The guard cells of Stomata in land plants are specialized epidermal cells which contains chloroplast. In rest of epidermal cells chloroplast are absent.
So option " D " is correct answer.

Guard Cells in Land Plants

Guard cells are specialized cells found in the epidermis of plant leaves and stems. They play a crucial role in regulating the exchange of gases, particularly carbon dioxide and oxygen, as well as the loss of water vapor through small openings called stomata.

Difference Between Guard Cells and Other Epidermal Cells

Among the various epidermal cells, guard cells possess certain unique features that distinguish them from other cells:

1. Chloroplasts
- Guard cells contain chloroplasts, which are responsible for photosynthesis, the process by which plants convert light energy into chemical energy.
- Chloroplasts contain chlorophyll, the pigment that gives plants their green color and is essential for capturing sunlight.
- The presence of chloroplasts in guard cells enables them to produce energy through photosynthesis and actively regulate stomatal opening and closing.

2. Cytoskeleton
- Both guard cells and other epidermal cells possess a cytoskeleton, a network of protein filaments that provide structural support and help maintain cell shape.
- The cytoskeleton is involved in various cellular processes, including cell division, movement, and transport.
- While guard cells have a cytoskeleton, it is not a distinguishing feature that sets them apart from other epidermal cells.

3. Mitochondria
- Mitochondria are the powerhouses of the cell, responsible for generating energy in the form of ATP through cellular respiration.
- Both guard cells and other epidermal cells contain mitochondria to produce energy for cellular processes.
- Therefore, the presence of mitochondria is not a unique characteristic of guard cells.

4. Endoplasmic Reticulum
- The endoplasmic reticulum (ER) is a network of membranous tubules and sacs involved in protein synthesis, lipid metabolism, and calcium storage.
- Both guard cells and other epidermal cells possess endoplasmic reticulum to support these cellular functions.
- Hence, the presence of endoplasmic reticulum does not differentiate guard cells from other epidermal cells.

In Conclusion

Among the given options, the distinguishing characteristic of guard cells in land plants is the presence of chloroplasts. Chloroplasts enable guard cells to perform photosynthesis and regulate stomatal opening and closing, which is vital for the plant's gas exchange and water balance. The other options (cytoskeleton, mitochondria, and endoplasmic reticulum) are not unique to guard cells and are present in various other cell types as well.