A Level Biology Practice Exam

What does the cardiac cycle encompass?

1. The hormonal changes during fetal development

2. The events of a single heartbeat

3. The flow of blood through the lungs

4. The electrical activity of nerve cells

The correct answer is: The events of a single heartbeat

The cardiac cycle refers specifically to the series of events that take place during a single heartbeat, encompassing both the contraction and relaxation phases of the heart. This cycle includes two main phases: systole, when the heart muscles contract to pump blood out of the chambers, and diastole, when the heart muscles relax, allowing the chambers to fill with blood. During this cycle, critical events such as the closing and opening of heart valves occur, facilitating the flow of blood through the heart and into the circulatory system. While the other options mention biological processes, they do not relate to the cardiac cycle. The hormonal changes during fetal development involve hormonal regulation and changes in response to growth factors, which is distinct from cardiac function. The flow of blood through the lungs pertains to pulmonary circulation, a specific aspect of the circulatory system rather than the full cycle of the heart’s activity. Lastly, the electrical activity of nerve cells (neurotransmission) is primarily connected to the nervous system, not the sequence of heart functions involved in pumping blood. Thus, the choice highlighting the events of a single heartbeat accurately reflects the scope of the cardiac cycle.