Under which of the following conditions will viruses grow?

• A. Agar plate
• B. Artificial nutrient media
• C. Cell culture
• D. Glass culture plates

Answer: (C)

Viruses can only multiply inside living cells because they lack their own metabolic machinery. They don’t carry out energy production or protein synthesis on their own, so there’s nothing for them to use in a nutrient broth or on an inert surface. An agar plate or a glass culture plate is just a solid surface, not a living environment for viral replication. Artificial nutrient media provide nutrients for cells to live, but without actual host cells there’s nothing for the virus to infect or hijack. In cell culture, you have living cells in a controlled environment that the virus can infect; once inside, the virus uses the cell’s machinery to produce new virus particles, leading to replication. That’s why cell culture is the condition under which viruses grow.