What is the defining characteristic of organisms in Kingdom Monera?

The defining characteristic of organisms in Kingdom Monera is that they are prokaryotic organisms. They lack a defined nucleus and other membrane-bound organelles and are typically unicellular. Monera includes bacteria and archaea, which are two of the most ancient groups of organisms on Earth. Monera is distinct from organisms in other kingdoms, such as Protista, Fungi, Plantae, and Animalia, which are all eukaryotic organisms with a true nucleus and other membrane-bound organelles.