Bacteria are single celled organisms that are prokaryotes. Prokaryotic organisms lack a nucleus and many of the organelles found in other cells. They do still, however, contain genetic information, cytoplasm, ribosomes and a cell membrane. Bacteria belong to the kingdom Monera. Some bacteria move by means of a flagella which is a whip-like tail while other types of bacteria must rely on air, water or other means to move them along. Some bacteria are autotrophs and some are heterotrophs.
Bacteria can sometimes be harmful but do have many important roles in nature as well: