Final answer:
Unicellular organisms carry out life functions within a single cell that can have complex internal organization, whereas multicellular organisms divide these functions among specialized cells, tissues, and organs. Multiplicity of cells in multicellular organisms allows for a more efficient and specialized execution of life's processes.
Step-by-step explanation:
Both unicellular and multicellular organisms are capable of carrying out all the necessary functions of life, though they do so in different ways. Unicellular organisms are single-celled and manage all life processes within that one cell, showcasing a remarkable degree of internal complexity and organization. On the other hand, multicellular organisms perform life processes through a division of labor, with specialized cells, tissues, organs, and organ systems each performing distinct roles.
In unicellular organisms, even though they are comprised of only one cell, there can be sophisticated internal structures that perform functions analogous to organs in multicellular organisms. For instance, the Euglena possesses organelles that carry out complex functions similar to an eye or kidney in higher organisms, despite being single-celled. However, these individual cells are not considered multicellular.
Multicellular organisms differ as they consist of many cells that often vary in shape and function, organized into complex structures. Through a developmental process, these organisms dictate the type of cells that are produced, where they are produced, and how they are organized into tissues and organs. This complex organization allows multicellular organisms to execute life processes with greater efficiency and specialization than unicellular organisms.