In humans, respiration occurs in the following steps. Arrange these steps in the correct order.
A. Diffusion of O2 and CO2 between blood and tissues
B. Diffusion of O2 and CO2 across alveolar membrane
C. Pulmonary ventilation by which atmospheric air is drawn in and CO2 rich alveolar air is released out
D. Cellular respiration
E. Transport of gases by the blood
Choose the correct answer from the options given below:

The correct sequence for human respiration is C, B, E, A, D.

Step C: Pulmonary ventilation – Air is drawn into the lungs (inspiration) and expelled (expiration). This moves atmospheric air into the alveoli and removes CO₂‑rich alveolar air from the lungs.

Step B: Diffusion of O₂ and CO₂ across the alveolar membrane – Oxygen from the inhaled air diffuses across the thin alveolar–capillary barrier into the blood, while carbon dioxide diffuses in the opposite direction to be exhaled.

Step E: Transport of gases by the blood – Oxygen binds to hemoglobin in red blood cells and is carried via the circulatory system to peripheral tissues; carbon dioxide is carried back to the lungs mainly as bicarbonate ions.

Step A: Diffusion of O₂ and CO₂ between blood and tissues – In the systemic capillaries, oxygen diffuses from the blood into the tissue cells, and carbon dioxide diffuses from the cells into the blood.

Step D: Cellular respiration – Within the cells, oxygen is used in the mitochondria to produce ATP, and carbon dioxide is generated as a metabolic waste product, completing the cycle.