What divides the left and right side of the nasal cavity?

The structure that divides the left and right side of the nasal cavity is the septum. The nasal septum is made up of both bone and cartilage and serves as a partition separating the two nasal passages. This anatomical feature plays a crucial role in the normal functioning of the respiratory system, as it helps to direct airflow and filter the air entering the lungs.

In contrast, the conchae are bony structures located within the nasal cavity that assist in regulating airflow and warming humid air but do not divide the cavity. The pharynx is a part of the throat that connects the nasal cavity to the esophagus and is not a dividing structure of the nasal cavity. The sinus refers to the air-filled spaces around the nasal cavity and does not play a role in dividing the nasal cavity itself. Thus, the nasal septum is the correct and specific answer for this question as it distinctly separates the left and right sides.