Final answer:
The epiglottis is the structure that closes off the tracheal opening, preventing food and liquid from entering the airway during swallowing.
Step-by-step explanation:
When swallowing occurs, the structure that occludes the tracheal opening to prevent aspiration of food and liquid is the epiglottis. The epiglottis is a flap made of elastic cartilage at the root of the tongue that is crucial for preventing food and liquid from entering the windpipe (trachea) and causing choking. During swallowing, as the soft palate and uvula close off the nasopharynx and the larynx is pulled up, the epiglottis folds down, sealing the glottis (the opening of the larynx) and guiding the swallowed contents into the esophagus instead of the respiratory tract. If food does mistakenly enter the larynx, it triggers a cough reflex to expel the food from the respiratory tract.