Physical and chemical barriers that form the body's first line of defense against pathogens include

They include the skin as the first physical barrier. Another physical barrier is the cilia in the nasopharynx that beat to remove any foreing material towards the outside of the nose. Mucus traps the foreign materials. Chemical barriers include the low ph level on the skin, due to its secretions, and in the stomach due to production of grastric juices and tears in the eyes that have lysozymes.

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Competition. interaction among organisms that compete for the same natural resource (food, shelter, water, space) in an ecosystem. predation. an interaction in which one organism kills another for food. predator. prey. symbiosis. mutualisum. commensalisum. parasitisum.

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