Lungs do not collapse between breaths and some air always remains in the lungs which can never be expelled because

Options

A. there is a negative pressure in the lungs
B. there is an negative intrapleural pressure pulling at the lung walls
C. there is a positive intrapleural pressure
D. pressure in the lungs in higher than the atomospheric pressure

Answer

B

Explanation

Lungs do not collapse between breaths and some air always remains in the lungs which can be never expelled because there is a negativbe intrapleural pressure pulling at the lung walls. Alveoli are basic functional unit of lungs.The outer alveolar wall surface has cells which secrete DPPC also called as lipid surfctant
The surfactant expands the alveoili diue to which the negative pressure inside the alveloi increases .This prevents the alveloi from collapsing.Since in this questioon both options (a) and (b) are correct and option (b) provdes more appropriate explanation therefore it must be chosen