Yeast, commonly used in baking and fermentation, belongs to the group Fungi. Yeast are eukaryotic, single-celled microorganisms. They are classified within the Kingdom Fungi. The most common species used in bread making is *Saccharomyces cerevisiae*. Protista is a diverse kingdom of eukaryotic organisms that are not plants, animals, or fungi (e.g., amoeba, algae). Monera is an outdated kingdom that included prokaryotic organisms (bacteria and archaea). Protozoa is a group of single-celled eukaryotes, now typically classified within the Kingdom Protista.