CBSE Class 10 Science 2023 · Paper 31/C/2 · Question 29

Air breathed in reaches the alveoli of the lungs, whose thin walls are surrounded by a dense network of blood capillaries. Oxygen diffuses from the air in the alveoli into the blood, where it combines with haemoglobin, the respiratory pigment in the red blood cells, which has a very high affinity for oxygen. The oxygen-rich blood is carried by the pulmonary veins to the left atrium, passes into the left ventricle and is pumped through the aorta and the arteries to the capillaries throughout the body. There, where the oxygen concentration is low, oxygen is released from haemoglobin and diffuses into the cells. Carbon dioxide is more soluble in water than oxygen is, so it is mostly transported in the dissolved form, in the plasma of the blood.