Answer:
The answer is 2.
Step-by-step explanation:
When oxygen gets into the lungs, it first needs to diffuse through the alveoli and into the blood. Then through the veins and capillaries, it diffuses into all the calls in the body. It does so quite easily because it is a nonpolar and a very small molecule with a low concentration inside the cell. This gives it the ability to diffuse easily through the cell membrane.
So the number of times that oxygen has to diffuse through a plasma membrane is two.
I hope this answer helps.