In which type of relationship does one organism benefit while the other is harmed?

In the context of ecological relationships, parasitism is characterized by one organism, the parasite, deriving benefit at the expense of the other organism, the host, which suffers harm as a result. This interaction often results in the parasite gaining nutrients or resources while negatively impacting the host's health or viability.

An example of parasitism is when a tick attaches itself to a mammal, feeding on its blood, which can lead to various health issues for the host, such as disease transmission or blood loss.

The other types of relationships do not fit this description of benefit-and-harm dynamics. In mutualism, both organisms benefit; in commensalism, one benefits while the other is neither helped nor harmed; and in neutralism, neither organism is significantly affected. This contrast clarifies why parasitism is the type of relationship where one organism benefits and the other is harmed.