HCO3-/H2CO3 is considered most effective buffer at physiological pH because
a) It has pKa close to physiological pH
b) It is formed from a weak acid and base
c) Its components can be increased or decreased by the body
d) It can donate and accept H+
According tp Henderson Hasselbalch equation
pH=pKa + log [HCO3-]/[H2CO3]
The physiological pH is 7.4,In case of bicarbonate buffer
pH=6.1+ log 24/1.2=6.1 +log20=6.1+1.3=7.4,which is exactly equal to physiological pH.
Hence bicarbonate buffer is most effective buffer due to two reasons
1.The concentration of [HCO3-] is very high ie 24mmol/l hence the ratio is maintained at
20,hence pH can be maintained.
2.The components is under physiological control ie
[HCO3-] can be regulated by kidneys
CO2 ,hence Carbonic acid [H2CO3] is regulated by lungs.So any imbalance in [HCO3-
]/[H2CO3] can regulated by renal or respiratory method and ratio 20 can be maintained