A prokaryote is a type of cell that does not have any nucleus or membrane-bound organelles. Examples of prokaryotes are bacteria and Archaea. Archaea, as their name suggests, are the more primitive of the two. They are extremophiles, meaning they thrive in conditions that would quickly kill most other organisms. The other group, the Eubacteria, are more familiar. Eubacteria include the disease-causing agents and the bacteria in the human body that break down food, among other things.
Prokaryotes are one of two main types of cells. The other type of cell is a eukaryote.
Cell division is performed in prokaryotes by binary fission. As no chromosomes are formed, it is similar to eukaryotic division, with the exception that DNA replication leads directly to cytokinesis (splitting of cell membrane), with no agglomeration into chromosomes first.
Prokaryotes are the most primitive forms of life, so they are immensely important in evolution. Also, though they are far less complex than eukaryotic organisms like dinoflagellates and paramecia, they are still some of the most common life forms. They are continuing to evolve now, developing resistance to antibiotic drugs and rendering them useless.
Impact on Society
Bacteria, despite their small size and simple nature, have an immense impact on human society. Negatively, they have caused epidemics and pandemics, like cholera outbreaks seen in Europe up until the early 20th century, and in less developed countries in modern times. In more recent years, humans have helped to make drug-resistant strains of bacteria. Humans have brought about these stronger bacteria by using only a small amount of antibiotics, for related or unrelated purposes. This small exposure enables the bacteria to develop resistance or even immunity to larger amounts of the drug.
However, bacteria have also impacted society in a positive way. The first artificial life created was a bacterium. Also, bacteria are being studied to determine what may have been the origin of life on Earth, as well as for extraterrestrial life - they are the most likely candidates for this. Outside of science, bacteria are used in industry to create many familiar products, and some plants have nitrogen-fixing bacteria.