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

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

Answer: (D)

One organism benefiting while the other remains unaffected describes commensalism. In this type of relationship, the benefiting species gains something it needs—like a place to live, transport, or access to food—while the other species experiences no real gain or harm. A classic example is barnacles attaching to a whale: the barnacles get a free ride and access to food particles as the whale moves, but the whale is not helped or hurt in any meaningful way. Another example is an epiphytic plant growing on a tree; the plant gets support and better exposure to light, while the tree is largely unaffected. This differs from parasitism, where the host is harmed, and from mutualism, where both partners benefit. The broader term “symbiotic” simply means living together and includes several types, not the one-sided benefit described here. So the relationship described is commensalism.