Photorespiration starts when RuBisCO, instead of grabbing CO2, grabs oxygen and splits the RuBP molecule it is holding. This question asks what comes out of that split.
- Phosphoglycerate: Correct in part, one of the two fragments formed when RuBP reacts with oxygen is the three carbon compound 3-phosphoglycerate, the same molecule also made in normal carbon fixation.
- Phosphoglycolate: Also correct in part, the other fragment from the same reaction is the two carbon compound 2-phosphoglycolate, which is unique to the oxygenation route and has to be recycled through the photorespiratory pathway.
- Both A and B: Since the oxygenase reaction of RuBisCO on one RuBP molecule always gives one phosphoglycerate and one phosphoglycolate together, listing both as the product is the complete and accurate answer.
- Oxaloacetic acid: This compound belongs to the C4 carbon fixation cycle, made when PEP carboxylase fixes CO2, it does not come from the photorespiratory oxygenation reaction at all.
Because RuBisCO's reaction with oxygen breaks RuBP into these two fragments in one step, neither fragment alone tells the full story, so the pair together is the right answer.
Let's summarize:
- RuBP plus oxygen gives one 3-phosphoglycerate and one 2-phosphoglycolate.
- Oxaloacetic acid belongs to C4 fixation, not to photorespiration.
So option 3, both A and B, is the correct answer for the products of photorespiration.