The most important physioloical feature of haemoglobin is

Options

A. its red colour
B. presence of iron
C. presence of basic protein globi
D. its ability to combine reversibly with oxygen

Answer

### Step-by-Step Text Solution:

1. **Understanding Hemoglobin**: Hemoglobin is a protein found in red blood cells that is crucial for transporting oxygen throughout the body.

2. **Oxygen Transport**: The primary function of hemoglobin is to carry oxygen. It can bind to oxygen molecules, with each hemoglobin molecule capable of binding up to four oxygen molecules due to the presence of iron ions (Fe²⁺).

3. **Reversibility of Binding**: The binding of oxygen to hemoglobin is a reversible reaction. This means that hemoglobin can pick up oxygen in the lungs and release it in tissues where it is needed.

4. **Composition of Hemoglobin**: Hemoglobin is composed of four heme groups (which contain iron) and a globin protein. While the presence of iron and the color of red blood cells are notable features, they are not the most critical physiological feature.

5. **Identifying the Key Feature**: The most important physiological feature of hemoglobin is its ability to combine reversibly with oxygen. This property allows hemoglobin to effectively transport oxygen from the lungs to the tissues and return carbon dioxide from the tissues back to the lungs.

### Conclusion:
The most important physiological feature of hemoglobin is its ability to combine reversibly with oxygen.

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