Guard Cells
Guard cells are specialized cells found in the epidermis of plant leaves and stems. They play a crucial role in regulating the opening and closing of stomata, which are tiny pores on the leaf surface that allow for gas exchange.

Plasmodesmata Presence
The correct statement among the given options is that plasmodesmata are absent in guard cells (option D). Plasmodesmata are channels that connect adjacent plant cells and allow for the transport of nutrients, signals, and other molecules between cells. However, guard cells have a unique structure and function that necessitates the absence of plasmodesmata.

Regulation of Stomatal Aperture
Guard cells control the opening and closing of stomata to regulate gas exchange and water loss in plants. When the guard cells become turgid, they swell and create an opening between them, allowing for the exchange of gases and water vapor. In contrast, when the guard cells lose turgidity, they become flaccid, closing the stomatal pore.

Structural Features of Guard Cells
Guard cells have several structural features that enable their specialized function in stomatal regulation. These features include:

1. Thick Cell Walls: Guard cells have thicker cell walls compared to surrounding epidermal cells. This added thickness provides structural support and helps maintain the shape and integrity of the guard cells.

2. Presence of Mitochondria: Contrary to option A, guard cells do have mitochondria. Mitochondria are essential organelles responsible for energy production through cellular respiration. Guard cells require energy to actively transport ions and water, which is essential for their turgidity changes and stomatal regulation.

3. Presence of Vacuoles: Option C states that guard cells are devoid of vacuoles, which is incorrect. Guard cells contain large central vacuoles, which play a crucial role in controlling their turgidity. When the vacuoles accumulate water, the guard cells become turgid and open the stomata.

4. Absence of Plasmodesmata: Option D is the correct statement. Guard cells lack plasmodesmata, which restricts the movement of molecules and ions between adjacent cells. This feature allows guard cells to independently regulate their turgor pressure and respond quickly to environmental cues.

In summary, guard cells have thick cell walls, contain vacuoles, and have mitochondria. However, they lack plasmodesmata, which allows for their independent regulation and control of stomatal aperture.