Chapter 23, Problem 89MSPP

The voltage produced by a single nerve or muscle cell is quite small, but there are many species of fish that use multiple action potentials in series to produce significant voltages. The electric organs in these fish are composed of specialized disk-shaped cells called electrocytes. The cell at rest has the usual potential difference between the inside and the outside, but the net potential difference across the cell is zero. An electrocyte is connected to nerve fibers that initially trigger a depolarization in one side of the cell but not the other. For the very short time of this depolarization, there is a net potential difference across the cell, as shown in Figure P23.86. Stacks of these cells connected in series can produce a large total voltage. Each stack can produce a small current; for more total current, more stacks are needed, connected in parallel.

Figure P23.86

The electric catfish is another electric fish that produces a voltage pulse by means of stacks of electrocytes. As the fish grows in length, the magnitude of the voltage pulse the fish produces grows as well. The best explanation for this change is that, as the fish grows,

A. The voltage produced by each electrocyte increases.

B. More electrocytes are added to each stack.

C. More stacks of electrocytes are added in parallel to the exist­ing stacks.

D. The thickness of the electrocytes increases.