Final answer:
The QRS complex arises from ventricular depolarization and represents the electrical activity of the ventricles contracting and pumping blood to the lungs and body.
Step-by-step explanation:
The QRS complex arises from ventricular depolarization. It represents the electrical activity of the ventricles contracting and pumping blood to the lungs and body. The QRS complex is the largest and most prominent part of the ECG waveform, indicating the strong electrical signal required for ventricular depolarization. The repolarization of the atria occurs during the QRS complex, which is why it is not separately visible on an ECG.