Which of the following is a single-celled microorganism that possesses characteristics of both plants and animals?

The correct answer is protozoa, which are single-celled microorganisms that display characteristics of both plants and animals. Protozoa can be considered animal-like because they are often motile and can ingest food, behaving similarly to animals in their feeding habits. They can also be found in aquatic environments and in soil.

While bacteria are also single-celled microorganisms, they lack a true nucleus and other organelles found in more complex cells. Bacteria are classified as prokaryotes, which fundamentally differentiate them from protozoa. Viruses, on the other hand, are not considered living organisms because they cannot reproduce independently and require a host cell to replicate. Fungi are a separate kingdom of organisms that can be multicellular or single-celled, but they do not share the dual characteristics of plants and animals in the same way that protozoa do. Thus, protozoa represent the category that encapsulates both plant-like and animal-like traits.