Final answer:
A check valve is a valve that allows flow in one direction only, and it is present in the cardiovascular system to ensure the one-way flow of blood. Both veins and arteries have valves to prevent the backflow of blood.
Step-by-step explanation:
A check valve is a valve that allows flow in one direction only. In the cardiovascular system, valves in the heart and vessels ensure the one-way flow of blood. They open to allow blood to move forward and then close to prevent backward flow. Both veins and arteries have valves to prevent the backflow of blood.