In the `C_4` - plants , `C_4` cycle occurs in the mesophyll cells and `C_3` - cycle occurs in bundle sheath cells, whereas in CAM plants .

Options

A. `C_4 and C_3` - cycles occur in the mesophyll cells only
B. `C_4` - cycle occurs in bundle sheath cells and `C_3` - cycle in mesophyll cells
C. `C_4` - cycle very rarely
D. `C_4 and C_3` - cycles occur in bundle sheath cells

Answer

### Step-by-Step Solution:

1. **Understanding C4 and CAM Plants**:
- C4 plants, such as maize and sugarcane, have a unique photosynthetic pathway where the C4 cycle occurs in the mesophyll cells, and the C3 cycle occurs in the bundle sheath cells.
- CAM (Crassulacean Acid Metabolism) plants, like cacti and succulents, adapt to arid conditions by separating the C4 and C3 cycles temporally rather than spatially.

2. **Photosynthesis in CAM Plants**:
- In CAM plants, during the night, the stomata open to allow CO2 to enter the mesophyll cells.
- The CO2 is fixed into organic acids (like malate) and stored in the vacuoles of mesophyll cells.

3. **Daytime Photosynthesis**:
- During the day, the stomata close to reduce water loss, but the stored organic acids are converted back into CO2 in the mesophyll cells.
- This CO2 is then used in the C3 cycle for the synthesis of glucose.

4. **Identifying the Correct Option**:
- The question asks where the C4 and C3 cycles occur in CAM plants.
- In CAM plants, both the C4 cycle (fixing CO2 into organic acids) and the C3 cycle (using the fixed CO2 for sugar production) occur in the mesophyll cells.

5. **Conclusion**:
- The correct answer is that in CAM plants, both the C4 and C3 cycles occur in the mesophyll cells.

### Final Answer:
In CAM plants, both the C4 and C3 cycles occur in the mesophyll cells.

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