Which term is a microscopic infectious agent capable of replicating only in living cells?

• A. Volume
• B. Virus
• C. Verbal
• D. Virulent

Answer: (B)

Viruses are microscopic infectious agents that can replicate only in living cells. They are typically made of genetic material (DNA or RNA) wrapped in a protein coat, sometimes with a lipid envelope. They cannot carry out metabolism or reproduce on their own, so they must invade a host cell and hijack that cell’s machinery to produce new viral components and assemble them into new viruses. This dependence on living cells for replication is what defines them as viruses—obligate intracellular parasites.

Volume is just a measure of space, not a biological entity. Verbal relates to spoken or written language, not an infectious agent. Virulent describes how severe or harmful a disease is, not what causes it.