Stomata open and close in response to -

Responses

water being pumped in and out of guard cells
water being pumped in and out of guard cells, EndFragment,

crystal formation in the plant due to excess glucose.

, crystal formation in the plant due to excess glucose.,

the lack of available sunlight during the night
the lack of available sunlight during the night, EndFragment,

stimulation by auxins producing rapid growth
stimulation by auxins producing rapid growth, EndFragment,

changes in temperature and humidity levels

changes in CO2 levels in the surrounding environment