The immediate cause of the opening and closing

Options

A. Turgidity change of guard cells
B. Flaccidity of guard cell
C. Orientation of microfibrills
D. Turgidity of subsidiary cells

Answer

**Step-by-Step Solution:**

1. **Understanding Guard Cells:**
- Guard cells are specialized cells that surround the stomata (pores) on the surface of leaves. Their primary function is to regulate the opening and closing of these stomata, which controls gas exchange and transpiration in plants.

2. **Water Entry and Turgidity:**
- The immediate cause of the opening of guard cells is the entry of water. When water enters the guard cells, they become turgid (swollen due to water uptake). This turgidity is crucial for the functioning of guard cells.

3. **Mechanism of Opening:**
- As the guard cells become turgid, the thin outer walls of the guard cells are pushed outward. This occurs because the water pressure inside the cells increases, causing them to expand.

4. **Movement of the Inner Wall:**
- The inner wall of the guard cells is thicker and does not stretch as easily. As the outer walls are pushed out, the inner walls are pulled inward, which results in the opening of the stomata.

5. **Flaccidity and Closing:**
- When water leaves the guard cells (due to factors like low humidity or high temperatures), the cells become flaccid (less turgid). This causes the stomata to close as the outer walls are no longer pushed outward and the inner walls are not pulled as much.

6. **Conclusion:**
- Therefore, the immediate cause of the opening and closing of guard cells is the change in turgidity of the guard cells due to water movement. The correct answer to the question is option A: "due to turgidity of guard cells."