Air enters your body through your nose, then enters the pharynx through the two nasal passages. Then it passes into the larynx and then into the trachea though an opening called glottis. The trachea divides into two bronchi (one for each lung), and further branches into numerous bronchioles. At the end of each bronchiole, there is a cluster of air sacs called alveoli. It is inside the alveoli that gas exchange actually takes place.
All of the above mentioned organs aid respiration as it is through them that oxygen-rich air enters the body, and then the oxygen enters our bloodstream in the lungs. Oxygen is used in aerobic respiration, a process in which energy is released from the food that we have eaten.