endergonic vs. exergonic

endergonic vs. exergonic: What’s the difference?

In biochemistry, an endergonic chemical reaction is one that requires the input of energy (end- is a variant of endo- that means “inside” or “within”). An exergonic reaction is one that releases energy (ex- means “out”). In photosynthesis, the production of sugars by plants is an endergonic reaction—the energy input comes from sunlight. In cellular metabolism, the breakdown of sugars is an exergonic reaction—it releases energy for use.