Acid concentration in CAM plants is more at

Options

A. night
B. daytime
C. dawn
D. dusk

Answer

To answer the question about when acid concentration is more in CAM plants, we can follow these steps:

### Step-by-Step Solution:

1. **Understand CAM Plants**: CAM stands for Crassulacean Acid Metabolism. These plants have adapted to arid conditions and have a unique method of carbon fixation.

2. **Stomatal Behavior**: In CAM plants, the stomata (tiny openings on leaves) open at night and close during the day. This is a crucial adaptation to minimize water loss during the hotter daytime.

3. **Carbon Dioxide Uptake**: During the night, when the stomata are open, carbon dioxide (CO2) enters the plant. This is the time when the plant can fix CO2 without losing much water.

4. **Formation of Organic Acids**: The enzyme phosphoenolpyruvate carboxylase (PEP carboxylase) fixes the CO2 into a four-carbon compound called oxaloacetate, which is then converted into malate (an organic acid).

5. **Acid Accumulation**: As a result of this process, the concentration of organic acids, particularly malate, increases during the night when the stomata are open and CO2 is being fixed.

6. **Daytime Photosynthesis**: During the day, the stomata close to prevent water loss, and the stored malate is used in the process of photosynthesis.

### Conclusion:
Thus, the acid concentration in CAM plants is more at **night** when the stomata are open, and CO2 is being fixed into organic acids.

---