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  • Created on: 07-04-15 12:48

Biology - Infection and Disease 11.4

Bacteria, Fungi and Viruses are the three types of micro-organisms that cause disease. They reproduce rapidly because: 

  • humans are warm (37 degrees C)
  • humans are moist
  • humans have sugars on the surface of our cells


Pathogens are microorganisms that cause infectious disease. Bacteria and viruses are the main pathogens. It enters the body through gaps in the skin. 

 Bacteria and Viruses

Bacteria are microscopic single-celled organisms. They come in many shapes and sizes, but even the largest are only 10 micrometres long - 10 millionths of a metre. Bacteria are living cells and, in favourable conditions, can multiply rapidly. Once inside the body, they release poisons or toxins that make us feel ill. Diseases caused by bacteria include:

  • food poisoning
  • cholera
  • typhoid
  • whooping cough
  • gonorrhoea - a sexually transmitted disease 

Viruses are many times smaller than bacteria. They are among the smallest organisms known and consist of a fragment of genetic material inside a protective protein coat. Viruses can only


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