Question

Given below are two statements, one is labelled as Assertion (A) and other one labelled as Reason (R).
Assertion (A) : The CAM plants undergo night time acidification and day time deacidification.
Reason (R) : The CAM plants take up $\text{CO}_2$ during day time, store it in the form of malate in vacuoles and break it down to release $\text{CO}_2$ in the night time.

• A. Both (A) and (R) are true and (R) is the correct explanation of (A).
• B. Both (A) and (R) are true but (R) is NOT the correct explanation of (A).
• C. (A) is true but (R) is false.
• D. (A) is false but (R) is true.

Hint:

CAM plants open their stomata at night to prevent desiccation. Hence, carbon dioxide uptake and the resulting acidification (malic acid accumulation) can only happen at night.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Crassulacean Acid Metabolism (CAM) is a photosynthetic adaptation found in succulent plants growing in arid regions.
To minimize water loss, these plants separate carbon dioxide capture and the Calvin cycle temporally between night and day.

Step 2: Detailed Explanation:
Let us analyze the Assertion and the Reason individually:
- Assertion (A) is true: CAM plants open their stomata at night to capture carbon dioxide.
This carbon dioxide is fixed into malic acid, which is stored in vacuoles overnight, causing a decrease in vacuolar pH (night-time acidification).
During the day, stomata remain closed to prevent transpiration, and the stored malic acid is transported out of the vacuoles and decarboxylated to release carbon dioxide for the Calvin cycle, causing the pH to rise (day-time deacidification).
- Reason (R) is false: The statement describes the reverse of the actual CAM process.
CAM plants capture carbon dioxide during the night (not day-time) when transpiration rates are low.
They store this carbon dioxide as malate in their vacuoles overnight.
During the day (not night-time), they close their stomata and break down this stored malate to release carbon dioxide for the light-independent reactions.
Therefore, Assertion (A) is true but Reason (R) is false.

Step 3: Final Answer:
The correct option is: (A) is true but (R) is false.