What type of circulation system is characterized by blood passing through the gills before it reaches the rest of the body?

The correct answer is single circulation. In organisms with a single circulation system, blood flows in a single loop through the body. This means that deoxygenated blood is pumped from the heart to the gills, where it is oxygenated before returning to the heart. After this, it is then pumped directly to the rest of the body to deliver oxygen and nutrients.

This system is typical of many fish and allows for effective oxygenation of blood in the gills before it continues its journey to the tissues. The simplicity of this design is well-suited for aquatic organisms, as gills can extract oxygen efficiently from water.

In contrast, double circulation involves two distinct circuits: one for oxygenating blood in the lungs and another for delivering that oxygenated blood to the rest of the body, which is not applicable here. Circular circulation is not a commonly used term in physiology, and systemic circulation refers specifically to the part of the circulatory system that delivers blood to the body tissues, rather than focusing on the stage before reaching the body post-gills.