Oxygen transportation in a human body takes place through I. Blood II. Lungs III. Tissue The correct sequence of transportation is

Oxygen uptake and delivery follow the pathway lungs → blood → tissues (II, I, III). In the lungs, air fills the alveoli and oxygen diffuses across the thin alveolar-capillary membrane into pulmonary blood, allowing gas equilibration between alveoli and capillaries [1]. Once in the circulation, most oxygen is bound to haemoglobin inside red blood cells and carried by the blood throughout the body [3]. The heart and vessels then pump this oxygenated blood to systemic capillaries, where oxygen dissociates from haemoglobin and diffuses into oxygen-deficient tissues for cellular respiration [2]. Therefore the correct sequence is II (lungs), I (blood), III (tissues), i.e., option 3.

Sources

1. [1] Science-Class VII . NCERT(Revised ed 2025) > Chapter 9: Life Processes in Animals > How does the exchange of gases happen? > p. 132
2. [2] Science , class X (NCERT 2025 ed.) > Chapter 5: Life Processes > Do You Know? > p. 90
3. [3] Science , class X (NCERT 2025 ed.) > Chapter 5: Life Processes > Activity 5.7 > p. 91