The first stable product of CAM cycle is

Options

A. Oxalic acid
B. Malic acid
C. Oxalo-acetic acid
D. Pyruvic acid

Answer

### Step-by-Step Solution

1. **Understanding CAM Cycle**: The CAM (Crassulacean Acid Metabolism) cycle is a photosynthetic process found in certain plants, particularly those in arid environments. These plants have adapted to conserve water by opening their stomata at night instead of during the day.

2. **Stomatal Behavior**: In CAM plants, stomata are closed during the day to minimize water loss through transpiration. Instead, they open at night to take in carbon dioxide (CO2) when temperatures are cooler and humidity is higher.

3. **Carbon Dioxide Fixation**: During the night, when the stomata are open, CO2 is fixed. The primary carbon dioxide acceptor in this process is phosphoenolpyruvic acid (PEP), which is a 3-carbon compound.

4. **Formation of Oxaloacetic Acid**: When CO2 is fixed by PEP, it forms oxaloacetic acid (OAA), which is a 4-carbon compound. This reaction is catalyzed by the enzyme PEP carboxylase.

5. **First Stable Product**: The first stable product of the CAM cycle is oxaloacetic acid (OAA). This compound is then converted into malate, which is stored until daytime when it is decarboxylated to release CO2 for the Calvin cycle.

6. **Conclusion**: Therefore, the first stable product of the CAM cycle is **oxaloacetic acid**.

### Final Answer
The first stable product of the CAM cycle is **oxaloacetic acid**.

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