Massachusetts Comprehensive Assessment System (MCAS) Biology Practice Test

What role does the diaphragm muscle play in the respiratory system?

1. It closes the air passages

2. It expands the chest during inhalation

3. It helps in the expulsion of carbon dioxide

4. It regulates blood flow to the lungs

The correct answer is: It expands the chest during inhalation

The diaphragm muscle plays a crucial role in the respiratory system primarily by facilitating the process of inhalation. When the diaphragm contracts, it moves downward and flattens, which increases the volume of the thoracic cavity. This change in volume creates a lower pressure in the chest compared to atmospheric pressure, allowing air to flow into the lungs. The diaphragm's movement is essential for efficient breathing, as it significantly expands the chest cavity, aiding in the intake of oxygen, which is vital for cellular respiration and overall bodily functions. This contraction is what enables deep breaths, promoting effective gas exchange in the alveoli of the lungs. Other choices do not accurately reflect the role of the diaphragm. Closing air passages is not part of its function; rather, it helps open them during inhalation. While the diaphragm does assist in the expulsion of air during exhalation, its primary action is about expanding the chest for inhalation. Lastly, it does not directly regulate blood flow to the lungs; that is managed by the cardiovascular system.