What is photosynthesis?

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What is photosynthesis?

The (too) simple answer

The simple answer: The process by which plants produce glucose and water from carbon dioxide and water:

carbon dioxide + water → glucose + oxygen

6CO2 + 6H2O → C6H12O6 + 6O2

However, simply mixing carbon dioxide and water together in a jar does not create glucose and oxygen (even if we add a catalyst). Why?

Well, if we look at the thermodynamics of this reaction it tells us that this reaction CANNOT work.

But plants do it

But wait!, as we all know from biology class plants can do photosynthesis.

Well, plants have a neat trick. The reaction above is not the only thing going on. They combine the photosynthesis reaction with another reaction:


where NADPH is Nicotinamide Adenine Dinucleotide Phosphate.


These two reactions combined can work. This behavior of combining two reactions in this way is known as coupling. It occurs quite frequently in nature.

Here thermodynamics indicates to us if a reaction can occur and provides us with some information as to how a process will work.

Note how thermodynamics tells us some information as to how the reaction proceeds.

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