* Protista: This kingdom includes single-celled eukaryotes like amoebas, paramecia, and algae. They are too small to be seen with the naked eye.
* Monera: This kingdom is now often divided into the domains Bacteria and Archaea, but still includes microscopic single-celled prokaryotes.
While the other kingdoms can have microscopic members, they also include many macroscopic organisms:
* Fungi: While molds and yeasts are microscopic, mushrooms and some other fungi are large enough to be seen without a microscope.
* Plantae: Many plants, like trees and flowers, are macroscopic. However, microscopic algae and other plants are also part of this kingdom.
* Animalia: Most animals, like mammals, reptiles, and birds, are macroscopic. However, microscopic invertebrates like mites and nematodes exist as well.
Therefore, Protista and Monera (Bacteria and Archaea) are the only kingdoms whose members are *always* microscopic and require viewing under a microscope.
