Photosynthesis

Sometimes, RuBisCO acts like an assembly line worker falling asleep on the job.  It assembles the wrong parts, fixating oxygen to RuBP instead of carbon dioxide about 25% of the time!  This greatly reduces the efficiency of photosynthesis because the resultant molecule of fixated oxygen with RuBP cannot be used by the plant.

 

Photorespiration is like a superhero coming to the rescue and saving the molecules that have been wasted through the fixation of oxygen, called oxygenation.  However, calling this hero comes with a cost.  ATP is used up during photorespiration, and hydrogen peroxide builds up within the cell, which must be broken down into water and oxygen immediately by catalase.  To save one molecule of oxygen fixated to RuBP costs the plant one ATP molecule and one NADPH molecule.  

 

C4 and CAM plants have evolved to prevent oxygen from being fixated in place of carbon dioxide.