- A Can bind O2 as well as CO2 when CO2 is low and O2 is high
- B Functions mainly at night, away from light reactions
- C Binds only CO2, regardless of ambient O2 levels
- D Is largely absent from mesophyll cells in C3 leaves
Correct answer: A. Can bind O2 as well as CO2 when CO2 is low and O2 is high
Explanation: Rubisco has both carboxylase and oxygenase activity; under high O2/low CO2 conditions, it binds O2 instead, initiating photorespiration, which consumes energy without fixing carbon or producing sugar.
Concept context
Light reactions, the Calvin cycle, C3/C4/CAM pathways, photorespiration, and factors affecting the rate of photosynthesis. One of the highest-yield NEET chapters.