Final answer:
Oxygen is the gas that is diffused out of the leaf through the stomata, which are regulated by guard cells. These cells open and close the stomata to balance gas exchange with water conservation.
Step-by-step explanation:
The gas that is diffused out of the leaf through the stomata is oxygen (O₂). Plants undergo photosynthesis, where they take in carbon dioxide (CO₂) and release oxygen. The stomata, typically found on the underside of leaves, are surrounded by specialized cells known as guard cells. These guard cells are responsible for the opening and closing of the stomata, regulating not only gas exchange but also water balance through transpiration.
Under adequate conditions, guard cells swell and open the stomata to allow gases like oxygen and carbon dioxide to pass through. During water stress or to prevent excessive water loss, these cells will shrink and close the stomata. In essence, the stomata and their guard cells maintain a delicate balance between the need for carbon dioxide for photosynthesis and the avoidance of excessive water loss.