Final answer:
An increase in blood PCO₂ in respiring tissues leads to increased bicarbonate and hydrogen ion concentrations, more carbaminohemoglobin, and more oxygen unloading from hemoglobin. However, it does NOT increase hemoglobin's affinity for oxygen; it decreases it.
Step-by-step explanation:
In respiring tissues, an increase in blood PCO₂ causes several physiological responses due to the transport and conversion of carbon dioxide in the bloodstream. As PCO₂ increases, carbon dioxide combines with water to form carbonic acid, which then dissociates into bicarbonate and hydrogen ions. This process results in an increase in the hydrogen ion concentration, leading to a decrease in blood pH, and a subsequent rise in bicarbonate concentration due to the conversion process facilitated by carbonic anhydrase.Additionally, more carbon dioxide is bound to hemoglobin to form carbaminohemoglobin, due to the increase in partial pressure of carbon dioxide, as predicted by the Haldane effect.
However, contrary to one of the options given in the question, an increase in blood PCO₂ does NOT lead to an increase in the affinity of hemoglobin for oxygen. Instead, it causes a decrease in the affinity of hemoglobin for oxygen, which leads to an increase in hemoglobin unloading of oxygen to the tissues. This is due to the rightward shift of the oxygen dissociation curve in the presence of more H+ ions (lower pH) and higher temperatures, as occurs in more actively respiring tissues.Therefore, the correct answer to the student's question is that in respiring tissues, an increase in blood PCO₂ causes all of the following EXCEPT an increase in the affinity of hemoglobin for oxygen (option d)