Question

Assertion- Double circulation is incomplete in amphibians and reptiles.
Reason- Unlike in birds and mammals, in amphibians and reptiles, the left atrium receives oxygenated blood and the right atrium receives deoxygenated blood.
(a)Both Assertion and Reason are correct and Reason is the correct explanation for Assertion.
(b)Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion.
(c)Assertion is correct but the reason is incorrect.
(d)Both Assertion and Reason are incorrect.

Answer 1

Hint: In most amphibians, the cardiovascular system is employed to move blood through the body. In these organisms, blood comes from two different routes and gets mixed in a single chamber.

Complete answer:
All Amphibians and reptiles (except the crocodiles) have a 3-chambered heart. It includes two atria and one ventricle, whereas crocodiles, birds, and mammals possess a 4-chambered heart which includes two atria and two ventricles.
In amphibians and reptiles, the left atrium of the heart receives oxygenated blood from the gills/lungs/skin and therefore the right atrium of the heart gets the deoxygenated blood from other body parts. However, they get involved within the single ventricle which radiates mixed blood (incomplete double circulation). That is why the Double circulation is incomplete in amphibians and reptiles.
In birds and mammals, oxygenated and deoxygenated blood received by the left and right atria respectively passes on to the ventricles of an equivalent side. The ventricles press it out with no mess up, i.e., two separate circulatory pathways are present in these organisms, hence, these animals have double circulation. Here the given reason is incorrect.
So, the correct answer is 'Assertion is correct but Reason is incorrect'

Note: Circulatory systems may be open (mixed with the interstitial fluid) or closed (separated from the interstitial fluid). Closed circulatory systems are characteristic of vertebrates. Fish have a two-chambered heart with unidirectional circulation.