Question

In which of the following vertebrate group/groups, the heart does not pump oxygenated blood to different parts of the body?
A. Pisces and amphibians
B. Amphibians and reptiles
C. Amphibians only
D. Pisces only

Answer 1

Hint: Pisces (fish) have the simplest circulatory systems among the vertebrates. In fishes, blood flows in one direction that is from the two-chambered heart through the gills and then to the rest of the body.

Complete answer:
The class Pisces of the phylum Vertebrata includes fish and have an only single circuit of blood flow. The fish heart consists of a two-chambered heart with one auricle and one ventricle. The atrium collects deoxygenated blood which returns from the body cells through sinus venosus and the ventricle, a thick-walled chamber pumps the deoxygenated blood to the gills. Gills the site where gaseous exchange occurs and the blood is oxygenated with the water dissolved oxygen. The oxygenated blood then continues to the rest of the body cells before arriving back at the atrium. Thus, in fish only the type of circulation occurs, that is the systemic circulation. The unidirectional flow of blood produces a gradient of oxygenated to deoxygenated blood around the fish single circuit. In this type of circulation, a limited amount of oxygen reaches to some of the organs and tissues of the body. This reduces the overall metabolic capacity of fish.

Thus, option D. Pisces only is the correct answer.

Note:
In Pisces, the heart does not pump oxygenated blood to different parts of the body. This is because Pisces have a two-chambered heart. Since both the auricle and ventricle remain undivided, only deoxygenated blood passes through it. The deoxygenated blood then enters the gills for oxygenation from the ventricle.