Which statement correctly describes bacteria?

• A. Bacteria are one-celled organisms that multiply and may produce toxins that damage tissues.
• B. Bacteria are multicellular organisms that require a host to survive.
• C. Bacteria are non-living infectious agents.
• D. Bacteria always cause disease in every infection.

Answer: (A)

Bacteria are single-celled, living organisms that multiply, and many species can produce toxins that damage tissues. This combination explains why bacteria can cause illness—their one-cell structure makes them simple yet capable of rapid growth, and toxin production can directly harm cells or disrupt normal tissue function. They are not multicellular organisms that must live in a host; rather, many bacteria can survive independently in a wide range of environments. They are living organisms, not non-living infectious agents, and their effects vary: some bacteria cause disease, while many are harmless or beneficial. They do not always cause disease—infections can be mild, asymptomatic, or prevented by the immune system and treatments.