$(a)$ Draw a sectional view of the human heart and label on it Aorta,Pulmonary arteries,Vena cava,Left ventricle.
$(b)$ Why is double circulation of blood necessary in human beings?

(N/A) The sectional view of the human heart is shown in the provided figure.
$(b)$ Double circulation of blood is necessary in human beings for the following reasons:
$(i)$ To separate deoxygenated blood from oxygenated blood,preventing their mixing.
$(ii)$ To meet the high energy and oxygen demands of the body,as humans are warm-blooded organisms.
$(iii)$ To maintain a constant body temperature (homeothermy) by ensuring efficient oxygen supply to all tissues.