The ventricle has thicker, more muscular walls than the atria. Relate this difference in wall structure to the functions of the 2 types of heart chamber.

The atria of the heart merely need to allow blood to flow into the ventricle, and therefore aren't very muscular.

The ventricles of the heart need to actually pump blood to the rest of the body, whether to the lungs or the the rest of the body.

Ventricle has to pump blood

Atria has to store blood