What term describes organisms that live on or obtain nutrients from another organism?

• A. External parasites
• B. Contagions
• C. Pediculosis
• D. Syphilis

Answer: (A)

External parasites describe organisms that live on the surface of another organism and obtain nutrients from it. This wording captures the idea of living on or drawing nourishment from a host, which is exactly what these organisms do. Contagions are disease-causing agents that spread between hosts, pediculosis is the condition of being infested by lice, and syphilis is a specific infectious disease; none of these define the general relationship of living on or feeding from another organism like external parasites do.