The document discusses the lungs and respiration. It notes that the rib cage expands while the lungs tend to collapse. This creates contradictory movements that enable inspiration. The lungs contain around 300 million alveoli to increase surface area for gas exchange. Alveolar cells are of two types - type I forms walls while type II produces surfactant.

1. AP15 aim: how do contradictory movements of the lungs enable inspiration?