Stomata are the openings in plants that allow gases to pass through. Each stomata is encircled by two guard cells, each of which contains chloroplasts. Each stoma has a respiratory opening, and the process of opening and closing stomata is dependent on the availability of carbs and sugar in the guard cells.Stomata typically open in the mornings as sunlight touches the leaves and close at night. Changes in the turgor of the guard cells are the direct cause. Each guard cell’s inner wall is strong and flexible. The thin outer walls stretch out and press the inner walls into a crescent shape when turgor develops within the two guard cells bordering each stoma. The stoma is now open. When the guard cells lose their turgor, the stoma closes as the elastic inner walls revert to their previous shape.