Which statement best defines a toxin?

• A. A poison is any substance that can harm the body
• B. A toxin is a poisonous substance secreted by bacteria, plants, or animals
• C. A toxin is any chemical that can harm the body
• D. A toxin is a synthetic chemical with no biological origin

Answer: (B)

A toxin is a poisonous substance produced by living organisms. It is specifically made by biological sources such as bacteria, plants, or animals and is often released or secreted to exert its harmful effect. This biological origin is what sets toxins apart from other harmful substances. Examples include botulinum toxin from bacteria, venom in snake or spider bites, and plant toxins like ricin from castor beans.

The idea that a poison is any substance that can harm the body is too broad because it includes many non-biological substances that aren’t produced by living organisms. Likewise, defining a toxin as any chemical that can harm the body widens the term beyond its biological origin, which isn’t accurate for the standard definition. And calling toxins synthetic chemicals with no biological origin conflicts with the core idea that toxins arise from living organisms.