Answer:
hey Ash!!!
Explanation:
the answer is CO2.
Guard cells are specialized cells inthe epidermis of leaves, stems and others organs that are used to control gas exchange, including water vapor via transpiration. Guard cells perceive and process environmental stimuli to trigger cellular responses resulting in stomatal opening or closure. All but one envionmental stimuli might trigger stomatal opening.
Guard cells are cells surrounding each stoma. They help to regulate the rate of transpiration by opening and closing the stomata. To understand how they function, study the following figures. As you look at the figures, keep in mind that an increase in solute concentration lowers the water potential of the solution, and that water moves from a region with higher water potential to a region of lower water potential.
Notice that in figure A the guard cells are turgid, or swollen, and the stomatal opening is large. This turgidity is caused by the accumulation of K+ (potassium ions) in the guard cells. As K+ levels increase in the guard cells, the water potential of the guard cells drops, and water enters the guard cells.
In figure B, the guard cells have lost water, which causes the cells to become flaccid and the stomatal opening to close. This may occur when the plant has lost an excessive amount of water. In addition, it generally occurs daily as light levels drop and the use of CO2 in photosynthesis decreases.
