I won't be giving the actual question itself - just one I've changed the numbers in that is similar, so that I can get an idea of the method and can do it myself. Basically, Isolated mitochondria were initially incubated with stirring in a suitable buffer with a respiratory substrate and with phosphate. Under these initial conditions the rate of respiration (O2 consumption) was negligible. 18 µmol of ADP was then added which caused a burst of respiration which consumed 3 µmol of oxygen before the rate of respiration settled again to a negligible rate. Calculate the P/O ratio for mitochondria using this respiratory substrate. Now this is a really simplistic way of looking at this problem but initially I'd say 18/3 =6. But I'm not really sure about this because I'm not sure whether it goes to half O2, and how the reduced coenzymes affect this result. Succinate, for example only produces 2 ATP per oxygen (because it accesses via FADH2), but how about when you are looking at the entire electron transport chain? I'm having trouble finding good examples of how to work this, so any help would be very much appreciated.