The cartilage prevents the trachea collapsing when the air pressure inside it is lowered during inspiration. The goblet cells produce the mucus that traps particles from inhaled air, while the cilia move the mucus laden with dirt and microorganisms up the throat, where it passes into the stomach, via the esophagus.
Protect the alveoli from damage by having mucus that traps dirt, and cilia that move this dirt mucus away from the alveoli.
The muscle allows them to constrict, and to control the flow of air in and out of the alveoli
The elastic fibres allow the alveoli to stretch as they are filled with air during inhalation and then recoil during exhalation in order to expel the carbon dioxide-enriched air. The collagen fibres add strength to the thin-walled alveoli and so prevent them from bursting during inhalation