Power Supply Filter detection using Zener diode and PNP Transistor
Why do we have resistors connected to the anode and cathode of the Zener diode? What purpose do the top and bottom resistor serve.


I recommend looking at basic Zener circuitrs to answer that, that'll clear up a lot of your other questions, too. Short answer: 

Because without any serious resistor, the current through the diode would not be limited when the voltage exceeds the Zener voltage, and the diode will burn out.