Define external parasites.

Define external parasites.

• A. Organisms that photosynthesize to obtain energy.
• B. Organisms that grow and feed on other living organisms, which are referred to as hosts.
• C. Bacteria that cause infections.
• D. Viruses that invade cells.

Answer: (B)

External parasites are organisms that rely on a host for survival by living on the outside of that host and feeding off it. They attach to the surface, such as on the skin or hair, and obtain nutrients without entering the host’s body. This relationship—parasite on the exterior using the host for resources—defines why the best description is the one that describes organisms that grow and feed on other living organisms, which are referred to as hosts. The other options describe organisms that are not external parasites: photosynthesizers that make their own energy, bacteria that cause infections (not necessarily parasites), and viruses that invade cells (intracellular parasites, not external ones).

External parasites are organisms that rely on a host for survival by living on the outside of that host and feeding off it. They attach to the surface, such as on the skin or hair, and obtain nutrients without entering the host’s body. This relationship—parasite on the exterior using the host for resources—defines why the best description is the one that describes organisms that grow and feed on other living organisms, which are referred to as hosts. The other options describe organisms that are not external parasites: photosynthesizers that make their own energy, bacteria that cause infections (not necessarily parasites), and viruses that invade cells (intracellular parasites, not external ones).