We used measurement of the resistive (in-phase) component of the impedance with a single-chip lock-in amplifier, AC-coupled to detect current pulses associated with the zoospore transit. The integration time of the lock-in amplifier determines the time response. The value needed to get the necessary signal/noise is determined by the measurement frequency. If the measurement frequency were low, then the impedance would be dominated by the interfacial double-layer capacitances, CDL (Figure ). If the measurement frequency were high then the stray capacitance, C, and the zoospore membrane capacitance, CM, would act as short circuits so the zoospore would be undetectable.