Which option correctly identifies a non-living infectious agent that can replicate only inside living cells?

• A. Bacteria
• B. Virus
• C. Fungi
• D. Prion

Answer: (B)

Viruses are non-living infectious agents that can replicate only inside living cells. They lack cellular structure and their own metabolism, so they can’t multiply on their own. To reproduce, a virus must invade a host cell and hijack its machinery—enzymes, ribosomes, and nucleotides—to produce viral components and assemble new particles. Outside a host, viruses exist as inert particles and do not grow or metabolize. This dependence on a living cell for replication is what sets them apart from living microbes like bacteria and fungi. Prions are infectious proteins without genetic material; they spread by prompting normal proteins to misfold, and they don’t replicate via cellular machinery the way viruses do. So, the virus is the correct identification.