Question

Band 3 is unusual in that it can transport HCO3 in exchange for Cl ions, in either direction, via passive transport. Why is it important that Band 3 operate in both directions?

Answer 1

answer) because the basic role of this anion exachanger is in the red blood cells. In the tissues the co2 which diffuses in RBC rapidly converted into bicarbonate and proton with the help of carbonic anhydraseII and this bicarbonate are transported out of the cell in return chloride and proton buffered by the cell. now in the lung system reverses and bicarbonnate enters the cell in exchange of chloride , bicarbonate and proton is converted into carbondioxide and water with the help of carbonic anhydraseII and then the co2 difuses outof the red blood cells.

so we can say that this anion exchanger should work in both direction so it can serves the both tissues and lungs for the exchange of co2 and o2.