A Level Biology Practice Exam

What is the purpose of the chloride shift in red blood cells?

1. To exchange oxygen and carbon dioxide

2. To maintain electrochemical equilibrium

3. To facilitate the absorption of nutrients

4. To regulate blood pH levels

The correct answer is: To maintain electrochemical equilibrium

The chloride shift in red blood cells primarily serves to maintain electrochemical equilibrium. When carbon dioxide is transported in the blood, particularly as bicarbonate (HCO3-), it enters the red blood cells and combines with water to form carbonic acid (H2CO3), which dissociates into bicarbonate and hydrogen ions. To keep charge neutral, chloride ions (Cl-) move into the red blood cells as bicarbonate ions move out into the plasma. This exchange helps to balance the charges between the inside of the red blood cells and the plasma, maintaining electrochemical stability, which is crucial for proper cell function. While the movement of gases like oxygen and carbon dioxide is essential for respiration, the specific action of chloride ions in this shift is focused on ensuring that the cell remains electrically neutral during the biochemical processes involved in gas transport. This mechanism does not directly involve nutrient absorption or regulation of pH levels, although it indirectly affects blood pH by influencing the concentration of hydrogen ions in the blood.