Is the trachea a part of the digestive or the respiratory system?
The trachea is a tube/windpipe in the respiratory system and it connects it to the mouth, nose and the lungs. It's main function is to transport the air the person inhales through it's nose or mouth into the mouth, without the trachea the lungs would not receive oxygen and us humans wouldn't survive.
You can read further information on the respiratory system and its parts and the functions here http://www.innerbody.com/anatomy/respiratory#full-description
Hope this helps!