TOEFL Speaking Task 3

In biology, the concept of 'commensalism' refers to a symbiotic relationship between two species in which one species benefits while the other is neither helped nor harmed. The benefiting species often gains food, shelter, or transportation from the host, but the host remains unaffected. This differs from mutualism, where both species benefit, and parasitism, where one species harms the other. Commensalism is common in nature and can be observed in various ecosystems, such as marine environments and forests.

Professor: Let me give you a clear example of commensalism from the ocean. Consider the remora, a type of fish that attaches itself to a shark using a suction disk on its head. The remora feeds on leftover food scraps from the shark's meals—bits of fish and other prey that the shark drops while eating. The remora gets a reliable food source and also free transportation, as it hitches a ride on the shark to travel across the ocean. But what about the shark? Well, the shark doesn't benefit from this arrangement, but it also isn't harmed. The remora is too small to affect the shark's swimming or feeding, and it doesn't take any food directly from the shark's mouth. So the shark simply ignores the remora. This relationship perfectly illustrates commensalism: one species benefits, the other is unaffected.