Guard cells contain chloroplasts and hence can perform photosynthesis. while the epidermal cells do not contain chloroplasts.

The guard cells in land plants differ from other epidermal cells in having chloroplasts. This unique feature allows the guard cells to perform a specialized function in regulating the opening and closing of stomata, which are small pores on the surface of leaves and stems.

Chloroplasts in Guard Cells:
- Chloroplasts are specialized organelles found in the cells of plants and some other organisms. They are responsible for photosynthesis, the process by which plants convert sunlight into energy-rich molecules.
- Guard cells contain chloroplasts, which enable them to produce energy through photosynthesis. This energy is crucial for the active transport of ions and water across the cell membrane, allowing the guard cells to change shape and control stomatal opening and closing.

Stomatal Opening and Closing:
- Stomata play a vital role in plant physiology as they regulate gas exchange, water loss, and the uptake of carbon dioxide for photosynthesis.
- The opening and closing of stomata are controlled by the turgor pressure in the guard cells. When the guard cells take up water, they become turgid and swell, causing the stomata to open. Conversely, when they lose water, they become flaccid, leading to stomatal closure.
- The presence of chloroplasts in guard cells allows them to actively transport potassium ions (K+) into the cell. This increases the osmotic potential inside the cell, causing water to enter and the guard cells to swell. As a result, the stomata open, allowing gas exchange and water vapor loss.

Photosynthesis in Guard Cells:
- The chloroplasts in guard cells also enable them to carry out photosynthesis. During this process, light energy is absorbed by the chlorophyll pigment in the chloroplasts, and carbon dioxide from the surrounding air is converted into glucose.
- The photosynthetic activity in guard cells produces ATP (adenosine triphosphate), which is the energy currency of cells. This ATP is utilized for active ion transport, such as pumping in potassium ions, which leads to stomatal opening.

In conclusion, the presence of chloroplasts in guard cells is essential for their unique function in regulating stomatal opening and closing. The chloroplasts allow the guard cells to perform photosynthesis and produce energy-rich molecules, which is crucial for active ion transport and controlling the turgor pressure necessary for stomatal movement.