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Disclaimer: This question is kind of sprayed over biology, chemistry and physics.

Anyway, I had to learn more about photosynthesis recently, and although it is quite complex, I think I got it - except for one thing: Everywhere it is basically just said, that chloroplasts convert light energy into chemical energy. But seemingly no one is interested in how they do it. I couldn't find an explanation after some googling. Not even Wikipedia had something for me (at least nothing I was able to sort out of the technical jargon).

So my question now is: What exactly happens in this process? It'd be good if the answer wouldn't include to much jargon, because I'm not really experienced in the field. (Just the usual knowledge and a little more due to being interested in science in general).

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    $\begingroup$ The overall process is photosynthesis, the chloroplast is the structure that accomplishes this in most photosynthesizing organisms. You'll find a description in any Biology text. Here's a reference with diagrams to illustrate the role of the chloroplast: www2.estrellamountain.edu/faculty/farabee/BIOBK/BioBookPS.html $\endgroup$
    – bpedit
    Oct 5, 2016 at 16:09
  • $\begingroup$ @bpedit Thanks, that is already a little more information. It states In the Light Dependent Processes (Light Reactions) light strikes chlorophyll a in such a way as to excite electrons to a higher energy state. In a series of reactions... But it doesn't mention what these reactions are. The electrons gain more energy, but that's only part of the answer. $\endgroup$
    – Namnodorel
    Oct 5, 2016 at 16:35
  • $\begingroup$ Your question is broad. Please narrow it down to a specific issue. $\endgroup$
    – WYSIWYG
    Oct 6, 2016 at 17:50
  • $\begingroup$ @WYSIWYG You did notice that there is already an accepted answer which provides exactly the information I asked for, right? And I don't think that the question is too broad. "What exactly happens when the light is turned into chemical energy" is quite specific I think. What would you have needed to understand it better? $\endgroup$
    – Namnodorel
    Oct 6, 2016 at 21:00
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    $\begingroup$ @AlwaysConfused Okay, I can see that. Better now? $\endgroup$
    – Namnodorel
    Oct 14, 2016 at 17:46

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I see you've given this a try, so here's a synopsis hopefully appropriate to both your current knowledge level and curiosity.

Light excites electrons in chlorophyll to a higher energy. Higher energy means less stable, those electrons want to return to a state of lower energy. The chloroplast is structured in such a way that the electrons, instead of just plopping back to the lower energy state in the chlorophyll to liberate the light they just absorbed, are handed off to another molecule. As the electrons get passed off to other molecules, they lose energy. All of this is taking place on a membrane within the chloroplast. The energy being "lost" by the electrons is harnesed to pump hydrogen ions across that "thylakoid" membrane in the cholorplast. The increased concentration of H+ within the thylakoid space is another form of energy that can do work. The work done is the creation of ATP.

We're not done with those electrons yet. They get passed off to yet more molecules, losing energy again in each hand-off. This energy is used to create additional energy-rich substances that will power the creation of energy-rich organic molecules in a process termed the Calvin Cycle. The Calvin Cycle, which creates the sugar G3P from inorganic CO2 from the atmosphere, also takes place within the chloroplast.

So, the chloroplast is a multi-talented factory for the conversion of CO2 into sugars. These sugars provide both energy and carbon, in a useable organic form, for other processes in the plant. Chloroplasts also contain DNA. This, and other evidence, suggests that chloroplasts, like mitochcondria, were once free living organisms that got co-opted by other organisms and now exist within cells in a mutualistic association (the Endosymbiont Theory).

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  • $\begingroup$ Thanks a lot, finally a good explanation ^^ I'll probably need to think multiple times over this to fully understand it, but it is something to work with :) $\endgroup$
    – Namnodorel
    Oct 5, 2016 at 17:31

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