Which statement defines a toxin?

• A. A toxic substance made by living organisms including reptiles, insects, plants and microorganisms
• B. A synthetic chemical used to kill pests
• C. A substance that only affects plants
• D. A substance that is harmless to humans

Answer: (A)

A toxin is a poisonous substance produced by living organisms. This statement captures that idea by pointing to toxins as substances generated by living beings, including reptiles, insects, plants, and microorganisms. Toxins are natural poisons, not necessarily synthetic chemicals, which helps distinguish them from toxicants that are man-made. It’s also not limited to affecting only plants—toxins can harm a wide range of organisms, including humans, animals, and other plants, often at very low doses. Examples include snake venom, botulinum toxin from bacteria, and plant toxins like ricin. The described definition thus aligns with how toxins are understood in biology and toxicology.