Why amphibians and reptiles have complete and incomplete blood Circulatory ststem while in chordates one time and two time blood touch to the heart???
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Answer:
Circulatory system
Modern reptiles do not have the capacity for the rapid sustained activity found in birds and mammals. It is generally accepted that this lower capacity is related to differences in the circulatory and respiratory systems. Before the origin of lungs, the vertebrate circulatory system had a single circuit: in the fishes, blood flows from heart to gills to body and back to the heart. The heart consists of four chambers arranged in a linear sequence.
Types of reptilian hearts: lizard, snake, crocodile, and turtle.
Types of reptilian hearts: lizard, snake, crocodile, and turtle.
Encyclopædia Britannica, Inc.
With the evolution of lungs in early tetrapods, a new and apparently more efficient circulatory system evolved. Two chambers of the heart, the atrium (or auricle) and ventricle, became increasingly important, and the beginnings of double circulation appeared. An early stage in this evolution can be seen in amphibians today, where one of the main arteries from the heart (the pulmonary artery) goes directly to the lungs, whereas the others (the systemic arteries) carry blood to the general body. In amphibians the blood is aerated in the lungs and carried back to the atrium of the heart. From the left side of the atrium, which is at least partially divided, the aerated blood is pumped into the ventricle to mix with nonaerated blood; nonaerated blood from the body is returned to the heart via the right half of the atrium. Then the cycle begins again. One aspect of the amphibian system is that the blood leaving the heart for the body is only partially aerated; part of it is made up of deoxygenated blood returned from the body.