- A An adaptation enabling survival specifically in persistently cold, frost-prone alpine and arctic mountain climates in routine practice
- B Adaptation to arid conditions -- temporally separating CO2 fixation (night) from Calvin cycle (day) to minimize water loss
- C An adaptation for capturing limited light filtering down through deeply shaded forest understory regions overall in most cases
- D An adaptation allowing root respiration to continue normally within waterlogged, oxygen-poor soil environments under typical conditions
Correct answer: B. Adaptation to arid conditions -- temporally separating CO2 fixation (night) from Calvin cycle (day) to minimize water loss
Explanation: CAM: evolved in desert plants (cacti, agaves, succulents) for maximal water use efficiency. Night CO2 fixation (PEP carboxylase) stores CO2 as malate; day decarboxylation feeds Calvin cycle with stomata closed.
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.