What happens when the parietal cells of gut epithelium becomes partially non-functional?
Parietal cells are responsible for acid secretion (HCl) in the stomach.

pH is inversely correlated to H+ concentration; the higher the H+ concentration, the lower the pH.

If the stomach's parietal cells become partially non-functional, there will be less acid secreted into the stomach (a lower H+), and the pH will rise. 

Answer (b) 


  (b) The pH of the stomach will fall abruptly


is the opposite of what would be expected to occur. 

The correct answer is d), for the reason you listed. 


  Proteins will not be adequately hydrolysed by pepsin into proteoses and peptones.


Regulation of Acid Secretion