What is bacteria? Are bacteria the only prokaryotic organisms?

Bacteria are single-celled, prokaryotic microorganisms that lack a nucleus and membrane-bound organelles. They play essential roles in ecosystems and human health. No, bacteria are not the only prokaryotic organisms. Archaea are also prokaryotic organisms, and although they share many similarities with bacteria, they are distinct in their genetic and biochemical properties, and they often live in extreme environments.