The Question is from neet-botany morphology-of-flowering-polants leaf, and it was created by the author D VINOD

Question

In a CAM plant undergoing a prolonged drought, which physiological change would be MOST prominent in its leaves during the daytime?

D VINOD · Accepted Answer

## CORE INFORMATION
✓ **Answer**: B
## CONCEPT FRAMEWORK
 **Primary Concept**: Crassulacean Acid Metabolism (CAM) photosynthesis
 **Related Topics**: Plant adaptations to arid environments, stomatal regulation, carbon fixation pathways
 **Prerequisites**: Understanding of C3 and C4 photosynthesis, the roles of RuBisCO and PEP carboxylase.
## SOLUTION PATHWAY
**Given Information**:
  CAM plant, prolonged drought, daytime conditions.
  Important conditions: CAM plants minimize water loss by separating carbon dioxide uptake and fixation temporally.
**Method & Steps**:
 1. Consider the adaptations of CAM plants to drought conditions.
  Reasoning: CAM plants minimize water loss by opening their stomata at night to take in $CO_2$, which is then stored as malic acid. During the day, the stomata close to prevent water loss, and the stored malic acid is decarboxylated to release $CO_2$ for use in the Calvin cycle.
  Formula/Rule: None directly applicable, but understanding of CAM pathway is crucial.
 2. Analyze the options in the context of daytime physiology of a CAM plant under drought.
  Working: Option A is incorrect because stomata are closed during the day in CAM plants to conserve water. Option C is incorrect because while PEP carboxylase is involved, it's active at night, not during the day when the stomata are closed. Option D is incorrect because the Calvin cycle operates during the day, utilizing the $CO_2$ released from malate decarboxylation. Option B correctly describes the process of malate decarboxylation during the day, releasing $CO_2$ for the Calvin cycle while keeping stomata closed to minimize water loss.
  Key Point: The temporal separation of $CO_2$ uptake and fixation is the hallmark of CAM photosynthesis.
 3. Select the most prominent daytime physiological change.
  Result: Stomata remain closed, and malate is decarboxylated to release $CO_2$.
  Verification: This aligns with the known mechanism of CAM photosynthesis under drought stress.
 ## OPTION ANALYSIS
A :x: Stomata open during the day in CAM plants under drought conditions would lead to excessive water loss.
B ✓: Correctly describes the daytime physiology of a CAM plant under drought – stomata closed, malate decarboxylation releasing $CO_2$ for the Calvin cycle.
C :x: Stomata are typically closed during the day in CAM plants under drought conditions.
D :x: The Calvin cycle does not cease completely during the day in CAM plants; it utilizes the $CO_2$ released from malate.
 ## LEARNING AIDS
 **Common Mistakes**:
  1.Confusing CAM with C3 or C4 photosynthesis: Understanding the unique temporal separation of $CO_2$ uptake and fixation in CAM is crucial.
  How to avoid: Focus on the timing of stomatal opening and closure and the role of malic acid.
  2.Assuming stomata are always open during the day: Remember that CAM plants adapt to arid conditions by minimizing daytime transpiration.
  How to avoid: Understand the adaptive significance of stomatal closure during the day in CAM plants.
 **Quick Tips**:
  1.Remember the acronym CAM: Crassulacean Acid Metabolism – helps recall the key characteristics.
  2.Visualize the process: Imagine the nighttime $CO_2$ uptake and storage as malic acid, followed by daytime decarboxylation and use in the Calvin cycle.

D VINOD · Answer

Stomata open, and CO2 is directly fixed by RuBisCO.

D VINOD · Answer

The correct Option is "Stomata remain closed, and malate is decarboxylated to release CO2."

D VINOD · Answer

Stomata partially open, and PEP carboxylase fixes atmospheric CO2.

D VINOD · Answer

Stomata remain closed, and the Calvin cycle ceases completely.

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