Which of the following is an example of parasitism?

• A. A parasite on a lion
• B. A bird eating bacteria off a lion
• C. A fish swimming on a sea urchin
• D. A lion hunting zebra

Answer: (A)

Parasitism is when one species benefits by using another species as a host, while the host is harmed in the process. A parasite on a lion fits this: the parasite gains nutrients or a habitat, and the lion is harmed or burdened by hosting it. The other scenarios don’t match parasitism. A bird that eats bacteria off a lion is an example of cleaning symbiosis, where the bird gets a meal and the lion often benefits from being cleaner. A fish riding on a sea urchin is typically a commensal relationship, where the fish gains transport or shelter and the urchin is largely unaffected. A lion hunting zebra is predation, a predator–prey interaction, not parasitism.