Question

Describe the evolutionary change in the pattern of heart among the vertebrates.

Answer 1

Hint: The heart is the organ that is present in every vertebrate and helps in the pumping of blood to the whole body.As the level of organisms increases. The heart got modified and the increase in the number of chambers is seen.

Complete answer:
The evolution of the heart which was observed is based on the separation of oxygenated blood from deoxygenated blood which helps in efficient oxygen transport. It all started with fishes, which have the heart like a hollow tube. After evolution, the most evolved heart is divided into the four-chambers as seen in mammals.
-Heart of the Fish: It is seen that Fish has only two chambers in their heart out of which one is an auricle and the other is the ventricle. As you know that in fishes, both the auricle and the ventricle are not divided, only deoxygenated blood passes through it. The process of oxygenation occurs in gills when the deoxygenated blood enters from the ventricle. Heart of the Fish also has additional chambers such as sinus venosus and conus arteriosus.
- Heart of Amphibians: Amphibians, for example, frogs, have three-chambered hearts, which consist of two auricles and one ventricle. The auricle is further divided into a right and a left chamber by an interauricular septum and the ventricle is not divided further. Additional chambers such as sinus venosus and conus arteriosus are also present in the heart of amphibians. The oxygenated blood from the lungs enters the left auricle and at the same time, the deoxygenated blood from the body enters the right auricle. Both these auricles empty into the ventricle, but here the oxygenated and deoxygenated blood gets mixed to some extent.
-Heart of Reptiles: It was seen that the Reptiles have incomplete four-chambered hearts. They have only one accessory chamber present in them which is known as sinus venosus. The reptilian heart also shows mixed-blood circulation.
- Heart of Aves and Mammals: Aves and Mammals have two pairs of chambers that help in separating oxygenated and deoxygenated types of blood. The heart is further divided into four chambers. The upper two chambers of the heart are called atria and the lower two chambers of the heart are known as ventricles. The chambers are separated with the help of a muscular wall that prevents the mixing of the blood rich in oxygen with the blood rich in carbon dioxide i.e prevent mixing of deoxygenated and oxygenated blood.

Hearts of Different Vertebrates
Note: As you know Reptiles have a three-chambered heart that consists of two atria and one partially divided ventricle. The only exception seen in the reptiles is the crocodile. The crocodile has a four-chambered heart which is similar to the heart of mammals and birds where the ventricles are split completely.