Multicellular organisms are those organisms composed of two or more cells, these species include most fungi, animals and plants. On the other hand, unicellular organisms include bacteria and archaea (i.e., prokaryotes), as well as unicellular eukaryotic species (e.g., protists). Multicellular organisms exhibit a higher organizational level compared to unicellular organisms because in these organisms cells are organized into successive hierarchical levels in order to carry out diverse functions (i.e., tissues, organs, organ systems, etc).
