Question

Which of the following groups of animals the heart pumps only deoxygenated blood?
(a)Fishes
(b)Birds
(c)Reptiles
(d)All of the above

Answer 1

Hint: The heart pump only deoxygenated blood because the heart is two-chambered with an atrium and a ventricle. The heart pumps out deoxygenated blood which is oxygenated by the gills and supplied to other body parts from where deoxygenated blood is returned to the heart.

complete answer:
-Fishes have a single systemic circuit for blood. In this system, the heart pumps the blood to the gills to be re-oxygenated ( gill circulation).
-Later the blood flows to the rest of the body and back to the heart.
-Fishes have a closed-loop circulatory system.
-They have single cycle circulation.
-Amphibians have a three-chambered heart and mixed circulation.
-In amphibians, reptiles, birds, and mammals, both pulmonary well as systemic circulation is present.

Additional information:
-Birds and mammals possess a four-chambered heart. Oxygenated and deoxygenated blood are well separated.
-In reptiles, the circulatory system consists of a three-chambered heart with two atria and one partially divided ventricle. So there is little mixing of both deoxygenated and oxygenated blood.
-In amphibians, there are two pathways. The first pathway is for oxygenation of blood through lungs and skin and another one is to carry oxygen to all other body parts.

So the correct answer is ‘Fishes’.

Note: Different blood types exist in fish just as in humans, although the types are not the same. The fish heart has to generate the driving pressure for both the gills and the body since they are connected in series. The two-chambered heart is the most primitive type of heart system present. It has only one auricle and one ventricle present. The auricle takes in the blood from the gills of the fish which is oxygen-rich in nature and then pumps to the ventricle which then pumps to the rest of the body parts so that they can receive oxygen-rich blood.