Final answer:
The term for an organism consisting of more than one cell type is 'multicellular'. Multicellular organisms have specialized cells organized into tissues, organs, and organ systems, with complex multicellularity involving cellular differentiation and development.
Step-by-step explanation:
The term used to describe an organism that consists of more than one cell type is multicellular. Multicellular organisms are characterized by having specialized cells that are grouped together to perform specialized functions. These organisms exhibit organization at several levels, including tissues, organs, and organ systems. Moreover, the development of multicellular organisms requires not just a variety of cell types, but also a complex arrangement of these cells into structures that work together to maintain life.
Complex multicellularity implies a sophisticated organization where different cell types form tissues, and tissues come together to form organs, which in turn make up organ systems. All the cells within a multicellular organism typically have the same genetic material, yet through cellular differentiation and developmental processes, they take on diverse forms and functions. This specialization allows multicellular organisms to carry out complex tasks and survive in various environments.
Among the diversity of life on Earth, organisms may also be unicellular, consisting of a single cell, or exhibit simple multicellularity where multiple similar cells may not form distinct tissues or organs. Understanding multicellularity is essential for comprehending the complexities of life forms ranging from fungi and plants to animals and humans.