托福口语 Task 3

In biology, 'commensalism' is a type of symbiotic relationship between two species where one species benefits, and the other is neither helped nor harmed. The benefiting species often gains food, shelter, or transportation from the host species, while the host remains unaffected. This contrasts with mutualism, where both species benefit, and parasitism, where one species is harmed. Commensalism is common in nature, such as when smaller organisms attach to larger animals for mobility or use their leftovers as a food source.

Professor: Let me give you a clear example of commensalism from a marine environment. Consider the remora, a type of fish that attaches itself to a shark using a suction disk on its head. The remora gets free transportation—it can travel long distances without expending energy. It also feeds on scraps of food that the shark drops while eating its prey. So clearly, the remora benefits from this relationship. Now, what about the shark? The shark is not harmed because the remora is small and does not take any of the shark’s own food—it only eats the leftovers. The shark also doesn’t spend extra energy to carry the remora, since the remora simply holds on. And the shark doesn’t gain any advantage either—it doesn’t get cleaned or warned of danger. So the shark’s life is completely unaffected. This perfectly illustrates commensalism because one species, the remora, gains a clear advantage, while the other, the shark, is neither helped nor harmed.