TOEFL Speaking Task 4 Practice 014Science

Narrator:Listen to part of a lecture in a Marine Biology class.

Professor:So we've talked a little about how fish use senses like vision, touch and so forth. But what I wanna talk about now is a special ability some fish have, the ability to produce electricity in their bodies. You're probably familiar with these fish, these fish that send out electric currents from their bodies naturally. So what's the purpose of this? Well, as you might expect, it can serve some important roles in helping fish survive. First, fish, like all animals, need food to survive. Well, the ability to produce electricity helps some fish to capture prey, you know, other organisms in the water that they eat. Take the electric eel, for example, the eel produces a strong electric current in its body. When the eel comes into contact with one of the smaller fish it depends on for food, the electric current that it sends out shocks the smaller fish and paralyzes it. It's not able to get away from the eel. The eel captures the fish easily and can eat it at its leisure. So this ability to use electricity to capture prey ensures that the eel gets the food it needs to survive. The ability to produce electricity also helps fish to successfully navigate their environment by detecting nearby objects. Some fish have poorly developed eyes, and the water they live in can be muddy and dark. Now there's a fish called the knifefish that produces electricity. This creates an electric field around the knifefish's body, when the knifefish swims close to, say a rock, it senses a disturbance and interference in its electric field. The fish then realizes that there is a rock nearby and that it has to avoid crashing into it. Once this happens, the knifefish swims away from the rock and thus avoids harming itself.