BO VEISLAND, MI&I / SCIENCE PHOTO LIBRARY BO VEISLAND, MI&I / SCIENCE PHOTO LIBRARY
Intestinal bacteria. Artwork of bacteria (light- coloured spheres and rods) in the large intestine (colon). Bacteria living in the colon break down food that the body cannot otherwise digest. Intestinal bacteria are an important source of vitamin K. The number of bacteria living in the colon is immense. Humans typically excrete in their faeces every day over 100 billion bacteria of more than 75 species; it is estimated that bacterial debris makes up about one third of the weight of faeces.
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