Question

In which of the following vertebrate group/groups, oxygenated blood is not pumped by the heart to different parts of the body?

• A. Pisces and amphibians
• B. Amphibians and reptiles
• C. Amphibians only
• D. Pisces only

Answer 1

Answer: (D)

Pisces only

Fishes have closed but a single circulatory system. In a closed circulatory system, blood is contained inside blood vessels and circulates unidirectionally from the heart around the systemic circulatory route, then returns to the heart again. Fish have a single circuit for blood flow and a two-chambered heart that has only a single atrium and a single ventricle. The atrium collects blood that has returned from the body and the ventricle pumps the blood to the gills where gas exchange occurs and the blood is re-oxygenated; this is called gill circulation. The blood then continues through the rest of the body before arriving back at the atrium; this is called systemic circulation. This unidirectional flow of blood produces a gradient of oxygenated to deoxygenated blood around the fish's systemic circuit. The result is a limit on the amount of oxygen that can reach some of the organs and tissues of the body, reducing the overall metabolic capacity of fish.Fishes have two-chambered heart and heart pumps blood to gills for oxygenation. It enters the atrium via the sinus venosus, which contains the pacemaker cells that initiate the contractions. The blood is pumped into the ventricle by the atrium, which is a thin-walled muscular chamber. Then the blood is pumped out into the bulbous arteriosus by the ventricle to the gills for oxygenation. So, the correct answer is option D.