Final answer:
The respiratory system employs cilia and mucus to filter out particles, which together form the mucociliary escalator, and uses the epiglottis to prevent food from entering the airways while swallowing. so, option a is the correct answer.
Step-by-step explanation:
The respiratory system filters out particles and keeps food from entering the airways primarily through the action of cilia and mucus. The cilia are hair-like structures that line the respiratory tract and move rhythmically to transport mucus, along with trapped particles and pathogens, towards the throat where it can be swallowed and sent to the stomach to be destroyed by stomach acids. This process is known as the mucociliary escalator.
In the nasal cavity, as air is inhaled, it is filtered by hairs and mucus which trap dust, dirt, and other particulates. This mucus is constantly moved along by the cilia, ensuring that filtered out materials are expelled from the body either through coughing or swallowing, a process which also aids in keeping food out of the respiratory system during normal breathing and swallowing.
Protective Mechanisms of the Respiratory System
Aside from the mucociliary escalator, the body has other protective mechanisms to prevent food from entering the respiratory system. The epiglottis, a flap of tissue, plays a crucial role by covering the opening to the airways during swallowing, ensuring food is directed towards the esophagus and away from the lungs.