What type of algae consists of single-celled or small colonies that are suspended in water?

Planktonic algae are characterized by their existence as single-celled organisms or small colonies that float freely in the water column. These algae are often microscopic and are crucial components of aquatic ecosystems, forming the base of the food web for many aquatic organisms. They derive their name from "plankton," which refers to organisms that are unable to swim against the current.

This group includes various species of phytoplankton, which are essential for photosynthesis in aquatic environments. Planktonic algae play a significant role in oxygen production and the overall health of aquatic ecosystems, influencing water quality and supporting a wide range of aquatic life.

While filamentous algae can form long, thread-like structures, and macrophytic algae refer to larger, often multicellular varieties that can be rooted or floating, these do not fit the description of being single-celled or existing in small colonies suspended in water. Colonial algae, on the other hand, exist as groups but typically can be visualized as larger aggregates, which differs from the microscopic nature of planktonic algae.