Final answer:
Approximately 6,500 terminal bronchioles arise from each tertiary bronchus, leading to the respiratory zone in the lungs where gas exchange occurs.
Step-by-step explanation:
Roughly 6,500 terminal bronchioles arise from each tertiary bronchus. The bronchioles further branch until they become the tiny terminal bronchioles, which lead to the structures of gas exchange.
The walls of bronchioles are muscular and can adjust the airflow through them but do not contain cartilage like the bronchi. The terminal bronchioles then give way to a network of respiratory bronchioles, which are further connected to alveolar ducts and alveolar sacs where the gas exchange occurs.
Respiratory Zone is a critical part of the lungs because it comprises the alveolar ducts and alveoli where the exchange of oxygen and carbon dioxide takes place. Therefore, the correct answer to the question is: 'b.6500' terminal bronchioles from each tertiary bronchus.