Cell type

Animals have evolved a greater diversity of cell types in a multicellular body (100–150 different cell types), compared with 10–20 in plants, fungi, and protists. The exact number of cell types is, however, undefined, and the Cell Ontology, as of 2021, lists over 2,300 different cell types.

Multicellular organisms

Nearly all multicellular organisms contain cells specialised for different functions. Most distinct cell types arise from a single totipotent cell that differentiates into hundreds of different cell types during the course of development. Differentiation of cells is driven by different environmental cues (such as cell–cell interaction) and intrinsic differences (such as those caused by the uneven distribution of molecules during division).

Animals and many other sexually reproducing organisms are composed of cells that fall into two fundamental types: germ cells and somatic cells. During animal development, somatic cells become more specialized and form the three primary germ layers: ectoderm, mesoderm, and endoderm. After formation of the three germ layers, cells continue to differentiate until they reach a terminally differentiated state that is much more resistant to changes in cell type than its progenitors.

The simplest organism considered to have well defined cell types are some volvoceans, such as Volvox carteri, in which each organism is composed of distinct and interdependent cell populations, some somatic and some reproductive.