Final answer:
The differences between the trachea, bronchus, and alveolus are highlighted by the presence of cartilage rings in the trachea, smooth muscle in the bronchus, and thin walls in the alveolus, facilitating the respective functions of these parts in the respiratory system.
Step-by-step explanation:
The correct answer to the question about the differences in structures found in the trachea, bronchus, and alveolus is option b) Trachea has cartilage rings, bronchus has smooth muscle, alveolus has thin walls. The trachea is composed of stacked, C-shaped pieces of hyaline cartilage. It has a fibroelastic membrane and trachealis muscle that allows it to stretch and contract while preventing collapse. The bronchus, like the trachea, initially contains cartilage as structural support but also contains smooth muscle that is innervated by the parasympathetic and sympathetic nervous systems which control the muscle for constriction and dilation. As the airways divide into smaller bronchioles, the cartilage is replaced with elastic fibers. Finally, at the end of the airway tree lie the alveoli, which are thin-walled sacs surrounded by capillaries where gas exchange takes place. The thin-walled structure of alveoli and their direct contact with capillaries enable efficient diffusion of oxygen and carbon dioxide between the lungs and the blood.