CBSE Class 10 Science 2020 · Paper 31/2/2 · Question 28

(a) Fishes have a two-chambered heart (one atrium and one ventricle), while human beings have a four-chambered heart (two atria and two ventricles). In fishes the heart pumps deoxygenated blood to the gills, where it is oxygenated, and the blood then passes directly to the body, so it goes through the heart only once in each round: single circulation. In human beings blood goes through the heart twice in each round, once on its way to the lungs and once on its way to the body: double circulation, which keeps oxygenated and deoxygenated blood separate. (b) Deoxygenated blood from all parts of the body is collected by the veins into the vena cava, which pours it into the right atrium. The right atrium passes it to the right ventricle, which pumps it through the pulmonary artery to the lungs. In the lungs the blood gives out carbon dioxide and takes up oxygen. The oxygenated blood returns through the pulmonary vein to the left atrium, which passes it to the left ventricle. The left ventricle pumps it into the aorta, which distributes it through arteries to all parts of the body.