A type of organism classified as a prokaryote includes bacteria and archaea. Prokaryotes are characterized by their simple cell structure, lacking a defined nucleus and membrane-bound organelles. This group of organisms is incredibly diverse and can adapt to various environments. Prokaryotes play essential roles in ecosystems, such as decomposers and producers, and are crucial for processes like nitrogen fixation. Their metabolic versatility enables them to survive in extreme conditions, making them key players in ecological balance and biogeochemical cycles.