The protists are basically a miscellaneous category, with no defining characteristic. Some are autotrophs, some heterotrophs, and some are decomposers. They can be single celled or multi celled. Examples are slime molds, algae, protozoa, and ameobas. Also called prokayota, this kingdom includes bacteria and all prokaryotes.
Prokaryotes are organisms with cells that have no nucleus or membrane-enclosed organelles.
Monera is the only kingdom which includes prokaryotes, so that is the determining factor for inclusion in this kingdom. Most are single-celled organisms. In terms of number of species and places where they live, bacteria are the most diverse group of organisms. A new system of classification at the kingdom level has recently been gaining favor. This new system is more phylogenetically correct, meaning it is a more accurate representation of how life evolved.