During atrial systole, the tricuspid valve (P) ............... and semilunar valve (Q) ................

opens, closes

Reason — During atrial systole the atria contract and push blood into the ventricles, so the tricuspid and bicuspid valves open. The semilunar valves at the base of the pulmonary artery and aorta remain closed at this stage to prevent blood from flowing back into the ventricles.