Subject: How do we know the specifics about the electron transport chain?

I teach 10th grade biology.  When I am explaining fairly intricate 
biological processes such as cellular respiration, my students often ask 
questions related to the discovery of such processes.  For example, what 
methods did researchers use to determine that compounds such as FAD, NAD, 
and GTP were important in glycolysis and respiration?  I believe this to be 
a legitimate question.  Considering the number and variety of biochemical 
reactions constantly operating in a cell, it must have been quite a 
challenge to develop such a detailed and numerically specific (e.g., 36 
ATP) map of cellular repiration.  Any information on the names of 
researchers or methods used is appreciated.

Thanks in advance.

Re: How do we know the specifics about the electron transport chain?