Breathing And Exchange Of Gases

About seventy per cent of carbon dioxide is transported in blood as bicarbonate ions. As outlined in NCERT Class 11, Chapter 17 (Breathing and Exchange of Gases), the enzyme carbonic anhydrase inside red blood cells rapidly converts carbon dioxide and water into carbonic acid, which dissociates into hydrogen ions and bicarbonate ions. As bicarbonate diffuses out of the erythrocyte into the plasma, chloride ions move from the plasma into the cell to preserve electrical neutrality; this inward migration is the chloride shift, also called the Hamburger phenomenon. The Bohr effect is different: it describes how rising carbon dioxide and falling pH reduce haemoglobin's oxygen affinity, which concerns oxygen unloading rather than ionic balance. The sodium pump is an active transport mechanism for sodium and potassium across membranes, unrelated to carbon dioxide carriage. Countercurrent exchange describes opposed fluid flows enhancing transfer, as in the kidney's loop of Henle, not events within a red cell. Hence chloride shift is correct. A consistency check confirms it: maintaining neutrality after an anion leaves a cell requires an equivalent anion entering, and chloride entry exactly balances bicarbonate exit.