Unless your professor is a huge dick, you should never have to answer more than what is directed of you in an exam question. I hear TAs complain when they have to grade papers, and people completely misinterpret the question being asked of them. So instead they go for a frantic shotgun approach of random information about the subject.
Lemme give you an example question with how I would answer it, and a bunch of fuckwaddery you are at liberty to skip if you want to.
QUESTION: Describe the permeability changes and movements of ions that occur during an action potential.
(when I read the word DESCRIBE, I see, "briefly explain what happens and how," not a bunch of hypothetical what if, theoretical BS.)
MY ANSWER: Starting with an electrical signal, the sodium ion gates open from the outside of the cell, causing Na+ (sodium) ions to flow into the cell, down their concentration gradient. As this occurs, the cell becomes progressively less polar (depolarization) and ultimately action potential occurs upon reaching threshold. Afterwards, the sodium ion gates close and the potassium ion gates in the membrane open and draw K+ (potassium) out of the cell in what is called repolarization. Finally, there is a temporary period of hyperpolarization, and this is due to an additional outflow of a few K+ ions while the K+ gates close.
(I asked if this answer was fine and the TA said yes, you'd get full credit. Did I miss some information? Yeah, but it wasn't relevant to what was being asked so I omitted it. Good enough, right?)
other people's questions: What if all the K+ leaves the cell? Why does X happen? Where does the electrical signal originate?
The answer to all 3 as far as the test question is concerned is IT DOESN'T FUCKING MATTER, got it?
The only reason I'm really bugged by these questions is when people don't realize that they're not the only student who needs assistance, and eat up my time and other student's time with stuff that's better saved for the professor's office hours.