Answer
b.
Work Step by Step
Humans have a double circulation system. The right side of the heart is involved with the pulmonary circuit where oxygen-poor blood enters the right atria and is pumped by the right ventricle to the lungs to pick up oxygen. The left side of the heart is responsible for the systemic circulation. The left atrium receives oxygen-rich blood from the lungs and sends this blood to the rest of the body.
In a fish heart, there is only one atrium and one ventricle. Blood is pumped by the heart to the gills where oxygen is picked up. The blood then circulates to the organs and tissues. Oxygen-poor blood then returns to the atrium. There is only one circuit in the fish circulatory system.
