What characterizes mutualism in a relationship between two organisms?

Mutualism is characterized by interactions where both organisms involved benefit from the relationship. This can take various forms, such as providing food for each other, aiding in reproduction, or offering protection. An example of mutualism can be seen in the relationship between bees and flowering plants; bees receive nectar from the flowers, which serves as a food source, while the plants benefit from the pollination that bees provide, allowing them to reproduce.

In contrast, the other options describe different types of relationships. One organism benefiting while the other is harmed indicates parasitism, while both organisms not benefiting suggests either competition or a neutral relationship. Finally, when one organism is unaffected by the other, it describes commensalism, where one species benefits and the other is neither helped nor harmed. Thus, the defining feature of mutualism is the positive outcome for both organisms involved.