Written by the Fiveable Content Team • Last updated September 2025
Verified for the 2026 exam
Verified for the 2026 exam•Written by the Fiveable Content Team • Last updated September 2025
Definition
Parasitism is a type of symbiotic relationship between two organisms where one organism (the parasite) benefits at the expense of the other (the host). The parasite derives nutrients from the host, often causing harm in the process.
Related terms
Host: In biology, a host is an organism that harbors another organism inside or near their body in a symbiotic relationship. It's like the house in our analogy.
Symbiosis is any type of close and long-term biological interaction between two different biological organisms. It's like having roommates - some are beneficial (mutualistic), some are neutral (commensal), and some are harmful (parasitic).
Ectoparasite: An ectoparasite is a parasite that lives on the surface of its host. They're similar to that freeloader roommate who always hangs out in your living room but never contributes to rent or utilities.