Most of the carbon dioxide carried in the blood travels as

  • A. hydrogen carbonate ions dissolved in the plasma
  • B. carbaminohaemoglobin
  • C. carbon dioxide dissolved in the plasma
  • D. carbon monoxide

Explanation

About seventy per cent of carbon dioxide enters the red cells, where carbonic anhydrase converts it with water into carbonic acid, which dissociates into hydrogen and hydrogen carbonate ions, and the latter diffuse out into the plasma. Roughly twenty three per cent is carried on haemoglobin as carbaminohaemoglobin and only about seven per cent stays simply dissolved. The reactions reverse in the lungs.

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