From the time when oxygen enters the human body (preferably which layers), red blood cells transport oxygen through several layers of membranes for use by tissues and cells.

Oxygen enters the alveoli from the lungs: it passes through the second layer of alveolar cells.

Enter the capillary: pass through the capillary wall (one layer of epithelial cells, two layers of membranes) and enter 1 layer of red blood cells (oxygen is carried by hemoglobin).

Arriving at tissue cells: passing through 1 layer of red blood cells and passing through 2 layers of capillary wall cells.

Entering tissue cells: passing through the 1 layer of tissue cell membrane and entering the second layer of mitochondria (double membrane structure of mitochondrial membrane).

To sum up, it has to go through 1 1 layered membrane structure.