Which of the following structures is not a part of the respiratory system?
a. external nares
b. uvula
c. epiglottis
d. choanae
e. mouth

Uvula.

Explanation:

Respiration may be defined as the process of exchange of gases between the body tissue, lungs and the environment. Oxygen is inhaled and carbon dioxide is exhaled out during the process of respiration.

The choanae, external nares, epiglottis and mouth plays an important role in respiration. Uvula is mainly involved in the production of the salivary gland. The uvula moistens the area and also involved in the speech process. Hence, uvula do not play important role in respiration.

Thus, the correct answer is option (b).

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