Final answer:
Scenedesmus is considered a simple colony because its cells are similar, with minimal specialization and coordination. It represents an intermediate stage of organization between unicellular and complex multicellular life forms.
Step-by-step explanation:
Scenedesmus is considered a simple colony because it is an aggregation of cells that are relatively undifferentiated and function almost identically to one another. Unlike organisms with complex multicellularity, which exhibit a high degree of cell specialization and organization into distinct tissues, Scenedesmus cells maintain a level of autonomy similar to unicellular organisms, while being united for collective function. A simple colony like Scenedesmus is a step between solitary cellular life forms and highly integrated multicellular organisms. Their coordination is minimal, and specialized structures are not present or are very basic, such as the cytoplasmic bridges seen in the colonial chlorophyte Volvox. Therefore, the morphology of Scenedesmus cells, when observed microscopically, would show little differentiation, indicative of a simple tissue.