Final answer:
The respiratory membrane consists of the alveolar epithelium and the endothelium of the surrounding capillaries. It enables the exchange of gases between the air in the alveoli and the blood.
Step-by-step explanation:
The respiratory membrane consists of the alveolar epithelium (simple squamous epithelium in the alveoli) and the endothelium of the surrounding capillaries. These two layers together form a respiratory membrane that is approximately 0.5 micrometers thick. The respiratory membrane allows gases to cross through it by simple diffusion, enabling the exchange of oxygen and carbon dioxide between the air in the alveoli and the blood in the capillaries.