What was the old classification term used for all bacteria?

The term "Monera" was historically used to classify all prokaryotic organisms, which include bacteria. In the traditional five-kingdom classification system proposed by Robert Whittaker in 1969, Monera encompassed all bacteria, distinguishing them from other groups of organisms based on their cellular structure. Bacteria, as prokaryotes, lack a defined nucleus and membrane-bound organelles, which set them apart from eukaryotic organisms like protists, fungi, plants, and animals.

The term "Monera" is no longer widely used in modern classification, especially as scientific understanding of the diversity within prokaryotes has advanced. More recent classifications recognize Archaea and Bacteria as separate domains due to significant differences in their genetic, biochemical, and ecological characteristics. This shift illustrates the importance of continuously refining biological classifications as new information becomes available.

In contrast, "Bacteria" refers specifically to one domain within the current classification systems, while "Protozoan" relates to a varied group of eukaryotic microorganisms that are not bacteria, and "Fungi" refers to another distinct kingdom of eukaryotic organisms characterized by their cell walls and mode of obtaining nutrients. Thus, Monera was the comprehensive