That's what is called competitive enzymatic regulation. If there are more of that substance than the enzyme substrate, then most of the enzyme, if not all depending on the substance's concentration, will be inhibited on its action. If there are more substrate then the competitive substance, the expected reaction for that enzyme will happen at an expected rate. If the ratio substrate:substance is 1:1 then the reaction enzyme-substrate is very slowed down.
Involves actual transfer of electrons
Many kinds of prokaryotes and eukaryotes contain a structure outside the cell membrane called the cell wall. With only a few exceptions, all prokaryotes have thick, rigid cell walls that give them their shape. Among the eukaryotes, some protists, and all fungi and plants, have cell walls.
I believe that the answer would be Region D!
So the answer should be A!