Fish respiratory systems exchange gas and receive oxygen at the gills. This oxygen then enters the bloodstream and is pumped through the heart and back through the gills without first returning to the heart. This order of events best describes which type of circulation system?

Gas exchange between tissues and the blood is an essential function of the circulatory. The air contains oxygen that crosses the lung tissue, enters the bloodstream, and the alveoli are in direct contact with capillaries of the circulatory system. As water flows over the gills, oxygen is transferred to blood via the veins.