External Respiration: Definition and Explanation

External respiration refers to the exchange of gases (oxygen and carbon dioxide) between the air in the lungs and the blood in the pulmonary capillaries. It involves several steps, including ventilation, diffusion, and transport.

Ventilation: The process of breathing, which involves the movement of air in and out of the lungs.

Diffusion: The movement of gases from an area of high concentration to an area of low concentration. In external respiration, oxygen diffuses from the air in the lungs into the blood in the pulmonary capillaries, while carbon dioxide diffuses from the blood into the air.

Transport: The movement of gases in the blood, which involves binding to hemoglobin (in the case of oxygen) or being carried as bicarbonate ions (in the case of carbon dioxide).

Which Reaction is Part of External Respiration?

The correct answer is option A: O2 + Hb = HbO2.

This reaction represents the binding of oxygen (O2) to hemoglobin (Hb) to form oxyhemoglobin (HbO2). This is a crucial step in external respiration, as it allows for the transport of oxygen from the lungs to the tissues.

Option B (CO2 + Hb = HbCO2) represents the binding of carbon dioxide (CO2) to hemoglobin to form carbaminohemoglobin. While this reaction does occur in the blood, it is not considered a part of external respiration.

Option C (O2 + H2O = H2O2) is not a reaction that occurs in the body.

Option D (CO2 + H2O = H2CO3) represents the formation of carbonic acid (H2CO3) from carbon dioxide and water. While this reaction does occur in the blood, it is not considered a part of external respiration.