A microorganism (often called a microbe)
is a tiny single-cell organism that you need a microscope to see.
Types of microorganism:
(fungi, algae, protozoa)
There are billions of microorganisms inside us
and on our skin. Over 95% of those inside us right now
are helpful - or at least harmless. The rest are
not nice to have around - they may multiply rapidly inside our
bodies and cause infectious illness; these nasty ones are called pathogens.
Pathogens cause us problems by either:
- releasing toxins (poisons), or
- invading and damaging our cells (if they are viruses).
To a microbe, a human being is a bit like a luxury hotel
on legs, so it tries to get inside our bodies. The body has two ways of
first line of defence
is to keep the pathogen
. The body is like a fortress: the outer defences include
our thick skin, sticky mucus and cilia in the respiratory system,
enzymes in tears - and acid in the stomach which kills most pathogens
that enter our stomachs via our food.
The second line of defence kicks
in if a pathogen does manage to get through via the normal openings
or via a cut or graze. What happens is that our white blood
cells attack the microbes in various ways
- and usually manage to destroy them. (In addition, if we have a wound,
a protective scab forms.)
Two ways in which doctors help the body's fight against
Vaccination, in which pathogens
are introduced into the body in a weakened form. This process causes
the body to produce enough white blood cells to protect itself against
the pathogens, while not getting diseased.
Antibiotics, which are effective
against bacteria but viruses. Some strains of bacteria are resistant
» Pathogens: bacteria and
blood cells: part 1 and part
[ This page has been adapted from www.bbc.co.uk/schools/gcsebitesize/science