A) haemoglobin is necessary for transport of carbon dioxide and carbonic anhydrase for transport of oxygen
B) haemoglobin is necessary for transport of oxygen and carbonic anhydrase for transport of carbon dioxide
C) only oxygen is transported by blood
D) only carbon dioxide is transported by blood
Correct Answer: B
Solution :
Transportation of\[{{O}_{2}}\]from lungs to body tissues and of \[C{{O}_{2}}\] from tissues to the lungs is vital role of blood. Transport of oxygen : About 97% of the \[{{O}_{2}}\] transported by blood is actually carried by the haemoglobin of RBCs. Haemoglobin is a complex heme protein formed of four subunits of coiled polypeptide chain and an iron-containing porphyrin ring. The iron of haemoglobin normally remains in reduced (Ferrous-\[\text{F}{{\text{e}}^{\text{++}}}\]) steate A molecule of \[{{O}_{2}}\] binds reversibely with each iron atom one after the other in such away that iron does not loss and electron and hence remains in ferrous condition. Oxygenated haemoglobin is called oxyhaemoglobin. \[H{{b}_{4}}+4{{O}_{2}}\xrightarrow[{}]{{}}Hb{{({{O}_{2}})}_{4}}\] The remaining 3% of \[{{O}_{2}}\] transported by blood is found dissolved in its plasma. Transport of carbon dioxide : Most of the \[C{{O}_{2}}\] that dissolves in blood plasma reacts with water to form carbonic acid : \[C{{O}_{2}}+{{H}_{2}}O\] \[{{H}_{2}}C{{O}_{3}}\] An enzyme carbonic anhydrase present in RBCs which accelerates the carbonic acid formation about 5000 times. About 70% of the \[C{{O}_{2}}\] received by blood from the tissue immediately enter into RBCs and hydrated to carbonic acid. All carbonic acid of RBCs dissociates into hydrogen and bicarbonate ions (\[{{H}^{+}}\] and\[HCO_{3}^{-}\]). The \[{{H}^{+}}\] mostaly combine with haemoglobin for keeping the pH of blood (7.4) in steady state whereas the bicarbonate ion diffuse from RBCs into the plasma. To maintain electrostatic neutrality of plasma many chloride ions in turn diffuse from plasma into RBCs. This is termed chloride or hamburger shift.
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