Opening and closing of stomatal pore depends on:
(A) Atmospheric temperature
(B) oxygen concentration around stomata
(C) carbon dioxide concentration around stomata
(D) water content in the guard cells
The guard cells of the stomata swell when water flows into them , causing the stomatal pore to open. Similarly the pore closes if the guard cells shrink.
Thus, opening and and closing of stomatal pore depends on water content in the guard cells
So, the correct answer is (d)