What is one critical feature of mammalian respiration?

The correct choice highlights the fundamental process of mammalian respiration, which relies on negative pressure to facilitate breathing. In mammals, the diaphragm and intercostal muscles create a difference in pressure between the lungs and the external atmosphere. When the diaphragm contracts, it increases the thoracic cavity's volume, decreasing the internal pressure within the lungs compared to that of the external environment. This negative pressure gradient allows air to flow into the lungs during inhalation.

Negative pressure ventilation is vital because it enables efficient gas exchange; the lungs can fill with air, bringing in oxygen and allowing carbon dioxide to be expelled during exhalation. This process is distinct from positive pressure methods, where air is pushed into the lungs, which is not the primary mechanism for mammals. Additionally, mammals do not use gills for respiration, as that mechanism is typical of aquatic organisms, nor do they utilize tracheal ventilation, which is characteristic of insects. Thus, negative pressure plays an essential role in ensuring proper respiration and overall respiratory health in mammals.