Approximately seventy percent of carbondioxide absorbed

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Approximately seventy percent of carbondioxide absorbed by the blood will be transported to the lungs:

1. as bicarbonate ions
2. in the form of dissolved gas molecules
3. by binding to R.B.C.
4. as carbamino - haemoglobin

Correct Option: A

CO₂ from the respiratory tissues to the lungs is transported by the blood in 3 ways:
(i) In dissolved state or as a physical solution: Very small amount is physically dissolved in plasma (7% i.e. ≅ 0.3 ml of CO₂ by each 100 ml of blood).
(ii) Bicarbonate ions: ≅ 70% (i.e. ≅ 2.5 ml per 100 ml of blood) CO₂ diffuses in plasma & then into RBCs where it (in the presence of carbonic anhydrase) combines with H₂O to form carbonic acid which is almost spontaneously dissociated into hydrogen ion and bicarbonate ions.
(iii) Carbaminohaemoglobin: ≅ 23% (i.e. ≅ 1 ml of CO₂ per 100 ml of blood) combines with haemoglobin forming an unstable compound.