Scientific classification sorts all life forms on Earth into five kingdoms: monera, protista, fungi, plantae, and animalia. Together they form the tree of life.

Earth is home to a vast variety of living things—organisms of every size and description that live and reproduce in myriad different ways. Scientists divide all these organisms into groups with members that have basic similarities: the broadest divisions are called kingdoms. Currently, life on Earth is divided into five kingdoms: monera, protista, fungi, plantae, and animalia.

Within each kingdom, organisms are further subdivided into smaller and smaller groups: phylum, class, order, family, genus, and species. The species name is specific—it refers to a single organism rather than a group.

Monera

The monera are the simplest of organisms, almost all microscopic. Each individual is just one prokaryotic cell—a cell that has no membrane bound nucleus or organelles; that is, there are no structures inside the cell. Some monera can produce their own food by photosynthesis (using energy from the sun to produce food) like plants do, but many cannot. Some have whip like flagella that allow them to move. Bacteria and blue-green bacteria belong to the monera.

Since the adoption of the five kingdoms, science has determined that some prokaryotes are so different from the rest that the kingdom must be subdivided. These organisms, which evolved along a completely different route, tend to live in extremely harsh environments. They are called archaeobacteria (sometimes spelled archeobacteria). Thus, the kingdom monera may soon be divided into two: archeobacteria and eubacteria, making six kingdoms.

Protista

Like the monera, protista are single-celled organisms; however, the major difference is the organization of the cell. Protista are eukaryotes: a eukaryotic cell has a membrane-bound nucleus and other organelles inside, separate from the rest of the cell contents. Most protista can move. Some produce their own food by photosynthesis; others must ingest other living things. Amoebae, some algae, diatoms and other organisms belong to the protista.

Fungi

Fungi include both single-celled (yeasts) and multicellular (molds, mushrooms etc.) organisms that are generally visible to the naked eye. Some are quite large. Fungal cells have nuclei; however, they don’t move on their own, nor do they make their own food. Most fungi get nutrients from decaying organic material.

Plantae

Plantae includes the plants: living things that don’t move, and that produce their own food through photosynthesis. Plants are multicellular, composed of eukaryotic cells. Plants are generally green, visible to the naked eye, and found in great diversity in many environments on Earth

Animalia

Animals belong to animalia: multicellular (eukaryotic) organisms that move about and must obtain nutrients by consuming other organisms. Kingdom animalia includes familiar organisms such as mammals, birds, and reptiles, but also less typical things like jellyfish.

The Tree of Life

The system for classifying life forms that starts with the kingdoms is often referred to as the “tree of life:” the first life on Earth is the trunk of the tree, which then divides into five branches (the kingdoms), which go on dividing into continually smaller branches and twigs. A species lies at the tip of each twig. The Tree of Life Web Project, an interesting and educational website uses this analogy to provide information about life on Earth.

Sources:

Five Kingdom Classification System. Caprette, David R. Rice University: Experimental Biosciences.

Unlocking the Mysteries. Kingdoms. Utah Education Network.