What feature is characteristic of a multicellular organism but not of a single-cell organism?

In multicellular organisms, the formation of specialized functions is a defining characteristic that arises from the differentiation of cells. Each cell in a multicellular organism can develop into a specific type that performs unique tasks, contributing to the overall functioning of the organism. For example, in human beings, we have muscle cells responsible for movement, nerve cells for signaling, and epithelial cells for protection and absorption. This specialization allows multicellular organisms to operate more efficiently and adapt to complex environments.

In contrast, a single-celled organism, such as bacteria or yeast, carries out all necessary life functions within one cell. These organisms do not have the capacity to develop specialized cells since they consist of just a single cell. Therefore, the lack of specialization in single-celled organisms differentiates them fundamentally from multicellular ones where specialization is key to their complexity and organization. This feature highlights the complexity and advanced functionality that multicellular systems can achieve compared to solitary organisms.