Kranz anatomy is observed in :

Question

Accepted Answer

Kranz anatomy is observed in $C_4$ plants, which is why Option 3 is the correct answer. Here's a detailed explanation:

1. **Explanation for Option 3 ($C_4$ plants):**
   - Kranz anatomy is a specialized structure in the leaves of $C_4$ plants. It is characterized by the presence of bundle sheath cells that surround the vascular bundles. These cells are large and contain chloroplasts, which are crucial for the $C_4$ photosynthetic pathway.
   - In $C_4$ plants, photosynthesis is divided between mesophyll cells and bundle sheath cells. Carbon dioxide is initially fixed in the mesophyll cells into a four-carbon compound (hence the name $C_4$) and then transported to the bundle sheath cells, where the Calvin cycle occurs. This anatomical adaptation helps minimize photorespiration and increases the efficiency of photosynthesis, especially under conditions of high light intensity, high temperatures, and low atmospheric CO2 concentrations.

2. **Explanation for why other options are incorrect:**

- **Option 1 ($C_2$ plants):**
     - There is no recognized category of $C_2$ plants in the context of photosynthesis. The term $C_2$ is not used to describe any specific photosynthetic pathway or plant anatomy. Therefore, Kranz anatomy cannot be associated with $C_2$ plants.

- **Option 2 ($C_3$ plants):**
     - $C_3$ plants do not exhibit Kranz anatomy. In $C_3$ plants, the Calvin cycle occurs in the mesophyll cells, and there is no separation of initial CO2 fixation and the Calvin cycle as seen in $C_4$ plants. The lack of Kranz anatomy in $C_3$ plants means they are more susceptible to photorespiration, especially under conditions of high temperature and light intensity.

- **Option 4 (CAM plants):**
     - CAM (Crassulacean Acid Metabolism) plants have a different adaptation for photosynthesis, which involves temporal separation of CO2 uptake and fixation. They do not exhibit Kranz anatomy. Instead, CAM plants open their stomata at night to fix CO2 into organic acids, which are then used during the day for photosynthesis. This adaptation helps them conserve water in arid conditions but does not involve the structural features of Kranz anatomy.

In conclusion, Kranz anatomy is a distinctive feature of $C_4$ plants, making Option 3 the correct answer.