Bacteria are a single celled microscopic form of life. Frequently they are a parasitical organism without any cell nucleus or other cell organelles. There are a wide variety of bacteria which play a large role in such processes as decay, nitrogen fixation, and fermentation. There are also a wide range of human diseases caused by bacteria.
Bacteria are extremely small organisms which reproduce asexually and occupy almost every known habitat on Earth. Bacteria exist everywhere, living in radioactive waste, soil, water, and in all forms of organic material. They live in the bodies of other creatures, and in fact there are more bacteria in the human body than there are body cells. Whilst most pathogenic bacteria are dealt with by the natural immune system there are diseases which affect the human, directly caused by bacterial infection. –