Question

For oxygen to move from the alveoli onto a hemoglobin molecule in the blood, what are the structures it would need to cross (in order)?

A. Alveolar epithelial cell, basement membrane, capillary epithelial cell, and red blood cell plasma membrane.
B. Red blood cell plasma membrane, capillary epithelial cell, basement membrane, and alveolar epithelial cell.
C. Alveolar epithelial cell, capillary epithelial cell, basement membrane, and red blood cell plasma membrane.
D. Basement membrane, alveolar epithelial cell, capillary epithelial cell, and red blood cell plasma membrane.

Answer 1

Oxygen moves from the alveoli onto a haemoglobin molecule in the blood by crossing the alveolar epithelial cell, followed by the basement membrane, then the capillary endothelial cell, and finally the red blood cell plasma membrane. The correct order is represented by Option A among the given ones.

Step-by-step explanation:

For oxygen to move from the alveoli onto a haemoglobin molecule in the blood, the sequence of structures it needs to cross, in order, are the alveolar epithelial cell, basement membrane, capillary endothelial cell, and the red blood cell plasma membrane. Therefore, the correct answer to the question is A which mentions Alveolar epithelial cell, basement membrane, capillary epithelial cell, and red blood cell plasma membrane.

During external respiration, oxygen first diffuses through the thin squamous epithelium formed by type I alveolar cells. It then passes the basement membrane, which supports the epithelial layer. Next, oxygen goes through the capillary endothelial cell, which forms the wall of the pulmonary capillaries. Finally, oxygen crosses the red blood cell plasma membrane and binds to the metalloprotein haemoglobin inside the red blood cells (RBCs). The oxygen is then carried to body tissues, where it is released to meet the metabolic demands of the cells.