Red blood cells transport oxygen for tissues and cells through several membranes, and oxygen enters the human body from these membranes (preferably which layers). Thank God for his help.

Monolayer cells in alveolar wall: passing through two layers of cells that need to go in and out; Monolayer cells of capillary wall: passing through two layers of cells that need to enter and exit; Oxygen needs to be transported by red blood cells: it enters the 1 layer of red blood cells; No longer passes through the membrane during transportation; Arrival destination: layer1; Monolayer cells pass through the capillary wall: through two layers of cells that need to go in and out; Into the tissue cells: 1 layer. At this point, the answer to your question came out: **9 floors. Note that this only refers to entering the tissue cells, but if you ask the tissue cells to participate in aerobic respiration, you should add two mitochondrial membranes: two, *** 1 1, and check the questions by yourself.