Scientists classify living things to make it easier to study and understand the behaviors, lives and evolutionary progression of millions of life forms. They use a system known as taxonomy to classify living things into kingdoms, phyla, classes, orders, families, genera and species according to their characteristics.
Scientists first classify a life form into one of five kingdoms: Animalia, Plantae, Fungi, Protista or Monera. Organisms found in kingdom Animalia are multicellular beings capable of movement via muscular organs, cilia or flagella. They get their nutrients by absorption. Animal cells possess nuclei and other organelles, but they do not feature cell walls or chloroplasts.
Organisms in the kingdom Plantae are also multicellular, but do not typically move, with the exception of some of their gametes moving via flagella or cilia. They obtain nutrients through photosynthesis, which requires sunlight, and their cells possess nuclei, other organelles, cell walls and chloroplasts.
Living things in the kingdom Fungi are also multicellular. Their cells have nuclei, organelles and cell walls, like plant cells, but they lack chloroplasts. Like animals, they acquire nutrients via absorption.
Kingdom Protista features single-celled organisms that obtain nutrients through consuming other organisms or photosynthesis; in some cases, they utilize both methods. Eubacteria and archeobacteria are members of kingdom Monera. They are single-celled, lack a nucleus and organelles and are bound by a cell wall.