What best describes bacteria?

• A. Intracellular parasites that require living host cells to replicate.
• B. Multicellular organisms with tissues.
• C. Unicellular organisms that cause disease by invading host tissues or by producing toxins.
• D. Non-living infectious particles.

Answer: (C)

Bacteria are unicellular prokaryotes, meaning their cells lack a true nucleus and membrane-bound organelles, yet they can grow and reproduce on their own. Some bacteria cause disease by invading host tissues or by producing toxins that damage cells or disrupt normal functions. This living, single-celled nature plus their ability to harm through invasion or toxin production is what best describes them. They’re not intracellular parasites that require living host cells to replicate (that describes viruses), they’re not multicellular organisms with tissues, and they’re not non-living infectious particles.