Final answer:
The electrical power for APU ignition and start control circuits is typically provided by the aircraft's batteries or ground power.
Step-by-step explanation:
The Auxiliary Power Unit (APU) is an essential component of modern aircraft, providing necessary power when the main engines are not running.
The electrical power for APU ignition and start control circuits is usually provided by the aircraft's batteries or ground power when the aircraft is on the ground.
Once the APU is operational, it can generate its own electrical power to sustain its systems and, additionally, supply power to the aircraft's electrical systems, air conditioning, and other functions as required.