Given below are two statements:
Statement (I): In CAM plants the stomata open at day time and a large amount of carbon dioxide is fixed as malic acid which is stored in vacuoles.
Statement (II): In CAM plants, during night time as the stomata are closed, there is no possibility of carbon di oxide entry.
In light of the above statements, choose the most appropriate answer from the options given below.
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CAM plants have nocturnal stomatal behavior to save water:
- Night: Stomata OPEN, \(\text{CO}_2\) enters and is stored as malic acid (acidification phase).
- Day: Stomata CLOSED, malic acid releases \(\text{CO}_2\) internally for the Calvin cycle (deacidification phase).
Statement (I) is true but Statement (II) is false.
Statement (I) is false but Statement (II) is true.
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The Correct Option isB
Solution and Explanation
Step 1: Understanding the Concept:
Crassulacean Acid Metabolism (CAM) is a specialized photosynthetic carbon fixation pathway found in desert-adapted plants, such as pineapples, cacti, and agaves.
This pathway is an evolutionary adaptation designed to maximize water-use efficiency in arid environments by separating carbon dioxide capture and light reactions temporally (between day and night). Step 2: Detailed Explanation:
Let us analyze both statements to evaluate their validity:
- Statement (I): In CAM plants, to minimize water loss through transpiration under hot desert conditions, the stomata remain closed during the hot daytime.
Instead, the stomata open at night when temperatures are cooler and relative humidity is higher.
During the night, carbon dioxide enters the open stomata and is fixed by the enzyme PEP carboxylase into oxaloacetate, which is converted to malic acid and stored inside large vacuoles.
Therefore, Statement (I) is incorrect because it states that stomata open during the day and fix carbon dioxide into malic acid then.
- Statement (II): As explained above, the stomata of CAM plants are open at night, allowing carbon dioxide to enter.
During the day, the stomata are closed to prevent water loss.
The stored malic acid is then transported out of the vacuoles and decarboxylated to release carbon dioxide internally, which is fixed by Rubisco using light energy via the Calvin cycle.
Therefore, Statement (II) is incorrect because it states that stomata are closed at night and prevent carbon dioxide entry.
Since both statements are incorrect, option (B) is the correct choice. Step 2: Final Answer:
Both Statement (I) and Statement (II) are false.
