Prokaryotic Cells
Prokaryotes are single-celled organisms that are the earliest and most primitive forms of life on earth. As organized in the Three Domain System, prokaryotes include bacteria and archaeans. Some prokaryotes, such as cyanobacteria, are photosynthetic organisms and are capable of photosynthesis. Many prokaryotes are extremophiles and are able to live and thrive in various types of extreme environments including hydrothermal vents, hot springs, swamps, wetlands, and the guts of humans and animals (Helicobacter pylori).