Question

why openings of auricles and ventricles are guarded by valves

Answer 1

These are present to prevent the backward flow of blood

Answer 2

Openings of auricles and ventricles are guarded by valves due to following reasons :-
1. it provides a way to flow the blood
2.it provides the blood in the specific time when required
3.it also provides the blood to that part in a limited amount .

hope it helps