I don't know, if it's a physics question, biology or chemistry question but anyways here it is:
I have been taught that to produce one molecule of glucose in photosynthesis, 18 ATP molecules are used up, but that in respiration, oxidation of the same glucose molecule releases 38 ATP molecules. I just can't seem to wrap my head around it. Where are these extra 20 ATP molecules coming from (or in other words extra 20 units of energy)?
I know there's a whole lot of reactions occurring in the cell that utilize energy, but the reactions of photosynthesis and respiration are reversible and I don't think the path to make or break glucose actually matters with respect to the amount of energy used or released in the processes. Glucose always remains glucose so of course writing the same reactions in reverse orders shouldn't change the energy used/given out in the reaction.
I really can't understand why it should it depend on the path by which glucose is used or made as many people have told me.
So in my opinion these two processes do seem to violate the law of conservation of energy, so please help!