Describe/ explain mechanisms/ theories of opening and closing of stomata/ describe how the presence of chloroplasts in the guard cells affect opening and closing of stomata.

A.Photosynthetic theory.
.Opening of the stomata.
-Chloroplast are sites for photosynthesis; during the day photosynthesis takes place; producing glucose; glucose being osmotically active increases the osmotic pressure of the guard cells; water is drawn into the guard cells (from adjacent epidermal cells); the guard cells become turgid; bulging outwards opening the stomata;
.Closing of the stomata.
-At night photosynthesis does not take place; sugar/ glucose is converted to starch; Starch is osmotically inactive hence lowers the osmotic pressure of the guard cells; and the cells lose water to the adjacent epidermal cells through osmosis; The guard cells lose turgidity; and become plasmolysed leading to closure of stomata;
B.pH/ Starch-sugar interconversion theory.
.Opening of stomata.
-During the day photosynthesis takes place; using carbon (IV) oxide making the pH to rise/ lower acidity in the guard cells favoring the conversion of starch into glucose; glucose being osmotically active increases the osmotic pressure of the guard cells; water is drawn into the guard cells (from adjacent epidermal cells); the guard cells become turgid; bulging outwards opening the stomata;
.Closing of stomata
-At night photosynthesis does not take place hence carbon (IV) oxide is not used; Carbon (IV) oxide accumulates in the guard cells lowering the pH/ increasing acidity; favoring the conversion of glucose into starch; Starch is osmotically inactive hence lowers the osmotic pressure of the guard cells; and the cells lose water to the adjacent epidermal cells through osmosis; The guard cells lose turgidity; and become plasmolysed leading to closure of stomata;
C.Potassium ion/ Active transport theory.
.Opening of stomata.
 During the day photosynthesis takes place; ATP accumulates in the guard cells making the guard cells to draw potassium ions (from surrounding epidermal cells); the osmotic pressure increases in the guard cells; water is drawn into the guard cells; making them turgid; bulging outwards opening the stomata;
.Closing of stomata.
-At night photosynthesis does not take place; the number of ATP molecules falls rapidly; Potassium ions diffuse from the guard cells to adjacent epidermal; This lowers the osmotic pressure of the guard cells; hence they lose water to the adjacent epidermal cells through osmosis; The guard cells become plasmolyzed and the stomata close;