Final answer:
The combining form for the lymphatic tissue at the back of the oral cavity is tonsils.
Step-by-step explanation:
The combining form for the lymphatic tissue at the back of the oral cavity that helps protect the entrance to the respiratory and digestive systems is tonsils.
The tonsils are a collection of lymphatic tissue located at the back of the mouth. They form a protective barrier against pathogens entering the respiratory and digestive systems through the oral cavity.
The tonsils, along with other lymphoid tissues like the adenoids, are part of the mucosa-associated lymphoid tissue (MALT), which helps defend the body against infections.