Electric discharge by eels In several aquatic animals, such as the South American el...

Electric discharge by eels In several aquatic animals, such as the South American electric eel, electric organs produce 600 -V potential difference pulses to ward off predators as well as to stun prey. Figure 15.31 illustrates the key component that produces this electric shock—an electrocyte. The interior of an inactive electrocyte (Figure 15.31a) has an excess of negatively charged ions. The exterior has an excess of positively charged sodium ions 1Na+2 on the left side and positively charged potassium ions (K⁺) on the right. There is a -90-mV electric potential difference from outside the cell membrane to inside the electrocyte cell membrane, but zero potential from one exterior side to the other exterior side. How then does an eel produce the 600-V potential difference necessary to stun an intruder? The eel’s long trunk and tail contain many electrocytes placed one after the other in columns (Figures 15.31b and c). Each electrocyte contains several types of ion channels, which when

channels on the left flat side of each electrocyte from outside the cell to the inside. This causes the electric potential across that cell membrane to change from -90 mV to +50 mV. The electric potential from the left external side to the right external side of an electrocyte is now about 100 mV (Figure 15.31c). With about 6000 electrocytes placed one after the other (in series), the eel is able to produce an electric impulse of over 600 V (6000 electrocytes in series times 0.10 V per electrocyte). The discharge lasts about 2–3 ms.

Suppose that one cell of the electrocyte is regarded as a small capacitor with a 0.10-V potential difference across it. How should we arrange 10 cells to get a 1.0-V potential difference across them?

(a) In series , as in Figure P15.67a

(b) In parallel, as in Figure P15.67b

(c) Randomly so that they do not cancel each other

(d) Not enough information