OCR General Certificate of Secondary Education (GCSE) Biology Practice Exam

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What initiates the flow of blood into the ventricles?

Contraction of the atria
Relaxation of the arteries
Blood pressure from the veins
Contraction of the ventricles

The correct answer is: Contraction of the atria

The flow of blood into the ventricles is initiated by the contraction of the atria. During the cardiac cycle, when the atria contract, they push blood into the ventricles. This contraction increases the pressure within the atria, forcing the atrioventricular valves (the valves between the atria and the ventricles) to open, allowing blood to flow from the atria into the ventricles. This process is essential for ensuring that the ventricles are filled with an adequate volume of blood before they contract and pump blood out to the lungs and the rest of the body. Understanding the roles of different heart chambers and their actions is crucial in grasping how the circulatory system functions effectively. The other options do not directly initiate the flow of blood into the ventricles; for instance, relaxation of the arteries pertains to the flow of blood from the heart rather than into it, while contraction of the ventricles actually occurs after the ventricles have filled with blood, maintaining an orderly sequence in the cardiac cycle.