The respiration surface in humans is the alveoli. It is adapted to its function as a gas exchange surface because it has a high surface area to volume ratio, this allows maximum surface area for gas exchange to take place, increasing the efficiency. The alveoli are covered in a layer of moisture, which allows gases to diffuse across the surface. Alveoli are one cell thick which means that gases have a minimal distance to travel from the lungs into the capillaries. The alveoli have a good blood supply as they are surrounded by capillaries.