Question

During respiration, exchange of gases take place in

• A. Trachea and larynx
• B. Alveoli of lungs
• C. Alveoli and throat
• D. Throat and larynx

Answer 1

The correct option is B Alveoli of lungs

Hint: Respiration is the biochemical process that involves the production of energy by combining oxygen and glucose, resulting in the release of carbon dioxide, water, and ATP (energy). Breathing is just a part of respiration that involves the exchange of respiratory gases with the external environment.

Part 1 - Breathing or external respiration

• External respiration, also known as breathing, involves both bringing air into the lungs (inhalation) and releasing air to the atmosphere (exhalation).
• To forces, the air to move from outside into the lungs, the pressure in the lungs needs to be lower than the atmospheric pressure.
• The contraction of the diaphragm increases the volume of the thoracic chamber in the front and back.
• This volume is further increased by the contraction of external intercostal muscles, which lift up the ribs and sternum.
• While during exhalation, the diaphragm and the intercostal muscles relax, the ribs and sternum return to their normal positions.

Part 2 - Process of Gaseous exchange within Alveoli

• There are millions of alveoli within each lung that serves as the actual site of gaseous exchange.
• There is an extensive network of blood capillaries and blood vessels here.
• As the air enters our lungs through the nasal passage, the alveoli get filled with air.
• The oxygen is taken in by the blood vessels in the alveoli through simple diffusion.
• The partial pressure of oxygen is higher in the alveoli (104 mm Hg) compared to deoxygenated blood (40 mm Hg), which facilitates the diffusion of oxygen from the alveoli to the blood.
  
• Similarly, the partial pressure of carbon dioxide in alveoli (40 mm Hg) is less compared to the blood coming from tissues (45 mm Hg), which facilitates the release of CO2 in alveoli.
  

Part 3 - Conclusion

• From the above discussion, we can conclude that simple diffusion between the alveoli and blood in the lung is the result of differences in partial pressure of respiratory gases ( $O_2$ and $C{O}_2$). That difference brings the gaseous exchange between alveoli and blood vessels surrounding them.

Final step: During respiration, the exchange of gases takes place in the alveoli of lungs