Final answer:
In biology, the rapid filling phase refers to the early stage of the ventricular diastole in the cardiac cycle, where blood passively fills the relaxing ventricles quickly due to a pressure gradient.
Step-by-step explanation:
The term ‘rapid filling phase’ is typically associated with the cardiac cycle in Biology, specifically concerning the functions of the heart. During the cardiac cycle, the rapid filling phase refers to the initial stage of diastole when the ventricles are filling with blood.
Following atrial systole (contraction of the atria), the ventricles relax (ventricular diastole), and the increase in volume and corresponding decrease in pressure causes blood to rush into the ventricles from the atria. This phase is characterized by a quick passive flow of blood due to the pressure gradient without any muscular contraction, which is why it's called ‘rapid filling.’
It is a crucial part of the cardiac cycle because it ensures that a sufficient volume of blood is available for the next contraction, which will be pumped out to the body (left ventricle) and to the lungs (right ventricle).