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Is it because CO2 is more soluble in water or has it got to do with the alkaline pH of plasma ?I here mean only aqueous CO2 transport from body cells to lungs.

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can you cite some support for this? offhand i would think that CO2 is more soluable in acid - it forms bicarbonate carbonic acid. –  shigeta Nov 11 '13 at 20:03
    
At what level do you mean? Are you talking about transporting from a source to a sink? CO2 is soluble in pure water, and as atmospheric partial pressures of CO2 are going to be lower than physiologic levels, any reversible buffering is just going to aid in transporting CO2 "downhill". –  Stuart R. Jefferys Nov 11 '13 at 23:08
    
By Dissolved state do you mean just the aqueous $\ce{CO2}$ molecules or those that are in form of $\ce{H2CO3}$ and $\ce{HCO3-}$ (free or associated) also? –  Satwik Pasani Nov 12 '13 at 6:38
    
Edited the question –  biogirl Nov 12 '13 at 17:30
    
Solubility of gases is affected by the chemical nature of the gas. Acidic oxides dissolve in water readily because they react to form acids. The high pH can keep the acid dissociated thereby pulling the gas-acid equilibrium towards acid. CO2 is more soluble, in general, than nitrogen and oxygen because it is polar (however it lacks net dipole moment) –  WYSIWYG Nov 13 '13 at 5:20
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The bulk of CO2 is transported as bicarbonate/carbonic acid. The conversion between CO2 and carbonic acid is catalyzed by carbonic anhydrase in red blood cells, otherwise the conversion would be very slow. The bicarbonate is then shuttled out of the RBCs and into the blood plasma. The CO2 (gas) in blood plasma accounts for <10% of CO2 transport, and the solubility isn't that much different from that in water.

Source: Guyton and Hall Textbook on Medical Physiology

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about the same amount of CO2 is transported by hemoglobin... –  shigeta Nov 12 '13 at 17:46
    
Hemoglobin actually doesn't carry very much CO2, as it doesn't have a dedicated spot to carry it. There is a binding site on the protein, but its purpose is to facilitate the release of extra oxygen to metabolically active tissues. –  Andrew Bonnell Nov 12 '13 at 20:21
    
... in fact only 10% of it! see wikipedia: Hemoglobin. –  shigeta Nov 13 '13 at 4:20
    
Haemoglobin cannot bind CO2. It is not a good ligand for metal co-ordination complexes. However carbon monoxide is a strong ligand and can form carbonyls with metals, which accounts for its toxicity. –  WYSIWYG Nov 13 '13 at 5:22
    
@shigeta - I thought you were saying hemoglobin carries as much CO2 as bicarbonate transport does...my mistake! –  Andrew Bonnell Nov 13 '13 at 15:03
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