Smallest microorganisms, reproduce inside host cells.

• A. Bacteria
• B. Viruses
• C. Fungi
• D. Protozoa

Answer: (B)

Viruses are the smallest microorganisms and the only ones that reproduce inside a living host cell. They are not made of cells and consist of genetic material wrapped in a protein coat, so they can’t carry out metabolism or replicate on their own. To multiply, they hijack the host cell’s machinery, making the cell produce new viral particles. That dependence on a host for replication and their tiny size set them apart from other microorganisms.

Bacteria are cellular and can reproduce independently by binary fission, and are larger than viruses. Fungi and protozoa are also cellular, eukaryotic organisms and are generally much larger than viruses, capable of growth and reproduction without needing to inhabit a host cell.