Which interaction benefits one organism at the expense of the other?

• A. Random Distribution
• B. Niche
• C. Parasitism
• D. Mutualism

Answer: (C)

Parasitism is an interaction in which one organism benefits while the other is harmed. The parasite gains nutrients or energy from the host, while the host bears a cost such as reduced growth, health, or reproductive success. This exactly describes a relationship where one party benefits at the expense of the other. For example, sea lice feeding on a fish injure the fish and gain resources in the process. In contrast, simple random distribution describes spacing, a niche describes an organism’s role in the environment, and mutualism is when both partners benefit, not when one benefits at the other’s expense.