Which of the following relationships is characterized as harmful to one organism?

The relationship characterized as harmful to one organism is parasitism. In this type of interaction, one organism, the parasite, benefits at the expense of the other organism, which is the host. The parasite usually derives nutrients and other benefits while harming the host in the process. This can lead to negative effects on the host’s health, growth, or survival.

In contrast, mutualism is a relationship where both organisms benefit, such as bees pollinating flowers. Commensalism involves one organism benefiting while the other is neither helped nor harmed, exemplified by barnacles that attach to whales. Cooperation refers to a relationship where both parties work together for mutual benefit, further highlighting the distinct negative impact that parasitism has on the host organism. Thus, parasitism is the correct answer as it explicitly denotes a harmful interaction for one of the involved organisms.