Which term describes a relationship in which one species benefits at the expense of the other?

• A. Parasitism
• B. Mutualism
• C. Commensalism
• D. Predation

Answer: (A)

The concept being tested is how organisms interact when one benefits at the other’s expense. In parasitism, the parasite gains nutrients, habitat, or a boost to its survival, while the host incurs costs such as reduced growth, health problems, or lower fitness. This relationship is typically long-term and does not rely on immediately killing the host, unlike predation where the predator hunts and consumes the prey. It also differs from mutualism, where both species benefit, and commensalism, where one benefits and the other is largely unaffected. So the best term for a relationship where one species benefits at the expense of the other is parasitism.