What type of relationship occurs when one organism benefits while the other is unaffected?

The correct answer is commensalism, which is a type of symbiotic relationship where one organism benefits while the other is neither helped nor harmed. In these interactions, one species gains some advantage, such as food or shelter, while the other species remains neutral and is unaffected by the relationship.

An example of commensalism can be observed in barnacles that attach themselves to the shell of a tortoise. The barnacles benefit by gaining a place to live and access to nutrient-rich water, while the tortoise remains indifferent to their presence.

In contrast, mutualism involves both organisms benefiting from the relationship, such as bees pollinating flowers while obtaining nectar, and parasitism where one organism benefits at the expense of another, like a tick feeding on a host. Interference doesn't describe a specific symbiotic relationship and generally refers to competition between organisms. Thus, commensalism is clearly the appropriate term for the relationship described in the question.