Which term is defined as a tiny, nonliving particle that requires a host cell to reproduce?

• A. Bacteria
• B. Virus
• C. Protozoa
• D. Fungus

Answer: (B)

That description points to a virus. A virus is a tiny, nonliving particle that cannot carry out metabolism or reproduce on its own. It carries genetic material inside a protein coat (and sometimes a lipid envelope) and must enter a host cell to hijack that cell’s machinery—ribosomes, enzymes, and energy sources—to replicate its genome and synthesize viral proteins. Only after the host cell’s systems are co-opted do new virus particles assemble and exit, often harming or killing the cell. In contrast, bacteria, protozoa, and fungi are living cellular organisms with their own metabolism and the ability to reproduce independently, so they don’t fit the description of a nonliving particle that needs a host to reproduce.