Which statement differentiates a microorganism from a pathogen?

• A. A pathogen is a harmless microorganism.
• B. A microorganism is a tiny living thing; a pathogen is a microorganism capable of causing disease.
• C. A microorganism is only bacteria and viruses.
• D. A pathogen is non-living.

Answer: (B)

Microorganisms are microscopic living things that can be harmless, beneficial, or neutral. A pathogen is a microorganism that can cause disease. The key idea is disease-causing potential: being a microorganism doesn’t automatically mean it will cause illness, but a pathogen specifically refers to something that can cause disease. The statement that a pathogen is a microorganism capable of causing disease captures this distinction. The other choices don’t fit because they either claim pathogens are harmless, wrongly limit microorganisms to bacteria and viruses, or say pathogens are non-living, which isn’t accurate for many pathogens like bacteria and fungi.