Which factor in tissues favours the formation of
`HCO_(3)^(-)` and `H^(+)` ions in the blood?

Options

A. Low `pCO_(2)`
B. High `pO_(2)`
C. High `pCO_(2)`
D. High alkalinity

Answer

To determine which factor in tissues favors the formation of HCO3^- and H^+ ions in the blood, we can analyze the physiological processes involved in gas exchange and the role of carbon dioxide (CO2) in this context.

### Step-by-Step Solution:

1. **Understanding the Role of CO2**:
- In tissues, cells produce CO2 as a byproduct of cellular respiration. This CO2 diffuses into the blood.

**Hint**: Remember that CO2 is a product of metabolism in tissues.

2. **Formation of HCO3^- and H^+ Ions**:
- When CO2 enters the blood, it reacts with water (H2O) to form carbonic acid (H2CO3), which quickly dissociates into bicarbonate ions (HCO3^-) and hydrogen ions (H^+):
\[ CO2 + H2O \rightleftharpoons H2CO3 \rightleftharpoons HCO3^- + H^+ \]

**Hint**: Look for the chemical reactions that involve CO2 in the blood.

3. **Effect of pCO2 on pH**:
- An increase in the partial pressure of carbon dioxide (pCO2) in the blood leads to a decrease in pH (more acidic conditions). This is due to the increased concentration of H^+ ions.

**Hint**: Consider how changes in CO2 levels affect acidity.

4. **Bohar Effect**:
- The Bohr effect describes how increased CO2 concentration (high pCO2) in tissues promotes oxygen unloading from hemoglobin. This is because high levels of H^+ (low pH) facilitate the release of oxygen.

**Hint**: Recall the relationship between CO2 levels and oxygen transport.

5. **Identifying the Correct Factor**:
- Among the options provided:
- Low pCO2 would not favor the formation of HCO3^- and H^+.
- High pO2 would not favor the formation either.
- High pCO2 is the correct answer as it leads to increased H^+ and HCO3^- formation.
- High alkalinity (high pH) would also not favor this reaction.

**Hint**: Evaluate each option based on the physiological processes discussed.

### Conclusion:
The factor in tissues that favors the formation of HCO3^- and H^+ ions in the blood is **high pCO2**. Thus, the correct answer is option 3: **high pCO2**.