Problem 10 - Biology: The Dynamic Science

Question

The majority of \(\mathrm{CO}_{2}\) in the blood: a. is in the form of carbonic acid and bicarbonate ions b. dissociates to add \(\mathrm{H}^{+}\) to the blood to raise its \(\mathrm{pH}\) to 7.4 c. has a lower \(\mathrm{P}_{\mathrm{CO}_{2}}\), than the \(\mathrm{P}_{\mathrm{CO}_{2}}\) in the alveolar air. d. increases in the lung capillaries, which have a higher \(\mathrm{pH}\) than the tissue capillaries.

Step-by-Step Solution

Answer

Statements a and c are correct, while statements b and d are incorrect.

Step 1: Understanding the chemical properties of CO2 in the blood

CO2 in the blood exists in three forms: dissolved CO2, CO2 bound to hemoglobin, and bicarbonate ions (HCO3-). This derivation is facilitated by the enzyme carbonic anhydrase, which accelerates the reaction of CO2 with water to form carbonic acid (H2CO3). The carbonic acid then dissociates into HCO3- and H+.

Step 2: Evaluating statement a

Statement a is correct. The majority of the CO2 in the blood is indeed in the form of carbonic acid and bicarbonate ions.

Step 3: Evaluating statement b

Statement b is partially correct. When carbonic acid dissociates, it does yield a proton (H+). However, H+ does not raise the pH of the blood; it actually does the opposite. It lowers the pH of the blood, making it more acidic. Thus, statement b is considered incorrect.

Step 4: Evaluating statement c

Statement c suggests that the partial pressure of CO2 (PCO2) in the blood is lower than in the alveolar air. This is generally true, as alveolar air is where gas exchange occurs in the lungs, and CO2 moves from an area of higher PCO2 (i.e., the blood) to an area of lower PCO2 (i.e., the alveolar air to be exhaled). Thus, statement c is correct.

Step 5: Evaluating statement d

Statement d is incorrect. Although the pH level can influence CO2 levels, the pH in lung capillaries is not typically higher than in tissue capillaries. Also, PCO2 should decrease, not increase, in the lung capillaries during gas exchange.