New York State Emergency Medical Technician (EMT) Practice Exam

In which part of the lungs does respiration occur?

1. Alveoli

2. Trachea

3. Bronchi

4. Capillaries

The correct answer is: Alveoli

Respiration primarily occurs in the alveoli, which are tiny air sacs located at the ends of the respiratory tree in the lungs. Their structure is uniquely designed to facilitate gas exchange. The walls of the alveoli are extremely thin and are surrounded by a network of capillaries, allowing oxygen to diffuse into the bloodstream while carbon dioxide is expelled from the blood into the alveoli to be exhaled. The alveoli provide a large surface area relative to their volume, which is essential for efficient gas exchange. This area is enhanced by the numerous alveoli present in the lungs, which can number in the millions, significantly increasing the overall surface available for oxygen and carbon dioxide transfer. In contrast, other options like the trachea and bronchi are parts of the airway that serve mainly to conduct air into the lungs but do not participate in gas exchange. The capillaries, while important for transporting gases to and from the blood, are not the site where respiration itself occurs but rather support the process by interfacing with the alveoli. Therefore, the alveoli are the fundamental site for respiration, making them the correct answer.