Question

Majorly the heart is four chambered in
A. Amphibia
B. Fishes
C. Mammals
D. Reptiles

Answer 1

The four chambered heart is the characteristic which is present in higher organisms of class vertebrata. The development to four chambered hearts include two atrium and two ventricles which function in coordinated manner to pump the blood to the body.

Complete step by step answer: Now we will discuss the heart structures of the options given and number of chambers present in them:
Amphibia: The heart structure of an amphibian is three chambers having two atrium and one ventricle. The atrium functions in receiving the blood from lungs and the other body systems of amphibians.
Fishes: the heart of fish has only one ventricle and one atrium. The deoxygenated blood from the body enters the atrium and then passes on to ventricles and when the blood is passed through the gill slits gets oxygenated and then is supplied to the rest of the body.
Mammals: mammalian heart is four chambered heart where there is occurrence of the double circulation which is passage of the blood through the heart twice during one complete cardiac cycle. Two atriums and two ventricles work in a coordinated way, atrium receives the deoxygenated blood and ventricles pass on the oxygenated blood to the body after oxygenation of the blood from the lungs.
Reptiles: Reptilian heart is a three chambered heart with the exception of crocodile which has four chambered. There is presence of two atrium and one ventricle and the deoxygenated blood is received by atrium of the heart.
Thus the correct option is C, i.e. mammals.

Note: : If we follow up the development from 2 chambered heart to three chambered heart to four chambered heart, it proves that the evolution of all vertebrates is from common fish like ancestors and the evolution of birds and mammals is from reptiles.