Answer:
The alveolar walls and capillary walls share a membrane. That's how close they're getting. This allows oxygen and carbon dioxide to readily pass from the respiratory system to the circulation. Oxygen molecules bind to red blood cells as they return to the heart.
Answer:
A
Explanation:
If it's a permeable membrane then it will allow certain molecules in. If it's impermeable then it won't allow molecules in. Therefore it is the deciding feature of whether something can go into the membrane.
