Each haemoglobin molecule can carry............... molecules of oxygen, one in each ..............

Explanation

**Step-by-Step Text Solution:**

1. **Understanding Hemoglobin:** Hemoglobin is a respiratory pigment found in red blood cells (erythrocytes) that plays a crucial role in transporting oxygen from the lungs to the body tissues.

2. **Structure of Hemoglobin:** Each hemoglobin molecule is composed of four subunits, which are globular proteins. This structure is essential for its function.

3. **Binding Capacity:** Each of the four subunits in a hemoglobin molecule can bind to one molecule of oxygen (O2). This means that a fully saturated hemoglobin molecule can carry a total of four oxygen molecules.

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