The air spaces in the spongy mesophyll of a leaf connect with the exterior of the leaf through stomata. Stomata are small, pore-like structures found on the surface of leaves that allow for the exchange of gases between the leaf and the atmosphere.

When stomata are open, air can enter the leaf and diffuse into the intercellular spaces of the spongy mesophyll. These air spaces are connected to the xylem and phloem vessels that transport water and nutrients throughout the leaf. The air spaces also provide a pathway for the diffusion of carbon dioxide and oxygen, which are essential for photosynthesis and respiration, respectively.

The opening and closing of stomata is controlled by guard cells, which are specialized cells that surround the stoma. When the guard cells are turgid, the stoma is open, and when the guard cells are flaccid, the stoma is closed. The turgidity of the guard cells is regulated by several factors, including the concentration of carbon dioxide in the atmosphere, the light intensity, and the water status of the leaf.