A Level Biology Practice Exam

What effect does carbonic anhydrase have on blood pH?

1. It raises blood acidity

2. It lowers blood alkalinity

3. It stabilizes pH levels by facilitating CO2 excretion

4. It alters pH based on oxygen availability

The correct answer is: It stabilizes pH levels by facilitating CO2 excretion

Carbonic anhydrase plays a crucial role in maintaining pH homeostasis in the blood by catalyzing the reversible reaction between carbon dioxide (CO2) and water (H2O) to form carbonic acid (H2CO3). This reaction is pivotal in the transport and excretion of CO2 from the body. When CO2 levels rise in tissues, carbonic anhydrase facilitates the conversion of CO2 to carbonic acid, which can then dissociate into bicarbonate (HCO3-) and hydrogen ions (H+). The presence of H+ ions can lower pH (increase acidity); however, the bicarbonate acts as a buffer and helps to maintain a more stable pH level in the blood. By promoting the excretion of CO2 through respiration, carbonic anhydrase helps prevent major fluctuations in pH, effectively stabilizing it. This mechanism is vital for enabling the body to cope with varying metabolic demands and maintaining optimal conditions for cellular functions.