- A It is sometimes thought to function mainly at unusually high temperatures well above the normal physiological leaf range found in nature
- B It has low catalytic rate (kcat ~3/sec) and reacts with O2 as well as CO2 (oxygenase activity), causing photorespiration
- C It is sometimes thought to require rare transition metal cofactors that are absent from typical photosynthetic leaf tissue altogether
- D It is sometimes thought to become catalytically active mainly when CO2 concentration far exceeds normal atmospheric levels found outdoors
Correct answer: B. It has low catalytic rate (kcat ~3/sec) and reacts with O2 as well as CO2 (oxygenase activity), causing photorespiration
Explanation: Rubisco: very slow turnover (~3 CO2/sec vs ~1000 for typical enzymes). Cannot fully discriminate between CO2 and O2. At high O2/low CO2, adds O2 (photorespiration), wasting energy.
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.