Which description best fits bacteria?

• A. Viruses that require host cells
• B. Prions
• C. Living organisms that move
• D. Living microorganisms that reproduce, have a cell wall, and are able to move

Answer: (D)

Bacteria are living microorganisms characterized by being single-celled prokaryotes with cell walls, and they reproduce to multiply. They often move using structures like flagella, though not all do. This combination—being living microorganisms, having a cell wall, and the ability to reproduce and move—captures the defining traits of bacteria.

Viruses are not living in the same sense and require host cells to reproduce, so a description that emphasizes needing a host cell doesn’t fit bacteria. Prions are misfolded proteins, not cells, so they don’t fit the idea of living microorganisms. A description that only says “living organisms that move” is too vague, since movement isn’t universal to all bacteria and it omits the cell wall and reproductive aspect.