What is a characteristic of a single circulation system?

A characteristic of a single circulation system is that blood goes directly from the heart to the gills and then to the body tissues. In organisms with this system, such as fish, there is only one circuit through which the blood flows. After leaving the heart, blood is directed to the gills where it is oxygenated, and subsequently, it travels to the rest of the body to deliver that oxygen to tissues. This process highlights the efficiency of the single circulation pathway, allowing for a direct route for oxygenated blood to reach bodily tissues immediately after it has been oxygenated at the gills.

In contrast, a double circulation system, which is found in mammals and some other animals, involves two distinct circuits—one for oxygenation in the lungs and another for delivering oxygenated blood to the body. Additionally, the statement regarding separation of oxygenated and deoxygenated blood applies to double circulation systems but not to single circulation systems, where such separation does not exist. Lastly, single circulation systems are not exclusive to mammals, as they are primarily seen in many aquatic animals like fish.