Why are ventricles thicker than the atria?

The correct answer emphasizes the primary function of the ventricles, which are responsible for pumping blood out of the heart to the rest of the body. The ventricles, particularly the left ventricle, have thicker muscular walls compared to the atria because they need to generate significantly more pressure to overcome the resistance in the systemic circulation. This thick muscular layer allows the ventricles to contract forcefully, ensuring that blood can be effectively propelled through the aorta and into the arteries that supply the organs and tissues throughout the body. The thicker walls thus accommodate the demands of pumping blood over greater distances, as opposed to the atria, which only need to push blood into the ventricles.

The other options do not accurately describe the purpose of the ventricular thickness. While the atria do receive blood, holding blood is not their primary role, nor is it the specific reason for the differing wall thickness. Preventing backflow is managed by valves rather than wall thickness, making it less relevant in this context.