What defines parasitism in a symbiotic relationship?

Parasitism is defined by the interaction where one organism, the parasite, derives benefit at the expense of the other organism, known as the host. In this relationship, the parasite obtains nutrients or some other form of advantage from the host, which can lead to harm or detriment to the host's health, well-being, or survival. This dynamic showcases how the different organisms can have opposing effects on each other; one gains an advantage, while the other suffers consequences.

For instance, think about how a tapeworm lives in the intestines of a mammal, absorbing nutrients meant for the host. While the tapeworm thrives, the host may suffer from malnutrition or other health issues because the parasite takes away resources it needs.

In contrast, the other options do not accurately capture the essence of parasitism. Mutualism would describe a relationship where both organisms benefit, while commensalism suggests one benefits and the other is unaffected, and a relationship where neither benefits does not fit the definition of any typical symbiotic interaction.