digest them.
Producing antibodies Every invading cell has unique molecules (antigens) on its
surface. When your white blood cells come across a foreign
antigen (i.e. one it doesn't recognise), they will start to
produce proteins called antibodies to lock on to and kill the
invading cells. The antibodies are specific to that type of
antigen ­ they won't lock on to any others. Antibodies are
then produced rapidly and flow all round the body to kill
all similar bacteria or viruses. If the person is infected with
the same pathogen again the white blood cells will rapidly
produce the antibodies and kill it ­ the person is naturally
immune to that pathogen and won't get ill.
Producing antitoxins The white blood cells produce antitoxins which counteract
the toxins released by the pathogens.…read more

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