Prokaryote, pronounced proh KAR ee oht, also called moneran (pronounced muh NIHR uhn), is the name of a group of primitive one-celled organisms. Prokaryotes make up the kingdom Prokaryotae. This kingdom consists of blue-green algae, also called cyanobacteria, and bacteria. Prokaryotes live alone or in clusters called colonies. The individual organisms can be seen only with a microscope, but some colonies are visible with the unaided eye. Prokaryotae is one of the five kingdoms of living things recognized by most scientists. The other kingdoms are Animalia (animals), Fungi (fungi), Plantae (plants), and Protista (protists). Some scientists classify prokaryotes as part of either the protist or plant kingdom.

Most biologists believe prokaryotes are among the oldest types of organisms. Unlike all other living cells, prokaryotes do not have a nucleus surrounded by a membrane. But they do have a nuclear area that contains DNA, the substance that controls heredity. Prokaryotes also lack typical organelles, structures that perform functions in other cells.

Prokaryotes live throughout the world, even where no other life can survive. For example, blue-green algae live in the water of hot springs as well as in frozen wastelands. Free-living bacteria dwell throughout the soil and water, and parasitic species live within nearly all multicelled plants and animals.