Formation of hydrogencarbonate ions:

Question 1

Formation of hydrogencarbonate ions:

Answer 1

• CO2 in blood plasma diffuses into erythrocytes where it combines with water to form carbonic acid (a
weak acid), catalysed by the carbonic anhydrase enzyme. CO2 + H20 -> H2CO3.
• The carbonic acid dissociates to release H+ ions and hydrogencarbonate ions (HCO3-). H2CO3 -> H+ +
HCO3-.
• The hydrogen carbonate ions diffuse out of the red blood cell into the blood plasma.
• The charge inside the erythrocyte is maintained
by chloride shift: the movement of Cl- ions from the plasma into the erythrocyte to maintain pH as HCO3- ions leave.
• The increase in H+ ions causes oxygen in oxyhaemoglobin to dissociate with haemoglobin due to the low partial pressure of oxygen caused by the H+ ions.

• Excess H+ ions are taken out of solution by associating with haemoglobin to produce haemoglobinic acid (HHb).
• The H+ ions building up in the red blood cell would cause the contents to become very acidic. In forming haemoglobinic acid, the haemoglobin is acting as a buffer – compound that maintains a constant pH.