While I was reading my notes on Electrochemistry, I found a cell attached to the main circuit in an electrolytic cell which perform electrolysis. What does this cell do there ? Does it create polarity on the platinum electrodes to attract the ions in the solution for oxidation or reduction or does it actually participate in electrolysis by supplying electrons. If the former is the case, then why do we write EFFICIENCY OF AN ELECTROLYTIC CELL = ( Charge Used) / ( Charged passed ) because only external cell has the capability to pass charges through the circuit. I mean what does the cell do there..... ???