The microbes commonly known as ________ are single-celled eukaryotes that are generally motile.

• A. protozoa
• B. archaea
• C. viruses
• D. bacteria

Answer: (A)

Verified step by step guidance

1. Understand the key characteristics described in the question: single-celled, eukaryotic, and generally motile organisms.
2. Recall that eukaryotes have membrane-bound organelles and a defined nucleus, distinguishing them from prokaryotes like bacteria and archaea.
3. Recognize that viruses are not cells at all; they are acellular and require a host to replicate, so they do not fit the description.
4. Identify that protozoa are single-celled eukaryotes known for their motility, often using structures like cilia, flagella, or pseudopodia.
5. Conclude that the correct term to fill in the blank is 'protozoa' based on these characteristics.