The pH value of blood does not change appreciably by a small addition of an acid or base, because the blood

Options

A. is a body fluid
B. can be easily coagulated
C. contains iron as a part of the molecule
D. contains serum protein that acts as buffer

Explanation

**Step-by-Step Solution:**

1. **Understanding the Concept of pH and Buffers:**
- The pH scale measures the acidity or basicity of a solution. A pH of 7 is neutral, below 7 is acidic, and above 7 is basic.
- Blood has a normal pH range of about 7.35 to 7.45. It is crucial for physiological functions to maintain this pH range.

2. **Identifying the Role of Buffers:**
- A buffer solution is a system that resists changes in pH upon the addition of small amounts of acids or bases.
- Buffers typically consist of a weak acid and its conjugate base or a weak base and its conjugate acid.

3. **Recognizing Blood as a Buffer System:**
- Blood contains buffer systems that help maintain its pH. One of the primary buffer systems in blood is the bicarbonate buffer system.
- The bicarbonate buffer system consists of carbonic acid (H2CO3) and sodium bicarbonate (NaHCO3).

4. **Chemical Reaction in the Buffer System:**
- When an acid (H+) is added to the blood, it can react with bicarbonate (HCO3-) to form carbonic acid (H2CO3), which minimizes the change in pH.
- Conversely, if a base (OH-) is added, it can react with carbonic acid (H2CO3) to form bicarbonate (HCO3-) and water, again minimizing the change in pH.

5. **Conclusion:**
- Therefore, the reason the pH value of blood does not change appreciably with the addition of small amounts of acid or base is that blood contains buffer systems, specifically the carbonic acid and sodium bicarbonate system, which effectively neutralizes the added acids or bases.

**Final Answer:**
The pH value of blood does not change appreciably by a small addition of an acid or base because blood contains buffer systems, primarily the carbonic acid (H2CO3) and sodium bicarbonate (NaHCO3), which resist changes in pH.

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