Cellulose-digesting microorganisms live in the guts of termites and ruminant mammals. This relationship is an example of _____.

• A. Parasitism
• B. Predation
• C. Mutualism
• D. Commensalism

Answer: (C)

A mutualistic relationship is being tested here. The termites and ruminant mammals rely on gut-dwelling microorganisms to digest cellulose, something the host animals can’t do on their own. In return, the microbes get a steady habitat and a constant food supply, along with a favorable environment for growth. This two-way benefit means both partners gain: the host obtains energy from the breakdown products of cellulose, and the microbes receive protection and nutrients. It’s not parasitism because the host isn’t harmed, not predation since there’s no one organism preying on the other, and not commensalism because both organisms benefit rather than only one.