52. Which of the following statements are TRUE with regard to the similarities between
Crassulacean Acid Metabolism (CAM) and C4 cycle?
P. Stomata open during night and remain closed during the day
Q. PEPcase is the carboxylating enzyme to form C4 acid
R. C4 acid is decarboxylated to provide CO2 for C3 cycle
S. Kranz anatomy is predominant in both CAM and C4 plants
(A) P, S
(B) Q, R
(C) P, Q
(D) R, S

Crassulacean Acid Metabolism (CAM) and C4 pathways both enhance CO2 efficiency in plants, but differ in timing and anatomy. This article breaks down MCQ question 52 on their similarities, revealing the correct answer as (B) Q, R.

Question Breakdown

The query tests core photosynthetic adaptations in arid-adapted plants. CAM operates temporally (night CO2 fixation), while C4 uses spatial separation (mesophyll/bundle sheath). True similarities center on shared biochemical steps.​

Option Analysis

• P. Stomata open during night and remain closed during the day: True for CAM plants, which fix CO2 nocturnally via open stomata to minimize water loss. C4 plants, however, open stomata during the day like C3 plants. Thus, not a shared trait.​

• Q. PEPcase is the carboxylating enzyme to form C4 acid: True for both. Phosphoenolpyruvate carboxylase (PEPcase) fixes CO2 into oxaloacetate (C4 acid) in CAM at night and in C4 mesophyll cells during day.​

• R. C4 acid is decarboxylated to provide CO2 for C3 cycle: True for both. Malate (from C4 acid) decarboxylates daytime in CAM (behind closed stomata) and in C4 bundle sheath, supplying CO2 to Rubisco in Calvin (C3) cycle.​

• S. Kranz anatomy is predominant in both CAM and C4 plants: False. Kranz (wreath-like) anatomy with bundle sheath cells defines C4 plants. CAM plants lack this; they use ordinary mesophyll with large vacuoles for malate storage.​

Correct Answer: Why (B) Q, R?

Options Q and R highlight biochemical parallels: both pathways use PEPcase for initial C4 carboxylation and decarboxylation to concentrate CO2 for Rubisco, reducing photorespiration. P suits only CAM’s temporal strategy, S only C4’s anatomy. Options (A), (C), (D) mix false similarities.