What do both the circulatory and respiratory systems work to circulate?

The circulatory and respiratory systems collaboratively circulate carbon dioxide and oxygen throughout the body. The primary function of the respiratory system is to facilitate gas exchange, wherein oxygen from the atmosphere enters the lungs and carbon dioxide, a waste product of metabolism, is expelled. Once oxygen is absorbed into the bloodstream, the circulatory system transports it to cells and tissues that require it for energy production and various metabolic processes.

While the circulatory system plays a crucial role in distributing several substances, including nutrients and waste products, the specific focus of both the circulatory and respiratory systems in the context of this question is the exchange and transport of gases—particularly carbon dioxide and oxygen. Thus, the correct response underscores the essential function shared by both systems in maintaining homeostasis and supporting cellular respiration.