What type of relationship exists where one species benefits and the other neither benefits nor is harmed?

The correct answer is commensalism, which describes a specific type of interaction between two species where one species benefits while the other is neither helped nor harmed. This means that in a commensal relationship, one organism may gain food, shelter, or some other benefit from its interaction with another species, while the other organism is unaffected by this relationship.

For instance, a classic example of commensalism is barnacles attaching to the shell of a turtle. The barnacles benefit by gaining a place to live and access to nutrients in the water, while the turtle does not experience significant effects from the barnacles being there.

Other types of relationships, such as parasitism, involve one species benefiting at the expense of the other, as seen in parasites who live on or in a host and derive nutrients to the host's detriment. Mutualism, on the other hand, describes interactions in which both species involved benefit from the relationship, like bees pollinating flowers while gathering nectar. Competition occurs when two species vie for the same resources, resulting in a negative impact on at least one of the species. Each of these other types of interactions has different implications for the species involved, further highlighting the uniqueness of commensalism.