A chemical that kills bacteria or slows their growth without harming body cells is called what?

• A. Antibiotic
• B. Virus
• C. Microorganism
• D. Disease agent

Answer: (A)

The main idea here is selective toxicity—the ability of a substance to attack bacteria without harming human cells. An antibiotic is a chemical designed to do just that: kill bacteria or slow their growth while sparing the body's own cells.

That’s why this option fits best. The other terms describe broader concepts rather than a drug with a specific selective effect. A virus is a type of infectious agent, not a chemical that treats infections. A microorganism is any microscopic organism (bacteria, fungi, viruses, etc.), not a treatment. A disease agent is a general label for anything that can cause disease, not the specific class of drugs used to treat bacterial infections.

In practice, antibiotics exploit differences between bacterial and human cells—such as bacterial cell wall synthesis or bacterial protein production—to inhibit bacteria with minimal harm to the host. This distinction is what makes antibiotics the correct choice.