Which term describes an organism living off a host?

• A. Parasite
• B. Virus
• C. Bacteria
• D. Fungus

Answer: (A)

Living off a host describes parasitism, a relationship in which one organism depends on another for nutrients and habitat, often causing harm to the host. The organism that lives off the host is a parasite, encompassing creatures that spend time on the outside (like fleas or ticks) or inside (like certain worms) the host. This term best captures the idea of relying on and benefiting from another organism's resources at the host’s expense.

Other options involve organisms with broader lifestyles: some viruses require a host cell to reproduce and are sometimes considered parasites of cells, while bacteria and fungi include many free-living or non-parasitic forms. But the general term that describes living off a host is parasite.