What is a key characteristic of a parasite?

A key characteristic of a parasite is that it typically harms its host as it derives nutrients at the host's expense. Parasites can cause a variety of negative effects ranging from mild discomfort to severe health issues in their hosts. This relationship is often one-sided, as the parasite benefits while the host suffers.

Unlike mutualistic relationships where both parties benefit, parasitism is characterized by this detrimental impact on the host. This contrasts with the other options, which suggest positive interactions or benefits to the host, such as enhancing survival or growth, or living symbiotically, none of which accurately describe the fundamental nature of parasitism.