A pathogen is microorganism that causes infectious disease. Bacteria and viruses are the main pathogens.
Bacteria are organisms consisting of a single living cell. They come in many shapes and sizes, but even the largest are only 10 micrometres long (10 millionths of a metre). In favourable conditions, they can multiply rapidly. Some bacteria are friendly and help the body to function and stay healthy. Others are harmful and, once inside the body, release toxins (i.e. poisons) that make us feel ill and sometimes kill us. Diseases caused by bacteria include: |
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| A cross-section
of a typical bacterium |
| • food poisoning • typhoid |
• typhoid • whooping cough |
• gonorrhoea (a sexually transmitted disease) |
[ This page has been adapted from www.bbc.co.uk/schools/gcsebitesize/science
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