The given graph shows changes in the air pressure of lungs during breathing. What causes the change in air pressure during period X?

Options

A. Contraction of the diaphragm muscles
B. Decrease in the volume of the lungs
C. Movement of ribs downward and inward
D. Relaxation of the external intercostal muscles

Answer

A

Explanation

Contraction of the diaphragm muscles make it flat and contraction of the external intercostal muscles causes upward and outward movement of ribcage, thus increasing the volume of lungs. As the volume increases, the pressure inside the lungs decreases (as shown by the part .X. of the graph). This will cause the air from outside to rush inside the lungs, causing inspiration.