Which term describes the relationship where one species benefits while the other is unaffected?

The term that describes the relationship where one species benefits while the other is unaffected is commensalism. In this type of interaction, one organism derives benefits, such as food or shelter, from the other organism without causing harm or providing any reciprocal benefit. An example of commensalism is barnacles attaching to the shell of a turtle; the barnacles gain a mode of transportation and access to feeding opportunities, while the turtle remains largely unaffected by their presence.

In contrast, mutualism involves both species benefiting from the relationship, while amensalism refers to a relationship where one organism is harmed and the other is unaffected. Neutralism denotes interactions where both species coexist without impacting each other significantly. Commensalism is specifically characterized by the unidirectional benefit, which is why it is the correct choice in this context.