Problem 88 - Objective Biology for NEET

Question

Oxygen binding to haemoglobin is (a) Directly proportional to \(\mathrm{CO}_{2}\) concentration (b) Directly proportional to CO concentration (c) Inversely proportional to \(\mathrm{CO}_{2}\) concentration (d) Independent of CO concentration

Step-by-Step Solution

Answer

(b) Directly proportional to CO concentration and (c) Inversely proportional to \( \mathrm{CO}_{2} \) concentration

Step 1: Understanding Hemoglobin Binding

First, it's important to understand how hemoglobin works. Hemoglobin binds to oxygen in the lungs and carries it to the parts of the body where it's needed. The ability of hemoglobin to pick up or release oxygen is influenced by certain factors.

Step 2: Effects of CO2 Concentration

The relationship between hemoglobin and carbon dioxide concentration is that the binding capacity of hemoglobin for oxygen decreases with increasing \( \mathrm{CO}_{2} \) concentration. This is due to the Bohr effect: as carbon dioxide increases, the blood becomes more acidic, which promotes the release of oxygen. Therefore, oxygen binding to hemoglobin is inversely proportional to \( \mathrm{CO}_{2} \) concentration, making the option (c) correct.

Step 3: Effects of CO Concentration

Carbon monoxide competes with oxygen for the binding sites on hemoglobin. It binds to hemoglobin at the same site as oxygen with an affinity about 200 times greater. When CO is present, it decreases the amount of hemoglobin available for oxygen binding. This means CO concentration directly impacts the amount of oxygen hemoglobin can carry, making the option (b) correct. Note that, despite being able to bind to hemoglobin, CO does not provide the oxygen necessary for bodily functions.

Key Concepts

Bohr Effect

The Bohr Effect is a physiological phenomenon where the binding affinity of hemoglobin for oxygen decreases as the concentration of carbon dioxide in the blood increases. This effect is crucial for the efficient delivery of oxygen to tissues that need it the most. Here's how it works:

• More carbon dioxide in the blood leads to the formation of carbonic acid, lowering the pH.
• The lowered pH changes the shape of hemoglobin, reducing its affinity for oxygen.
• This facilitates the release of oxygen in tissues where carbon dioxide concentration is high, such as working muscles or active organs.

In essence, the Bohr Effect ensures that as cells produce more carbon dioxide through metabolism, they receive more oxygen, providing an elegant feedback mechanism that matches oxygen delivery with tissue demand.

Carbon Dioxide Concentration

Carbon dioxide concentration is a key factor influencing the ability of hemoglobin to bind oxygen. As carbon dioxide levels rise in the blood, the following occurs:

• Carbon dioxide diffuses into red blood cells, reacting with water to form carbonic acid, which dissociates into bicarbonate ions and hydrogen ions.
• The increase in hydrogen ions leads to a decrease in blood pH, creating acidic conditions.
• These acidic conditions cause hemoglobin to release its bound oxygen more readily, a direct application of the Bohr Effect.

Understanding this interaction helps explain why hemoglobin's oxygen-binding capacity is inversely proportional to carbon dioxide concentration. In simpler terms, more carbon dioxide in the blood means less oxygen is bound to hemoglobin.

Carbon Monoxide Competition

Carbon monoxide (CO) is a dangerous gas because it competes directly with oxygen for binding to hemoglobin. Here's why CO affects oxygen transport:

• Hemoglobin binds carbon monoxide with much higher affinity (approximately 200 times greater) than it does oxygen.
• When carbon monoxide is inhaled, it quickly occupies the oxygen binding sites on hemoglobin molecules.
• This prevents oxygen from binding, reducing the amount of oxygen that can be transported in the bloodstream.

Even though carbon monoxide binds effectively to hemoglobin, it does not help in oxygen transport. This competition makes carbon monoxide extremely hazardous, as it can lead to oxygen deprivation in tissues, despite stable levels of oxygen in the air. Understanding this concept highlights the critical need for effective carbon monoxide detectors in environments where CO exposure might occur.