IB Biology Exam Prep

Answer: B, Parasitism. The helminthes prospered at the expense of the mice, resulting in a parasitic relationship.

Key Takeaway: Parasitism occurs in a relationship between organisms when one organism benefits at the expense of others. This is distinct from commensalism and mutualism. In commensalism, one organism prospers without any positive or negative effect on the other. In mutualism, both organisms benefit from the relationship.