The largest and broadest category in the biological classification system is the kingdom
. Monera, Protista, and Fungi compose three of the five kingdoms; the other two are Plantae, and Animalia.
The kingdom Monera includes bacteria and the cyanobacteria (often referred to as "blue-green algae"). These one-celled organisms are prokaryotic. Prokaryotic organisms have neither nucleus nor organelles in their cytoplasm, possess only a single chromosome, have small ribosomes, and reproduce by simple fission. Many of the organisms (called autotrophic) can synthesize their own foods, and some (called heterotrophic) digest preformed organic matter.
The second kingdom, Protista, includes the protozoa, the one-celled algae, and the slime molds. The cells of these organisms are eukaryotic. They are unicellular, and they may be autotrophic or heterotrophic. Eukaryotic organisms have a nucleus and organelles in their cytoplasm, possess multiple chromosomes, have large ribosomes, and reproduce by mitosis.
The third kingdom, Fungi, includes the yeasts, molds, mildews, mushrooms, and other similar organisms. The cells of this kingdom are eukaryotic and heterotrophic. Some fungal species are unicellular, whereas other species form long chains of cells and are called filamentous fungi. A cell wall containing chitin or cellulose is found in most members. Food is taken in by the absorption of small molecules from the outside environment.
Now that you have insight into these three kingdoms, you'll probably want to look up the complicated words used to describe the way they live, grow, and make more of their kind. Grab a dictionary and dig into the diversity of life!