Final answer:
The larynx is the organ that divides the upper respiratory tract from the lower respiratory tract, serving as the transition point where the airway is divided.
Step-by-step explanation:
The dividing point between the upper respiratory tract and the lower respiratory tract is the larynx, commonly known as the voice box. The upper respiratory tract consists of the nasal cavity, pharynx, and larynx, which are responsible for the conduction and preparation of air to be delivered to the lungs by filtering, warming, and humidifying it. Below the larynx starts the lower respiratory tract, which includes the trachea, bronchi, bronchioles, and alveoli, where the gas exchange occurs. The epiglottis plays a crucial role in this division by sealing off the lower respiratory tract during swallowing.