Which statement best describes filamentous algae?

The statement that best describes filamentous algae is that the cells are attached end to end. Filamentous algae are typically composed of long, thin chains or filaments of cells that can appear thread-like in structure. This arrangement is a key characteristic of filamentous algae, distinguishing them from other types of algae that may be unicellular or have different structural formations.

Other options, while describing certain characteristics of organisms, do not accurately represent filamentous algae. For instance, single-celled organisms refer to organisms that exist as individual cells, which does not capture the filamentous form. Branching structures may indicate a more complex growth form that is not typical for filamentous algae, as they primarily grow in straight or lightly branched filaments. Lastly, the lack of chlorophyll does not apply because filamentous algae contain chlorophyll, allowing them to perform photosynthesis and contribute to aquatic ecosystems. Thus, the correct description emphasizes the unique structure of filamentous algae, characterized by their end-to-end cellular arrangement.