In order for an oxygen molecule to enter the blood from the lungs it must first cross the ____.
A)hemoglobin
B)red blood cell membrane
C)capillary endothelium
D)fluid basement membrane
E)alveolar epithelium

Question

In order for an oxygen molecule to enter the blood from the lungs it must first cross the ____. ​
A)hemoglobin ​
B)red blood cell membrane
C)capillary endothelium
D)fluid basement membrane
E)alveolar epithelium ​

Quizplus · Accepted Answer

Oxygen must cross from the air in the alveoli of the lungs to the bloodstream, which is contained within capillaries that lie directly adjacent to the alveolar epithelium. The oxygen must diffuse across the capillary endothelium to enter the bloodstream. Hemoglobin is a protein found within red blood cells that binds to oxygen in the bloodstream. The red blood cell membrane and fluid basement membrane do not directly separate the alveoli from the bloodstream.

In Order for an Oxygen Molecule to Enter the Blood