Statemeent A: carbonic anhydrase present in RBCs facililates the formation of bicarbonate ions at tissue level. Statement B: The same enzyme facilitates the formation of CO_2 in RBCs at alveoli level.

Options

A. both statements are correct
B. statement A is correct and B is incorrect
C. statement A is incorrect and B is correct
D. both statements are incorrect

Answer

To analyze the statements regarding carbonic anhydrase, we will break down the processes described in each statement step by step.

### Step 1: Understanding Statement A
- **Statement A** claims that carbonic anhydrase present in red blood cells (RBCs) facilitates the formation of bicarbonate ions at the tissue level.
- In tissues, carbon dioxide (CO₂) produced by cellular respiration diffuses into the RBCs.
- Inside the RBCs, CO₂ reacts with water (H₂O) to form carbonic acid (H₂CO₃) through the action of carbonic anhydrase.
- Carbonic acid then dissociates into bicarbonate ions (HCO₃⁻) and hydrogen ions (H⁺).
- Therefore, Statement A is correct.

### Step 2: Understanding Statement B
- **Statement B** states that the same enzyme (carbonic anhydrase) facilitates the formation of CO₂ in RBCs at the alveoli level.
- In the alveoli, the process is reversed. Bicarbonate ions (HCO₃⁻) that were formed in the tissues re-enter the RBCs.
- Inside the RBCs, bicarbonate ions combine with hydrogen ions to form carbonic acid (H₂CO₃).
- Carbonic acid then dissociates into water (H₂O) and carbon dioxide (CO₂), which is released into the alveoli to be exhaled.
- Thus, Statement B is also correct.

### Conclusion
Both statements A and B are correct regarding the role of carbonic anhydrase in the formation of bicarbonate ions at the tissue level and the formation of carbon dioxide at the alveoli level.