Final answer:
Airway resistance primarily originates in the bronchioles of the respiratory tree. Factors such as surface tension, lung compliance, and the presence of pulmonary surfactant can contribute to variations in airway resistance during breathing.
Step-by-step explanation:
The primary location where airway resistance originates in the respiratory tree is in the smaller airways known as bronchioles. These bronchioles have a smaller tubular diameter, causing more collisions between air molecules and the walls of the airways, leading to increased resistance. Additionally, variations in airway resistance during breathing can be influenced by factors such as the presence of surface tension within the alveoli, compliance of the lungs, and the presence of pulmonary surfactant.