* Bacteria: These are single-celled prokaryotes (organisms without a nucleus). They are incredibly diverse and can be found in almost every environment on Earth.
* Archaea: These are also single-celled prokaryotes, but they are distinct from bacteria in their biochemistry and genetics. They often live in extreme environments like hot springs or highly saline lakes.
* Eukarya: These are organisms with cells that have a nucleus and other membrane-bound organelles. This domain includes all plants, animals, fungi, and protists.
So, bacteria represent only one of the three domains of life.
The reason why there are three domains is based on the fundamental differences in their evolutionary history, cell structure, and biochemistry. While both bacteria and archaea are prokaryotes, they are as different from each other as they are from eukaryotes.
