Which interaction describes one species benefiting while the other is unaffected?

• A. Parasitism one benefits at the expense of the other (e.g., tapeworm)
• B. Mutualism both benefit (e.g., bees and flowers)
• C. Commensalism one benefits, the other unaffected (e.g., barnacles on whales)
• D. Competition for resources

Answer: (C)

Commensalism is when one species benefits and the other is unaffected. For example, barnacles on a whale gain a place to live and better access to water flow for feeding as the whale moves, while the whale is not helped or harmed in any meaningful way. This sits in contrast to parasitism, where the parasite benefits at the host’s expense (like a tapeworm), mutualism, where both partners benefit (bees and flowers), and competition for resources, where both suffer from limited resources.