Select the favourable conditions required for the formation of oxyhaemoglobin at the alveoli.

High pO2, low pCO2, less H+, lower temperature

Low pO2, low pCO2, more H+, higher temperature

Low pO2, high pCO2, more H+, higher temperature

High pO2, high pCO2, less H+, higher temperature

Identify the WRONG statement with reference to transport of oxygen.

Higher H+ conc. In alveoli favours the formation of oxyhaemoglobin.

Partial pressure of CO2 can interfere with O2 binding with haemoglobin.

Low pCO2 in alveoli favours the formation of oxyhaemoglobin.

Binding of oxygen with haemoglobin is mainly related to partial pressure of O2.

Oxygen Dissociation Curve

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NCERT Class 11 · Breathing and Exchange of Gases · 3 NEET questions

Do not mistake the Oxygen Dissociation Curve for a simple graph. It is the physiological boundary between life and hypoxia. If your haemoglobin doesn't shift its affinity based on pCO2, your tissues die. Understand the sigmoid shape, or lose marks on the most predictable question in the paper.

The idea

The Oxygen Dissociation Curve is a sigmoid plot of percentage saturation of haemoglobin with O2 against partial pressure of oxygen (pO2). This curve demonstrates how haemoglobin's affinity for oxygen changes under varying conditions. Factors like high pCO2, high H+ concentration, and increased temperature shift the curve to the right. This shift facilitates the dissociation of oxygen from oxyhaemoglobin at the tissue level.

Why it matters

The sigmoidal shape reflects the cooperative binding of oxygen to haemoglobin, allowing efficient loading in lungs and unloading in tissues.

NEET lens

NEET focuses on the 'Right Shift' factors: high pCO2, high H+, high temperature, and low pH. Memorize these four triggers as they are frequently tested in match-the-following and statement-based questions. Do not confuse the sigmoid shape with linear graphs; the cooperativity of haemoglobin is the reason for this shape. Expect at least one question on the Bohr effect shift.

Clinical significance

In Carbon Monoxide (CO) poisoning, the curve shifts drastically to the left. CO binds to haemoglobin with 200 times more affinity than O2, preventing oxygen release to tissues. This leads to cellular asphyxiation even when blood oxygen levels appear normal on a pulse oximeter.

Introduction

The oxygen-hemoglobin dissociation curve (ODC) shows the relationship between partial pressure of O₂ (pO₂) and hemoglobin saturation (% hemoglobin bound to O₂). It is sigmoid (S-shaped) due to cooperative binding.

Core concept

Curve shape: Sigmoid (S-shaped) due to cooperativity — binding of O₂ to one subunit increases affinity of remaining subunits. Left shift (increased O₂ affinity → O₂ held more tightly): low temperature, low CO₂, high pH (alkalosis), low 2,3-BPG. Right shift (decreased O₂ affinity → O₂ released more readily): high temperature, high CO₂ (Bohr effect), low pH (acidosis), high 2,3-BPG. This ensures: high loading in lungs (high pO₂, low CO₂, low temp) and unloading in tissues (low pO₂, high CO₂, high temp).

Go deeper

Bohr effect: CO₂ and H⁺ decrease hemoglobin's O₂ affinity. In exercising muscles: CO₂ + H₂O → H₂CO₃ → H⁺ + HCO₃⁻. H⁺ binds Hb → conformational change → reduced O₂ affinity → more O₂ released to working muscles. Elegant physiological mechanism.

From Class 10

Hemoglobin carries oxygen from the lungs to tissues. How easily it loads and unloads oxygen depends on the oxygen concentration — this relationship is the oxygen dissociation curve.