Final answer:
Multicellular organisms have the advantage of forming complex organ systems due to cell specialization and organization into tissues, organs, and organ systems.
Step-by-step explanation:
The advantage of multicellular organisms is that they can form complex organ systems. This ability arises from the specialization of cells, which allows the cells to perform specific functions more efficiently. Specialization leads to the formation of tissues, and these tissues are organized to form organs. In turn, organs are grouped into organ systems, which perform a variety of functions necessary for the survival of the organism. This organizational structure is far more complex and advantageous in multicellular organisms compared to unicellular organisms, where all life processes occur within a single cell.