A biologist is studying blood vessels which have valves to prevent the backflow of blood. based on this information you would conclude that he or she is studying

The biologist is studying the atria and the ventricles of the heart. The heart is made up of four chambers; two atria upper chambers and two ventricles lower chambers. Each of the chamber has a valve through which the blood passes before existing the chamber. The valves prevent the blood from flowing backward.