9. Very fine hairs called cilia cover the inner surface of your nose. How do the fine hairs help to collect dust, bacteria, and mucus, and keep the nasal passages clean? 10. In each lung, the small tubes that branch off the bronchi are called 11. The alveoli, air sacs in the lungs, contain a network of tiny blood vessels and capillaries. What is transferred through the walls of the alveoli into the bloodstream? 12. Match the word to the meaning: Answers: Word: 1. exhalation 2. inhalation 3. carbon dioxide Meaning: A. Breathing in B. The air that is breathed out of the lungs C. Breathing out 13. Why is it easier to breathe at sea level than at higher altitudes? 14. Name three ways you can help keep your respiratory system healthy. 1. 2. 3.​