Final answer:
An alveolus is a tiny air sac at the end of the respiratory tract, found in clusters within the lungs, where oxygen and carbon dioxide are exchanged between the air and the blood. The correct definition for the term alveolus is B) tiny air sac that is the terminal element of the respiratory tract.
Step-by-step explanation:
The correct definition for the term alveolus is B) tiny air sac that is the terminal element of the respiratory tract.
An alveolus is the end region of the lung where gas exchange occurs. Air arrives at the alveoli after traveling through the respiratory system via the nasal cavity, pharynx, larynx, trachea, bronchi, and bronchioles. Alveolar ducts are small tubes that lead to clusters of alveoli, where oxygen diffuses into the blood and carbon dioxide diffuses out to be exhaled. Each alveolar sac can contain up to 30 alveoli, each resembling tiny bubbles. The alveoli, with their thin walls, closely contact the capillaries, enabling efficient gas exchange. This exchange is vital for oxygenating the blood and removing waste gases from the body. The surface area of the alveoli in the lungs is estimated to be as large as 100 m², which is roughly the size of half a tennis court, allowing for extensive gas diffusion.