I'm studying microbiology right now and I have come across something confusing to me. I thought electrons provided energy to the cell by being incorporated into reducing powers and eventually driving the synthesis of ATP. However in classification of microbes energy sources (photo, chemo) and electron sources (litho, organo) are separate.

Is there a scenario in which the source of electrons and energy are different (besides phototrophy)?

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    $\begingroup$ This is not a biological question and if you are studying microbiology, then you would have also learnt basic physics. I am voting to close this question. $\endgroup$ – WYSIWYG May 21 '15 at 11:50
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    $\begingroup$ I'm voting to close this question as off-topic because it is not about biology but basic physics. $\endgroup$ – Chris May 21 '15 at 11:52
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    $\begingroup$ I think there is an interesting question hidden here, but the formulation is throwing us off. Something on the lines of which energy sources does the cell use other than redox reactions of ATP. We could try translating "what does energy do that electrons can't do" as "what do other cellular energy sources do that ATP synthesis/cleaving can't" or something similar. $\endgroup$ – rumtscho May 21 '15 at 12:08
  • $\begingroup$ @rumtscho I still cannot understand what the actual question is. I am interpretting it like this — how different sources of energy translate to ATP production? $\endgroup$ – WYSIWYG May 21 '15 at 12:13
  • $\begingroup$ Electrons and Energy are 2 completely different thing. Electron is a class of negatively-charged sub-atomic particle. Energy is a concept, that is "ability of a system to do some work". You could consider it as "unstability" of a system $\endgroup$ – Always Confused Sep 7 '16 at 5:50

You're basically confusing the fuel source with the energy it produces. For example, a car burns gasoline. That doesn't mean that gasoline is energy, only that gasoline can be used to produce energy. Similarly, a cell uses electrons in the production of ATP (source):

ATP synthesis

In the image above, electrons (symbolized by the flat arrow going from $\mathit{NADH}$ + $H^+$ to $\frac{1}{2}O_2$ + $2H^+$) flow from NADH-Q reductase (I) to cytochrome reductase (III), to cytochrome oxidase (IV). The electron flow across these complexes causes the pumping of hydrogen cations (protons) through the membrane to the extracellular space. This, in turn, produces a pH gradient and membrane potential which are used to drive the synthesis of ATP (by the $F_1F_0$ ATPase), which can be broken down to release energy (source):

ATP hydrolysis

So, electrons are needed1 to produce ATP and ATP can be thought of as energy storage. When ATP is broken down to produce AMP and Phosphate, energy is released in the form of heat. This is why ATP is considered as "energy currency". Neither ATP nor electrons, however, are "energy" themselves2. No more than gasoline is.

1 Are used, anyway. There are other choices.

2 No more than any other form of matter, at least. You can, actually, think of matter as condensed energy but that is really squarely in the realm of physics and not biology.

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