Which one of the following statements regarding haemoglobin is correct?

Haemoglobin is the primary respiratory pigment in human red blood cells (RBCs) responsible for the transport of respiratory gases [2]. While it has a very high affinity for oxygen, forming oxyhaemoglobin to deliver oxygen to tissues [2], it also plays a critical role in transporting carbon dioxide. Approximately 23–24% of carbon dioxide binds directly to the amino groups of the haemoglobin molecule to form carbaminohaemoglobin. This complex facilitates the transport of CO2 from the body tissues back to the lungs for elimination [3]. Although a significant portion of CO2 is also transported in dissolved form in plasma or as bicarbonate ions, the ability of haemoglobin to bind both gases is a fundamental physiological function [2]. Therefore, haemoglobin of RBCs can carry both oxygen and carbon dioxide, making option 2 the correct statement.

Sources

1. [2] https://www.ncbi.nlm.nih.gov/books/NBK539815/
2. [3] https://www.sciencedirect.com/topics/biochemistry-genetics-and-molecular-biology/carbaminohemoglobin