Final answer:
Elastic recoil in the lungs is the property that allows the lungs to return to their original size after stretching, facilitating passive expiration by increasing intrapulmonary pressure and moving air out of the lungs.
Step-by-step explanation:
Elastic recoil in the lungs refers to the elasticity of lung tissue that facilitates the lungs to return to their original shape after being stretched or filled with air. This property is crucial for respiration, especially during expiration. When the lungs are filled with air during inspiration, the elastic recoil works to exert pressure back toward the interior of the lungs. During exhalation, the elastic recoil allows the lungs to deflate passively without the need for muscle contraction.
The process of normal expiration is especially dependent on this recoil. The diaphragm and intercostal muscles relax after the phase of inspiration, leading to a decrease in thoracic cavity volume. This decrease causes an increase in the intrapulmonary pressure above atmospheric pressure, generating a pressure gradient that causes air to passively exit the lungs, facilitated by the lung's elastic recoil.
To answer the original question, option (d) Contraction of alveoli; aids expiration is the closest to describing the role of elastic recoil, although the term "contraction" is not technically accurate for describing the passive recoil process. The most precise description of elastic recoil's role is that it aids in expiration.