In which type of symbiotic relationship does one species benefit and the other is harmed?

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

Answer: (D)

This question is about a relationship where one organism benefits at the expense of another. That pattern is parasitism, a type of symbiotic relationship. The parasite gains nutrients, shelter, or a habitat by living on or inside the host, while the host is harmed in the process. Think of fleas on a dog, ticks feeding on blood, or a tapeworm living in the digestive system—the parasite benefits and the host bears the cost.

By comparison, mutualism is when both partners benefit (like bees getting nectar and helping flowers get pollinated), and commensalism is when one benefits and the other is largely unaffected (like barnacles on a whale). The word symbiotic just means close living together, and parasitism is the specific form where one benefits and the other is harmed.