Which of the following is not a way carbon dioxide travels in the blood?

Carbon dioxide is transported in the blood from the tissue to the lungs in three ways:1 (i) dissolved in solution; (ii) buffered with water as carbonic acid; (iii) bound to proteins, particularly haemoglobin.

Approximately 75% of carbon dioxide is transport in the red blood cell and 25% in the plasma. The relatively small amount in plasma is attributable to a lack of carbonic anhydrase in plasma so association with water is slow; plasma plays little role in buffering and combination with plasma proteins is poor.

There is a difference between the percentage of the total carbon dioxide carried in each form and the percentage exhaled from them. For example, 5% of the total is in solution but 10% of exhaled carbon dioxide comes from this source; 10% is protein bound, particularly with haemoglobin, but this supplies 30% of the exhaled amount.

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