Mechanism of stomatal opening and factors that influence stomatal opening

Question 1

When do stomata open and close

Answer 1

The stomata of most species tend to open in the light and close in the dark

Question 2

What happens when the stomata are in the light

Answer 2

In the light, potassium ions are actively accumulated in the guard cells, thus the water potential is more negative within the guard cells. Water from other cells enters the guard cells by osmosis through the selectively permeable cell membrane. The turgor pressure inside the guard cells increase. Thus, it becomes turgid, and the stomata opens

Question 3

What happens when the stomata is in the dark

Answer 3

In darkness, potassium ions leave the guard cells, thus the water potential in the guard cells become less negative. Water leabes the guard cells by osmosis across the selectively permeable cell membrane. Turgor pressure inside the guard cells decreases. Thus, the guard cells straighten up and close the stomatal pore.

Question 4

Why do the cells increase more in length than width when turgor increases

Answer 4

The cell wall next to the stomatal pore is thicker than that further away from the pore. Cellulose microfibrils in the walls resists stretching and compression. Thus, the radial orientation of the microfibrils causes the cells to increase in length more than width when turgor increases. The two guard cells are attached at their tips, so the increase in length causes buckling