Question

In which of the following groups of animals, the heart pumps only deoxygenated blood?
a. Fishes
b. Reptile
c. Birds
d. Amphibians

Answer 1

Hint: The groups of the animals in which the heart pump only deoxygenated blood belongs to phylum Chordata and subphylum Vertebrata. These animals have a two-chambered heart. The blood flows in one circuit from the heart to the organs and tissue for the gaseous exchange and back to the heart.

Complete answer:
• Fishes have a single circuit of blood circulation. They contain a two-chambered heart having one auricle and one ventricle. It contains and pumps only deoxygenated blood hence called branchial heart or venous.
• They have sinus venosus, a thin-walled sac in which the blood from fish veins collects and then it flows to the atrium, a large muscular chamber. Then the atrium sends the blood to the ventricle, also a thick-walled muscular sac. The ventricle further sends the blood to the bulbus arteriosus, a large tube, and then out of the heart.
• Through the bulbus arteriosus, the blood flows to the gills for oxygenation as it is connected to the aorta.

Also,
The amphibians and reptiles have a three-chambered heart (two auricles and one ventricle). Birds have a completely four-chambered heart (two auricles and two ventricles) where double circulation takes place.

Hence, the correct answer is option (A).

Note: So, fishes have only two-chambered hearts containing one auricle and one ventricle. The heart pumps only deoxygenated blood (absence of dissolved oxygen) so it is called the venous heart. The blood goes to the gills (an organ for gaseous exchange) for the process of oxygenation.