Understanding the Role of Haemoglobin in Gas Transport

Haemoglobin is a vital protein found in Red Blood Cells (RBCs). Its primary function is to transport gases throughout the body, enabling respiration.

Let's examine how haemoglobin interacts with the key respiratory gases, oxygen and carbon dioxide.

Haemoglobin and Oxygen Transport

• Haemoglobin has a high affinity for oxygen.
• In the lungs, where oxygen concentration is high, oxygen binds to the haemoglobin molecule.
• This binding forms a molecule called oxyhaemoglobin.
• This is the main way oxygen is transported from the lungs to the body's tissues.

Haemoglobin and Carbon Dioxide Transport

• Haemoglobin also plays a role in transporting carbon dioxide, although it is not the primary method for all CO2 transport.
• About 20-25% of the carbon dioxide transported in the blood binds directly to the amino groups of the haemoglobin molecule.
• This forms a compound known as carbaminohemoglobin.
• The majority of carbon dioxide is transported in the blood plasma as bicarbonate ions, a process that also relies on an enzyme (carbonic anhydrase) present in RBCs, but the direct binding to haemoglobin is significant.

Analyzing the Options

Now let's evaluate the given statements regarding haemoglobin and its gas-carrying capacity:

• Option 1: Haemoglobin present in RBC can carry only oxygen but not carbon dioxide. This is incorrect because haemoglobin does bind with carbon dioxide to form carbaminohemoglobin.
• Option 2: Haemoglobin of RBC can carry both oxygen and carbon dioxide. This statement is correct. Haemoglobin binds significantly with oxygen and also binds with a portion of carbon dioxide.
• Option 3: Haemoglobin of RBC can carry only carbon dioxide. This is incorrect. While it carries carbon dioxide, its primary role and much higher affinity is for oxygen transport.
• Option 4: Haemoglobin is only used for blood clotting and not for carrying gases. This is incorrect. Haemoglobin's main function is gas transport (oxygen and carbon dioxide). Blood clotting is primarily handled by platelets and clotting factors, not haemoglobin.

Based on the functions of haemoglobin, the correct statement is that it can carry both oxygen and carbon dioxide.

Revision Table: Haemoglobin Transport

Additional Information: Carbon Dioxide Transport in Blood

While haemoglobin carries some carbon dioxide directly, the majority of CO\(_{2}\) is transported in other forms:

• Bicarbonate Ions: Around 70% of CO\(_{2}\) is converted into bicarbonate ions (HCO\(_{3}^{-}\)) within RBCs, facilitated by the enzyme carbonic anhydrase. These ions then move into the plasma.
• Dissolved CO\(_{2}\): A small amount (about 7-10%) of CO\(_{2}\) is transported simply dissolved in the blood plasma.

Understanding these different mechanisms provides a complete picture of carbon dioxide transport alongside oxygen transport by haemoglobin.