So inside our lungs, the specialized structure where gas exchange takes place is known as the alveolas. And we have many alveoli in our lung. Now, the alveoli basically looks like a balloon and it could inflate as well as deflate. Now the reason we have residual volume, the reason that we have these air molecules inside our alveoli is to create a pressure so that our balloon, the alveoli valveolis doesn't actually deflate all the way, doesn't actually collapse. Because if all this residual volume, if all that air was actually removed from our alveolis, we would essentially create a vacuum, an absence of air. And when we have an absence of air molecules, we have no internal pressure.