The primary role of circulatory systems in multicellular organisms is to transport essential substances throughout the body. This includes the movement of nutrients, gases like oxygen and carbon dioxide, hormones, and waste products. The circulatory system enables efficient distribution due to the high metabolic demands of multicellular life. It consists of a network of blood vessels and the heart, driving blood circulation and ensuring that cells receive the resources needed for energy production and functioning. Efficient circulation is crucial for maintaining homeostasis.