Multicellular organisms are organisms that consist of more than one cell, in contrast to unicellular organisms.
All species of animals, land plants and most fungi are multicellular, as are many algae, whereas a few organisms are partially uni- and partially multicellular, like slime molds and social amoebae.
The body has levels of organization that build on each other. Cells make up tissues, tissues make up organs, and organs make up organ systems. The function of an organ system depends on the integrated activity of its organs. For instance, digestive system organs cooperate to process food.