A Level Biology Practice Exam

During which phase of the cardiac cycle do the atria contract?

1. Diastole

2. Systole

3. Resting phase

4. Recovery phase

The correct answer is: Systole

During the cardiac cycle, the atria contract during the systole phase. This phase is primarily characterized by the contraction of the heart chambers. Specifically, atrial systole follows the phase of ventricular filling, where blood is pushed from the atria into the ventricles. This contraction helps to ensure that the ventricles are filled with a maximum volume of blood before they subsequently contract during their own systole phase. In contrast, diastole refers to the phase when the heart muscles relax, allowing the chambers to fill with blood. The resting phase implies a period of inactivity in terms of contraction, while the recovery phase is generally not a term used to describe any part of the cardiac cycle. Thus, the atria contracting during systole is critical for effective blood circulation and maintaining proper heart function.