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 species that benefits often gains food, shelter, or transportation, while the host species remains unaffected in terms of survival or reproduction. Commensalism is distinct from mutualism, where both species benefit, and parasitism, where one species is harmed. This relationship can be observed in various ecosystems, where organisms exploit the presence or activities of another species without causing significant impact.

Professor: Let me give you a classic example of commensalism. Consider the remora, a type of fish that attaches itself to larger marine animals, like sharks or manta rays. The remora has a specialized suction disk on top of its head, which it uses to cling to the host. As the shark swims, the remora gets free transportation, allowing it to travel long distances without expending much energy. Additionally, the remora feeds on scraps of food left over from the shark's meals. When the shark tears apart its prey, small bits of flesh drift away, and the remora eats these leftovers. The shark, however, is not harmed by the remora's presence—it doesn’t lose any significant nutrition, nor is it slowed down. The shark simply goes about its business as if the remora were not there. So, the remora clearly benefits, while the shark is unaffected.