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Since the first antibiotic was discovered in 1928, many more have been developed
and used to treat bacterial infections. Some bacteria have mutated and become
resistant to antibiotics, but new drugs are constantly being developed and tested.

Antibiotics are substances that kill bacteria or prevent their growth. They do…

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Drug testing
Drugs and their origins
Drugs are substances that cause changes to the body. Some can help the body, others
can harm it.

Certain drugs can be extracted from natural sources and their existence has been
recognised for a long time. For example, willow bark was used by the…

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Salmonella bacterium cell

Bacteria come in many shapes and sizes, but even the largest are only ten micrometres
long (ten-millionths of a metre).
Bacteria are living cells and can multiply rapidly in favourable conditions. Once inside the
body, they release poisons or toxins that can make us feel ill.


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chemicals in tears
chemicals in sweat
stomach acid

The skin

Cross-section of skin

The skin covers the whole body and protects it from physical damage, microbe infection
and dehydration. It is difficult for microbes to penetrate the skin's dry, dead outer cells.
In addition the sebaceous glands produce oils which…

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A white blood cell ingesting disease-causing bacteria

In a written examination, it is easy to get carried away and write about things like
invaders and battles. You should stick to the point. Note that:
The pathogens are not the disease, they cause the disease.
White blood cells do not eat…

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Vaccination involves putting a small amount of an inactive form of a pathogen into the
body. Vaccines can contain:

live pathogens treated to make them harmless
harmless fragments of the pathogen
toxins produced by pathogens
dead pathogens
These all act as antigens. When injected into the body, they stimulate white…

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Hepatitis C virus. DNA are enclosed in a protein coat.
Some common diseases like influenza (flu) and the common cold are caused by
viruses. These mutate quickly, and this changes their surface proteins. This makes
it almost impossible to develop a permanent vaccine against them. A new flu
vaccine has…

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the only disease that has been eradicated from the planet by vaccination. This was
possible because smallpox is spread by direct contact, and not through the air.
This made it possible to vaccinate enough people in the world to completely stop the
disease from spreading.

Some other diseases are more…


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