CSET Multiple Subjects Subtest 2: Math and Science Practice Test

Symbiotic relationships are classified by how they affect the participants, especially the host. In commensalism, one partner benefits while the host is essentially unaffected, a neutral impact on the host. For example, barnacles attach to a whale: the barnacles gain access to nutrients and transport, while the whale isn’t helped or harmed.

Mutualism would give both partners a benefit, so the host would not be neutral. Parasitism hurts the host, which rules it out for neutral. Amensalism involves one species being harmed while the other is unaffected, which is different from a neutral effect on the host in the typical sense. So the correct type is commensalism.