What is the requirement for inspiration to occur?

Step-by-step solution

Breathing involves two stages : inspiration during which atmospheric air is drawn in and expiration by which the alveolar air is released out . The movement of air into and out of the lungs is carried out by creating a pressure gradient between the lungs and the atmosphere. Inspiration can occur if the pressure within the lungs (intra-pulmonary pressure) is less than the atmospheric pressure, i.e., there is a negative pressure in the lungs with respect to atmospheric pressure . Similarly, expiration takes place whe