UPSC CSE Prelims 1997
The correct sequence of transportation is
The correct sequence for oxygen transportation in the human body is Lungs → Blood → Tissues. Oxygen is initially inhaled into the lungs, where it diffuses from the alveoli into the pulmonary capillaries. Within the bloodstream, oxygen primarily binds to hemoglobin in red blood cells, forming oxyhemoglobin. This oxygenated blood is then circulated by the heart to various body tissues. At the tissue level, oxygen dissociates from hemoglobin and diffuses into the cells to support cellular respiration and metabolic activities.
Option (a) 1, 2, 3 (Blood, Lungs, Tissue): This sequence is incorrect because oxygen is absorbed into the blood from the lungs, not received by blood before reaching the lungs.
Option (b) 3, 1, 2 (Tissue, Blood, Lungs): This sequence represents a reversal of the physiological process. Oxygen is delivered to tissues from the blood, and the blood receives oxygen from the lungs, not the other way around.
Option (d) 1, 3, 2 (Blood, Tissue, Lungs): This sequence is incorrect as it misrepresents the origin and destination of oxygen. Oxygen originates in the lungs, is transported by the blood, and then delivered to the tissues. It does not flow from blood to tissue and then back to lungs in this context of systemic oxygen delivery.