Biology Forums - Study Force

a. increase their function in the small intestine due to increased hydrogen ion concentration.
b. decrease their function in the small intestine due to increased hydrogen ion concentration.
c. increase their function in the small intestine due to decreased hydrogen ion concentration.
d. decrease their function in the small intestine due to decreased hydrogen ion concentration

the answer is D. I considered both A and D.
decreased hydrogen ion concentration means more basic. peptidase functions best in a lower ph or more acid environment.
Yet I chose A because to the same tune.  Peptidase functions best in a low pH environment and similarly increasing the h+ concentration should make the environment more acidic and favorable for peptidase.
Can you please tell me what you would have chosen and why? Thank you.

This could be though about in two ways:

Way 1:

The rule of the thumb about enzymes is that they function optimally  in their normal locations in the body, any change in location will decrease their function. Else, why would the body use enzymes that are not optimal at a specific location?? makes no sense with the concept of evolution and development. The body is smart.

Thus now the answer is either b or d.

"Peptidases that function in the stomach most likely? " the question mentions the stomach so when the answers say "increased/decreased hydrogen ion concentration" , it means with respect to the hydrogen ion concentration in the stomach.

More Hydrogen ion concentration--> more H+ -->more Acidic( =less basic)

we know pH(intestine)>pH(stomach)
-->less acidic--> less H+ --> decreased Hydrogen ion concentration.

So the answer is D.

You have to be careful because they are specifically referencing the small intestines (not the stomach that falls in line with your reasoning). The small intestines has an overall basic pH of 6-8. The protein digesting enzymes in the stomach are only active in acidic environments.