Question

How does the blood absorb oxygen in the lungs?

Answer 1

Hint: Respiration is the process in which the gases such as carbon dioxide and oxygen are exchanged between the blood and external environment. During respiration, the complex substances (such as carbohydrates) are broken down to form simpler substances like water and carbon dioxide. Oxygen is utilized during this process. The synthesis of ATP takes place with the help of energy produced during this process.

Complete answer:
The respiratory system helps in respiration. It involves the exchange of gases between the lungs and body tissues. The alveoli of the lungs are responsible for the exchange of gases between the blood and surroundings. The following steps help the blood to absorb oxygen in the lungs:
When we breathe air, it reaches the alveoli of the lungs to supply oxygen. At the alveolar site, the partial pressure of oxygen is higher than the partial pressure of carbon dioxide. Hence when the impure blood reaches the alveolar capillaries, the oxygen binds with haemoglobin and forms oxyhaemoglobin in the capillary blood.
The oxyhaemoglobin is acidic in nature and thus it helps in the breakdown of sodium bicarbonate ($NaHCO_3$) present in blood. The carbon dioxide is released due to the breakdown of $NaHCO_3$.
Hence due to the high concentration of oxygen at the alveoli, the oxygen leaves the alveolar site and enters the red blood cells and binds with the haemoglobin. After that the pure blood which carries oxygen reaches to all cells and tissues of the body to supply oxygen there for various cellular activities. At the tissue level, the carbon dioxide diffuses into the blood and reaches the alveoli of the lungs from where it is exhaled out (released outside the body) through the nose.

Note:
The partial pressure gradient helps in the movement of gases i.e. from high partial pressure to low partial pressure. In the alveolar site, the gas exchange between the alveoli and the blood capillaries takes place by simple diffusion.