In commensalism, which statement is true?

• A. Both benefit
• B. One benefits, the other harmed
• C. One benefits, the other unaffected
• D. Neither benefits

Answer: (C)

In commensalism, one species benefits while the other is unaffected. This means the benefitting organism gains a resource, transportation, or shelter, while the partner experiences no real advantage or harm. For example, remoras hitching a ride on sharks use scraps of food left behind and don’t noticeably help or hurt the shark. Similarly, barnacles on whales gain a nutrient-rich path through water, with little or no effect on the whale.

So the true statement is that one organism benefits and the other remains unaffected. If both benefited, it would be a mutualistic relationship; if one benefited and the other was harmed, that would be parasitism. If neither benefited, that would be neutral or a different, less common type of interaction.