How do viruses differ from bacteria in terms of cellularity and replication?

• A. Viruses are acellular and require a host cell to replicate; bacteria are single-celled organisms capable of independent replication.
• B. Viruses are multicellular and replicate independently; bacteria are acellular and require host cells.
• C. Viruses are single-celled organisms that replicate independently; bacteria are acellular and require a host.
• D. Viruses and bacteria are both acellular and replicate independently.

Answer: (A)

Viruses differ from bacteria in that they are acellular particles that lack their own cellular machinery. They can’t carry out energy production or protein synthesis on their own, so they must invade a living cell and hijack that cell’s machinery to replicate their genome and assemble new virus particles. Bacteria, by contrast, are cellular organisms—single cells with their own metabolism and ribosomes—that can grow, divide, and reproduce independently under suitable conditions. So the key distinction is that viruses are acellular and rely on a host cell to replicate, while bacteria are single-celled organisms capable of independent replication.