Final answer:
The P wave on an electrocardiogram (ECG) represents the depolarization of cells in the atria (Option B).
Step-by-step explanation:
The P wave on an electrocardiogram (ECG) represents the depolarization of cells in the atria. When the sinoatrial (SA) node initiates an electrical impulse, it causes the myocardial cells in the atria to depolarize. This electrical activity results in the P wave seen on an ECG and leads to the contraction of the atria, pushing blood into the ventricles.
It is important to note that the depolarization of cells in the SA node, the pacemaker of the heart, triggers the depolarization of the atria but is not represented as the P wave.
Similarly, the atrioventricular (AV) node and ventricles have their electrical activities represented by other parts of the ECG, with the AV node delay being part of the PR interval, and the ventricles' depolarization forming the QRS complex.
Thus, the correct option is B.