The composition of inhaled and exhaled air are compared and the anatomy of the respiratory surface is described. Using an animation, the presenters describe how gaseous exchange takes place. The function and importance of the alveoli are explained: large surface area, moist, thin walls, good blood supply.

First broadcast:
21 November 2008

Students could be provided with a list of focus questions to answer during this clip, including an incomplete table comparing inhaled and exhaled air, labelling a diagram of the respiratory system, the direction of movement of carbon dioxide and oxygen, and the adaptations of alveoli.