What is the role of the tonsils located in the pharynx?

The tonsils, situated in the pharynx, play a crucial role in the immune system, specifically in the defense against infections. They are composed of lymphoid tissue and act as a first line of defense by trapping pathogens that enter the body through the mouth and nose. When these pathogens are detected, the tonsils produce antibodies and other immune responses to help fight off infections. This function is particularly important during childhood when the immune system is still developing.

The other options do not align with the primary biological functions of the tonsils. While sound production is associated with the larynx, digestion involves the gastrointestinal tract, and airflow regulation is primarily managed by other structures within the respiratory system. Thus, the tonsils are specifically designated to aid in defense against infection, making that the correct answer.