Which statement correctly describes protozoa?

Protozoa are primarily characterized by their single-celled structure, which is a defining feature of these microorganisms. While some protozoa may form colonies, they are fundamentally unicellular organisms that can carry out all necessary life processes within a single cell. This allows them to thrive in a variety of environments, including soil, freshwater, and marine ecosystems, often exhibiting diverse forms and behaviors.

The ability of protozoa to exist as individual cells or in colony-like groupings allows for complex interactions within their respective environments. However, they do not require extreme environments to survive; this trait is more characteristic of certain bacteria and archaea. Additionally, while protozoa can exhibit some complexity in their life cycles and structural adaptations, they are primarily unicellular and should not be considered multicellular, nor are they characterized by complex structural forms like higher organisms.