CBSE Class 9 Answered

Birds and mammals are warm-blooded animals and maintain a constant body temperature by cooling themselves when they are in a hotter environment and vice versa. So, for respiration to carry out, more eoxygen is required. So, an efficient system of heart is required to separate the oxygenated and deoxygenated blood to carry out proper functioning of the circulatory system which in turn is linked to respiratory system too. So, the four chambered heart is an efficient design that allows to send "dirty" blood to the the lungs-and "clean" blood to the rest of the body without having to mix the two.