Prokaryotic cells are single cells that evolved before eukaryotes, which are organisms whose cells contain nuclei and organelles. A prokaryotic cell has no true nucleus or membrane-bound structures called organelles. Prokaryotic cells are usually bacterial species.
Prokaryotic cells are small and range in length from 2 to 5 micrometers. Some prokaryotes live in hostile environments on the ocean floor or in areas devoid of oxygen. Prokaryotes living in these types of environments have adapted to using different types of compounds for energy. Prokaryotic cells reproduce through binary fission, in which a cell grows and divides, and the two resulting daughter cells are exactly alike.
Although prokaryotic cells do not have nuclei or organelles, they have certain structures adapted to their way of life. A cell wall gives these cells shape and strengthens them. Their genetic material is circular in shape and lies in a region of the cell called the nucleoid. Some prokaryotes also contain plasmids, smaller circles of genetic material that can be transferred from one organism to another.