Which statement about viruses is true?

• A. They are larger than bacteria and can replicate on their own.
• B. They are much smaller than bacteria and must invade a living host cell to replicate.
• C. They contain only DNA, no RNA.
• D. They are the primary cause of fermentation in foods.

Answer: (B)

Viruses are obligate intracellular parasites: they cannot replicate unless they invade a living host cell and use that cell’s machinery to produce new virus particles. They are much smaller than bacteria, typically too small to see without an electron microscope. Their genomes can be either DNA or RNA, but never both, and they lack the cellular machinery for metabolism on their own. Because of this, they don’t carry out fermentation or other metabolic processes by themselves; fermentation in foods is carried out by living microbes like yeast and bacteria. So the true statement is that viruses are much smaller than bacteria and must invade a living host cell to replicate.