What describes the mechanism of viruses?

• A. They replicate independently without a host cell.
• B. They require a host cell to survive and replicate, attaches to a healthy cell, takes over cell's machinery, reproduces, and destroys the cell.
• C. They are bacteria that secrete toxins.
• D. They are fungi that invade tissues.

Answer: (B)

Viruses cannot replicate on their own; they must infect a living cell and hijack its machinery to reproduce. They first attach to a susceptible healthy cell, then enter or inject their genetic material. Inside, they repurpose the cell’s ribosomes, enzymes, and energy to manufacture viral components, assemble new viral particles, and then release them—often at the expense of the host cell, which can be damaged or destroyed in the process. This dependence on a host and the takeover of cellular functions distinguishes viruses from bacteria or fungi, which can grow and cause harm through independent replication or other mechanisms.