But in the last few decades the most interesting concepts in taxonomy have been happening at the highest levels. For years, some biologists were frustrated by microorganisms that had characteristics of both animals and plants. They urged putting these organisms into a separate kingdom. They don't respond to stimuli like animals, but they lack chlorophyll and most of the structures of green plants. Some biologists began treating fungi as a separate kingdom.
Bacteria differ from all other organisms.
If fungi deserve a kingdom, so do bacteria. Fungi Bacteria Domains and Superkingdoms Bacteria differ from all other organisms in not having a cell nucleus. Their DNA floats freely within the cell. The difference between bacteria and everything else suggests we need something even higher than the kingdom. Maybe an empire, but most biologists prefer the term Domains.