Chapter 20, Problem 103PP

BIO The Electric Eel

Of the many unique and unusual animals that inhabit the rainforests of South America, one stands out because of its mastery of electricity. The electric eel (Electrophorus electricus), one of the few creatures on Earth able to generate, store, and discharge electricity, can deliver a powerful series of high-voltage discharges reaching 650 V. These jolts of electricity are so strong, in fact, that electric eels have been known to topple a horse crossing a stream 20 feet away, and to cause respiratory paralysis, cardiac arrhythmia, and even death in humans. Though similar in appearance to an eel, the electric “eel” is actually more closely related to catfish. They are found primarily in the Amazon and Orinoco river basins, where they navigate the slow-moving, muddy water with low-voltage electric organ discharges (EOD), saving the high-voltage EODs for stunning prey and defending against predators. Obligate air breathers, electric eels obtain about 80% of their oxygen by gulping air at the water’s surface. Even so, they are able to attain lengths of 2.5 m and a mass of 20 kg.

The organs that produce the eel’s electricity take up most of its body, and consist of thousands of modified muscle cells—called electroplaques—stacked together like the cells in a battery. Each electroplaque is capable of generating a voltage of 0.15 V, and together they produce a positive charge near the head of the eel and a negative charge near its tail.

• Electric eels produce an electric field within their body. In which direction does the electric field point?

1. A. toward the head
2. B. toward the tail
3. C. upward
4. D. downward