An organism that lives in or on a host causing harm is called what?

• A. Predator
• B. Commensal
• C. Parasite
• D. Mutualist

Answer: (C)

Parasitism is a relationship in which an organism, the parasite, lives on or inside another organism—the host—and gains nutrients or other resources at the host’s expense. This typically harms the host, either by depriving it of resources or causing damage or disease. Examples include tapeworms living in the intestine, ticks on the skin, or the Plasmodium parasite in red blood cells. This differs from predation, where the predator kills and consumes its prey, from commensal relationships where one partner benefits without harming the other, and from mutualism where both partners benefit. So, the term that fits the description is parasite.