The respiratory system is primarily used to transport air, while the digestive system is used to transport fluids (such as water) and solids (such as food particulates). The respiratory and the digestive systems share the region of the mouth and upper throat, where air, fluids, and solids can be mixed. This region is known as the pharynx, and is the correct answer.

The larynx is a region located below the pharynx and is the area in which the tract divides into the respiratory tract and digestive tract. Solids and liquids are transported through the esophagus and into the stomach, while air enters the trachea to be transported to the lungs via the bronchi. The epiglottis is a cartilage flap that prevents solids and liquids from entering the trachea. The vocal cords are located in the respiratory tract only.

The larynx is considered to be the "voice box" and contains the vocal cords. Speech is created by vibrations in the flaps that make up the vocal cords.

Other parts of the respiratory system include the trachea and bronchus, which both help to transport air to the lungs. The epiglottis is a flap attached to the entrance of the larynx in order to prevent foreign objects, such as food or water, from entering. The uvula hangs from the posterior edge of the middle of the soft palate.

The trachea divides into two when it enters the lungs, a process known as bifurcation. The result is the two pathways known as the prinary bronchi. The bronchi continue to branch into more and more bronchioles throughout the lungs.

The nasal mucosa helps warm incoming air. The trachea becomes thinner when it enters the lungs, as opposed to wider and thicker. Alveoli are responsible for absorbing oxygen; oxygen cannot be absorbed by neighboring capillaries in the trachea or bronchi.

The trachea bifurcates (splits in two) to create the left and right bronchi upon entering the lungs.

Bronchioles arise from the subsequent branching of the bronchi, and eventually send oxygenated air to the alveoli for gas exchange with deoxygenated blood via adjacent capillary beds. The esophagus is used to transport food and liquids from the mouth to the stomach, and is not involved in the respiratory system or lungs.

The larynx contains the vocal cords and conducts air from the pharynx to the trachea.

The pharynx is the region of the back of the mouth/nose and upper throat. The trachea conducts air between the larynx and the bronchi. The bronchi conduct air from the trachea to the lungs. The epiglottis is a flap of cartilage in the pharynx that covers the opening to the larynx during swallowing and directs food and liquids down the esophagus. 

The mouth and pharynx are the first two structures air travels through during inspiration, or inhalation, in the respiratory system. The pharynx is located at the back of the mouth, and is the upper region of the throat that connects the nose and mouth.
Although there is a tendency to confuse the trachea and the esophagus, students should understand the fundamental difference. The trachea is a respiratory structure, which transports air and gases between the external atmosphere and the internal environment of the lungs. The esophagus is a digestive system structure, which, through the muscular contractions of peristalsis, carries ingested food down to the stomach. Thus, esophagus is the correct answer. 

The process of air moving into and out of the lungs is called pulmonary ventilation. Cellular respiration refers to the process by which fuel molecules are converted into energy molecules such as ATP (think back to glycolysis, Krebs cycle, and electron transport). Pulmonary respiration refers to the specific process of gas exchange between the body (capillaries) and the environment (air inside the alveoli).

Aleveoli are small sacs in the lungs which help with the exchange of carbon dioxide and oxygen from the bloodstream to the lungs. The trachea and bronchi are surrounded by thick connective tissue (cartilage) and thus, their walls are much too thick to allow gas exchange, thus they function to transport air to and from the alveoli. The pleura are the membranes surrounding the lungs and lining the thoracic wall, and thus never come into direct contact with air. The thorax is not a part of the lungs, rather, it is the anatomical region we commonly refer to as the chest.

Alveoli, like most bodily structures, are part of an aqueous environment, making them subject to the surface tension of water. Surfactant lowers surface tension, allowing the alveoli to expand with much less pressure than they would against full surface tension. As a result, inspiration of air requires less effort, making it more energetically efficient. 

The respiratory system is composed of the mouth, trachea, bronchi, bronchioles, and alveoli in the lungs. The primary function of the system is to bring air to the alveoli, where it can interact with blood in nearby capillaries. Oxygen diffuses into the blood from the alveoli, while carbon dioxide is transferred out of the blood, in a process known as gas exchange.

While the respiratory system is responsible for re-oxygenating blood, it is the circulatory system that actually delivers the oxygen to the tissues of the body. The immune system battles foreign pathogens, and the excretory system maintains fluid balance.