Select the statement that is not correct from the following.

Options

A. Plants which utilizes first , RuBP in `CO_2` fixations are called `C_3` plants.
B. Plants which utilizes first , PEP in `CO_2` fixations are called `C_2` plants.
C. CAM plants lack structural compartmentalization of leaf , as found in `C_4` plants .
D. `C_4` photosynthetic pathway is more efficient than the `C_3` pathway.

Answer

To solve the question of identifying the incorrect statement regarding plant photosynthesis, we will analyze each statement provided in the options step by step.

### Step-by-Step Solution:

1. **Understanding C3 Plants**:
- C3 plants utilize ribulose 1,5-bisphosphate (RuBP) in the process of carbon dioxide fixation. The first stable product formed is 3-phosphoglycerate (3-PGA).
- **Conclusion**: The statement "Plants which utilize first ribulose 1,5-bisphosphate in carbon dioxide fixation are called C3 plants" is correct.

2. **Understanding C4 Plants**:
- C4 plants utilize phosphoenolpyruvate (PEP) in carbon dioxide fixation, leading to the formation of four-carbon compounds (oxaloacetate).
- **Conclusion**: The statement "Plants which utilize first phosphoenolpyruvate in carbon dioxide fixation are called C4 plants" is correct. The statement in the question incorrectly refers to them as C2 plants.

3. **Understanding CAM Plants**:
- CAM (Crassulacean Acid Metabolism) plants, such as cacti, fix carbon dioxide at night when their stomata are open and store it as malate. They lack the structural compartmentalization seen in C4 plants, which have a specific leaf anatomy known as Kranz anatomy.
- **Conclusion**: The statement "CAM plants lack structural compartmentalization of leaf as found in C4 plants" is correct.

4. **Efficiency of C4 vs. C3 Pathways**:
- The C4 photosynthetic pathway is indeed more efficient than the C3 pathway, especially in conditions of high light intensity and temperature, as it minimizes photorespiration.
- **Conclusion**: The statement "C4 photosynthetic pathway is more efficient than the C3 pathway" is correct.

### Final Conclusion:
The statement that is **not correct** is: "Plants which utilize first phosphoenolpyruvate in carbon dioxide fixation are called C2 plants." This is incorrect because they are referred to as C4 plants.

### Answer:
The incorrect statement is: "Plants which utilize first phosphoenolpyruvate in carbon dioxide fixation are called C2 plants."

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