**Question:** Which of the following is not true about buffering action of haemoglobin (Hb)?

A. Haemoglobin plays a role in the buffering of blood pH during respiration
B. The primary role of haemoglobin is to transport oxygen
C. The capacity of haemoglobin to buffer blood pH decreases with increasing oxygen saturation
D. The buffering action of haemoglobin is independent of oxygen binding

**Correct Answer: D. The buffering action of haemoglobin is independent of oxygen binding**

**Core Concept:**
The buffering action of haemoglobin (Hb) is a crucial mechanism in maintaining blood pH balance, particularly during respiration when oxygen and carbon dioxide levels fluctuate. Haemoglobin is a protein found in red blood cells, responsible for transporting oxygen from the lungs to the tissues and back to the lungs. Oxygen binds to haemoglobin in the lungs and unbinds in the tissues, and vice versa.

**Why the Correct Answer is Right:**
The primary role of haemoglobin is to transport oxygen, as stated in option B. However, haemoglobin also possesses a buffering action, which is an essential function in maintaining blood pH homeostasis. This buffering action is important during respiration, as the respiratory process leads to fluctuations in blood pH due to the production of carbon dioxide (CO2) and its elimination.

**Why Each Wrong Option is Incorrect:**
Option A and C are correct, as haemoglobin plays a role in buffering blood pH and this capacity does change with oxygen saturation. As oxygen saturation increases, the capacity to buffer blood pH decreases, as mentioned in option C.

Option B is incorrect as the buffering action of haemoglobin is not independent of oxygen binding. Oxygen binding to haemoglobin significantly affects its buffering capacity, which is why option C is correct.

Option D is incorrect because the buffering action of haemoglobin is not independent of oxygen binding. The buffering capacity of haemoglobin changes according to its oxygen saturation, which is contrary to the statement in option D.

**Clinical Pearl:**
Understanding the relationship between oxygen binding to haemoglobin and its buffering capacity is crucial for medical professionals as it directly affects the ability of the blood to maintain blood pH homeostasis, particularly during respiratory processes. This knowledge helps in interpreting blood gas analysis and making accurate clinical decisions regarding respiratory management, especially in patients with respiratory distress or acid-base imbalances.