Test: MCAT Biology

Among the most important pH buffer systems in humans is the bicarbonate buffer, which keeps the blood at a remarkably precise 7.42 pH. The bicarbonate buffer system uses a series of important compounds and enzymes to make the system function. Figure 1 depicts the key reactions that take place.

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The activity of this buffer system is mainly controlled by the renal and respiratory systems. The renal system excretes bicarbonate in the urine, while the respiratory system “blows off” carbon dioxide as needed. By balancing these two systems as needed, blood pH is maintained in such a narrow range.

1.

Carbonic anhydrase is an organic enzyme. Which of the following is true of carbonic anhydrase? Assume no CO2 or bicarbonate is lost in the reaction.

I. It lowers the activation energy for the conversion of carbon dioxide to carbonic acid

II. It shifts the equilibrium toward carbon dioxide in experimental conditions

III. It modifies chemical species at its allosteric site

I, II, and III

I and II

III, only

I, only

I and III

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