Which statement best defines a microorganism?

Which statement best defines a microorganism?

• A. An organism that is too small to see with the naked eye
• B. A non-living chemical compound
• C. An inert particle
• D. A large multicellular organism

Answer: (A)

The main idea is that a microorganism is a living thing that is so small it cannot be seen with the naked eye. This captures two essential aspects: it is alive and it requires magnification to observe. Microorganisms include bacteria, fungi, algae, protozoa, and many microscopic parasites, which you typically study with a microscope. The other statements describe things that aren’t living, aren’t observed under magnification, or are large enough to see without aid, so they don’t fit the definition. That combination—life plus being too small to see unaided—best defines a microorganism.

The main idea is that a microorganism is a living thing that is so small it cannot be seen with the naked eye. This captures two essential aspects: it is alive and it requires magnification to observe. Microorganisms include bacteria, fungi, algae, protozoa, and many microscopic parasites, which you typically study with a microscope. The other statements describe things that aren’t living, aren’t observed under magnification, or are large enough to see without aid, so they don’t fit the definition. That combination—life plus being too small to see unaided—best defines a microorganism.