Oxyhaemoglobin is an acidic compound and thus releases H+ ions. Those ions combine with the bicarbonate ions to release the CO2 associated with them. This is known as Haldane effect.

The Haldane effect refers to the phenomenon in which the binding of oxygen to hemoglobin affects the ability of hemoglobin to bind and carry carbon dioxide. It is named after John Scott Haldane, a British physiologist who first described this effect in 1907.

The correct answer to this question is option 'D', CO2. The Haldane effect is mainly due to the influence of oxygen on the binding of carbon dioxide to hemoglobin.

Explanation:

- The Role of Hemoglobin:
Hemoglobin is the protein found in red blood cells that is responsible for transporting oxygen from the lungs to the tissues and carrying carbon dioxide from the tissues back to the lungs. It consists of four subunits, each containing a heme group that can bind to either oxygen or carbon dioxide.

- Oxygen Binding and Haldane Effect:
When oxygen binds to hemoglobin, it alters the conformation of the protein and reduces its ability to bind carbon dioxide. This is known as the Haldane effect. In other words, the presence of oxygen decreases the affinity of hemoglobin for carbon dioxide.

- Oxygenation and CO2 Unloading:
When oxygen binds to hemoglobin in the lungs, it causes a conformational change that allows the release of carbon dioxide. This is essential for efficient gas exchange in the lungs. The binding of oxygen to hemoglobin in the lungs promotes the unloading of carbon dioxide, which can then be expelled from the body.

- Deoxygenation and CO2 Loading:
In the tissues, where oxygen levels are lower, hemoglobin has a higher affinity for carbon dioxide. As hemoglobin releases oxygen to the tissues, it also has a higher capacity to bind carbon dioxide. This allows for the efficient removal of carbon dioxide, which is a waste product of cellular respiration.

- Role of pH:
While pH does influence the oxygenation and deoxygenation of hemoglobin (as seen in the Bohr effect), it is not directly related to the Haldane effect. The Haldane effect primarily describes the influence of oxygen on carbon dioxide binding to hemoglobin.

In summary, the Haldane effect is a phenomenon in which the binding of oxygen to hemoglobin affects the ability of hemoglobin to bind and carry carbon dioxide. This effect is due to the conformational changes in hemoglobin caused by oxygen binding.