What type of circulation involves blood passing through the heart twice during a complete circuit of the body?

Double circulation is a system in which blood passes through the heart two times during one complete circuit of the body. In this system, blood is separated into two circuits: the pulmonary circuit, where deoxygenated blood is carried from the heart to the lungs and back, and the systemic circuit, where oxygenated blood is distributed from the heart to the rest of the body.

This separation allows for more efficient oxygenation of blood, as the body can maintain higher blood pressure in the systemic circuit, providing organs with a more substantial supply of oxygen and nutrients. This mechanism is crucial for more complex organisms, such as mammals, as it supports their higher metabolic demands.

In contrast, single circulation entails blood traveling through the heart only once per circuit, resulting in lower pressure and less efficient oxygen delivery. Open circulation, seen in some invertebrates, lacks a closed network of blood vessels, which again is different from the direct structure of double circulation. Closed circulation, while it does involve blood and vessels, does not specify the need for blood to pass through the heart twice.