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Defending against infection
Pathogens are microorganisms such as bacteria and viruses
that cause disease. Bacteria release toxins, and viruses damage
our cells. White blood cells can ingest and destroy pathogens.
They can produce antibodies to destroy pathogens, and
antitoxins to neutralise toxins.
In vaccination pathogens are introduced into the body…

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and plants. Singular is bacterium. ]. They are among the smallest
organisms known and consist of a fragment of genetic material inside a
protective protein coat.
Viruses can only reproduce inside host cells, and they damage the
cell when they do this. A virus can get inside a cell and,…

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White blood cells can:
ingest pathogens and destroy them
produce antibodies to destroy pathogens

produce antitoxins that neutralise the toxins released by pathogens
In a written examination, it is easy to get carried away and waffle on
about things such as invaders and battles, but stick to the point. Note…

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a protein that has a chemical 'fit' to a certain antigen. When a
lymphocyte with the appropriate antibody meets the antigen, the
lymphocyte reproduces quickly, and makes many copies of the
antibody that neutralises the pathogen.
Antibodies neutralise pathogens in a number of ways:
they bind to pathogens and damage…

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Vaccines in early childhood can give protection against many serious
diseases. Sometimes more than one vaccine is given at a time, like the
MMR triple vaccine against mumps, measles and rubella.
Sometimes vaccine boosters are needed, because the immune
response 'memory' weakens over time. Antitetanus injections may
need to be…

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Since the discovery of penicillin, many other antibiotics have been
discovered or developed. Most antibiotics used in medicine have been
altered chemically to make them more effective and safer for humans.

Resistance
Bacterial strains can develop resistance to antibiotics. This happens
because of natural selection. In a large population of…

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