Carbon dioxide is considered a harmful by-product of cellular respiration because it

Options

A. lowers the hydrogen ion concentration in the blood
B. combines with haemoglobin to form carboxyhaemoglobin
C. has more affinity for haemoglobin
D. lowers the pH of the blood

Answer

**Step-by-Step Solution:**

1. **Understanding Cellular Respiration**: Cellular respiration is a metabolic process where cells convert glucose and oxygen into energy, producing carbon dioxide (CO2) and water as by-products.

2. **Identifying the By-Products**: During this process, CO2 is produced as a waste product. While it is a natural part of metabolism, its accumulation can be harmful.

3. **Analyzing the Effects of CO2**:
- CO2 can bind with hemoglobin in red blood cells to form carbaminohemoglobin (HbCO2), but this is not the primary reason it is considered harmful.
- More importantly, CO2 reacts with water in the blood to form carbonic acid (H2CO3), which dissociates into bicarbonate (HCO3-) and hydrogen ions (H+).

4. **Impact on Blood pH**: The increase in hydrogen ions (H+) lowers the pH of the blood, making it more acidic. This change in pH can disrupt various physiological processes and is a key reason why CO2 is considered harmful.

5. **Conclusion**: Among the given options, the correct explanation for why CO2 is considered a harmful by-product of cellular respiration is that it lowers the pH of the blood.

**Final Answer**: Carbon dioxide is considered a harmful by-product of cellular respiration because it lowers the pH of the blood.

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