Problem 49 - A Complete Resource Book in Chemistry for JEE Main

Question

The protein of the haemoglobin converts \(\mathrm{CO}_{2}\) of the tissues into (a) \(\mathrm{O}_{2}\) and \(\mathrm{C}\) (b) \(\mathrm{HCO}_{3}^{-}\)and \(\mathrm{Fe}^{2+}\) (c) \(\mathrm{O}_{2}\) and \(\mathrm{CO}\) (d) \(\mathrm{HCO}_{3}^{-}\)and \(\mathrm{H}^{+}\)

Step-by-Step Solution

Answer

(d) \(\mathrm{HCO}_{3}^{-}\) and \(\mathrm{H}^{+}\)

Step 1: Understand the Function of Hemoglobin

Hemoglobin is primarily responsible for transporting oxygen from lungs to tissues and carrying carbon dioxide from tissues back to the lungs. It doesn't convert CO2 directly to O2.

Step 2: Carbon Dioxide Transport in Blood

In the blood, carbon dioxide is transported in three ways: dissolved in plasma, chemically combined with hemoglobin, and as bicarbonate ions. The conversion of CO2 into bicarbonate is crucial as it represents the majority of CO2 transport.

Step 3: Conversion Reaction of Carbon Dioxide

When CO2 enters the red blood cells, it reacts with water to form carbonic acid, which then dissociates into bicarbonate (\(\mathrm{HCO}_{3}^{-}\)) and hydrogen ions (\(\mathrm{H}^{+}\)). This reaction is catalyzed by the enzyme carbonic anhydrase.

Step 4: Match the Reaction with the Options

From the conversion reaction, we get \(\mathrm{HCO}_{3}^{-}\)and \(\mathrm{H}^{+}\) as products. The correct option corresponds to these products.

Key Concepts

Carbon Dioxide Transport

Carbon dioxide (CO"") is a waste product formed by cells during metabolism. It needs to be expelled from the body efficiently. In the blood, CO"" is transported in three main ways to facilitate its removal:

• Dissolved in Plasma: A small amount of carbon dioxide dissolves directly in the blood plasma, which is the liquid component of blood.
• Bound to Hemoglobin: Carbon dioxide can bind to hemoglobin to form a compound known as carbaminohemoglobin. This allows hemoglobin to transport CO"" to the lungs for exhalation.
• As Bicarbonate Ions: The majority of CO"" in the blood is transported in the form of bicarbonate ions, a more manageable way to carry CO"" to the lungs.

This multi-faceted transport system ensures that carbon dioxide is efficiently transported from tissues and ultimately eliminated through respiration.

Bicarbonate Ion Formation

When carbon dioxide enters red blood cells, with the help of water, it undergoes a transformation to bicarbonate ions (HCO_{3}^{-}""). This process plays a crucial role in maintaining the acid-base balance in the blood, as bicarbonate acts as a buffer. The steps for bicarbonate ion formation include:

• Firstly, CO"" combines with water inside red blood cells to form carbonic acid (H_{2}CO_{3}"").
• Subsequently, carbonic acid dissociates into bicarbonate ions (HCO_{3}^{-}"") and hydrogen ions (H^{+}"").

Most of the bicarbonate then moves out of the red blood cells into the plasma, where it can be transported through the bloodstream. This mechanism is vital because it helps to convert carbon dioxide, which is less soluble, into bicarbonate, which is more easily transported in the blood.

Carbonic Anhydrase Reaction

The conversion of carbon dioxide and water into carbonic acid is expedited by the enzyme carbonic anhydrase. This enzyme is abundant in red blood cells and ensures that the reaction occurs swiftly to meet the body's needs. Without carbonic anhydrase, the reaction would be too slow to adequately manage carbon dioxide removal. The function of carbonic anhydrase can be described in simple terms:

• Carbonic anhydrase facilitates the quick conversion of carbon dioxide and water into carbonic acid.
• It then aids in the dissociation of carbonic acid into bicarbonate ions and hydrogen ions.
• The rapidity of this reaction ensures effective buffering of blood acidity and efficient gas exchange in the lungs.

By speeding up the conversion, carbonic anhydrase plays an essential role in both maintaining physiological pH levels and supporting the efficient transport of carbon dioxide in the bloodstream.