Your book is much more 'sketchy' about this half of photosynthesis. It covers the rather recent history of discovery briefly. It did a perfunctory job of showing you the reactions themselves...
Photorespiration is a problem with the enzyme RUBISCO. It binds both CO2 and O2...and the O2 combination takes RUBP apart into CO2 rather than building trioses for sugar synthesis. Worse, you get no ATP from photorespiration!
Solutions: C-4 Photosynthesis and CAM (another C-4 system)
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