Bacteria are single celled organisms. They are prokaryotes, meaning that they are simple cells that do not contain organelles. They differ from other kingdom classifications in that they are single celled (unlike plants, animals, and fungi), and they cannot grow their own food (unlike protists, the other single celled kingdom). Bacteria are found literally almost everywhere on earth, including land, water, air, and even extreme places such as volcanic craters, ice caverns in Antarctica, and the darkness of the deepest ocean floors. Bacteria have many beneficial uses in society including the production of food and drink through fermentation and the breakdown of sewage and food in septic tanks. Beneficial bacteria are found in the human body, particularly the intestinal tract. Here, they help the body break down biochemicals to be absorbed by the body.