Final answer:
Bronchi contain cartilage for structural support and smooth muscle, while bronchioles lack cartilage and have a greater amount of smooth muscle, allowing for adjustable air passage diameters through muscle contraction and relaxation.
Step-by-step explanation:
The significant structural differences between bronchi and bronchioles involve the presence of cartilage and the muscle dynamics that regulate airflow. Bronchi have supporting cartilage and smooth muscle, while bronchioles have no cartilage and more smooth muscle relative to their size. In contrast, bronchi are larger passages beginning from the trachea that include primary, secondary, and tertiary bronchi before tapering into bronchioles.
The absence of cartilage in bronchioles allows their diameter to change significantly, providing a mechanism to increase or decrease airflow, which is not possible in the more rigid bronchi. In summary, bronchi are made up of cartilage and muscle allowing for a stable passageway for air, while bronchioles, lacking cartilage, have a higher concentration of muscle to enable dynamic control of air resistance and distribution within the lungs.