Which system in the body is responsible for transporting substances?

The circulatory system is the key system in the body responsible for transporting various substances, including oxygen, nutrients, hormones, and waste products. It consists of the heart, blood vessels, and blood. The heart pumps blood through a network of arteries, veins, and capillaries, ensuring that vital substances reach different parts of the body where they are needed.

In contrast, the respiratory system is primarily involved in the exchange of gases, facilitating the intake of oxygen and the removal of carbon dioxide. The digestive system focuses on the breakdown of food, allowing nutrients to be absorbed into the bloodstream, but it is not directly responsible for the transportation of substances throughout the body. The nervous system is responsible for transmitting signals and coordinating actions but does not transport substances like the circulatory system does. Thus, the circulatory system plays a fundamental role in the distribution and transportation of essential substances, making it the correct choice.