1. The lungs

4. Use all of these words to explain how the lungs work: Lungs Trachea Bronchi Bronchioles Alveoli (alveolus) Blood capillaries Now answer all the questions on page 47.

5. Breathing Is when muscles change the size of your lungs. When you inhale your lungs get bigger. When you exhale your lungs get smaller. The movement of air into and out of your lungs is called ventilation.

7. Gas exchange Picking up oxygen and getting rid of carbon dioxide in the alveoli is called gas exchange. Red blood cells are bright red when carrying oxygen and dark red/brown when not. The lungs contain thousand of air sacs containing tiny pockets called alveoli.

8. Alveoli Give the lungs a large surface area. The walls are only 1 cell thick. They are surrounded by many blood capillaries. The thins walls of both speed up diffusion of substances (oxygen, carbon dioxide, glucose).