Diffusion occurs in the lungs of the body in the alveoli. Oxygen diffuses from the alveoli of the lungs into the small capillaries that surround them and carbon dioxide diffus … es in the opposite direction; this is called gaseous exchange and it happens to oxygenate and get rid of the waste carbon dioide.smosis is the diffusion of water across a semi-permeable (or differentially permeable or selectively permeable) membrane. The cell membrane, along with such things as dialysis tubing and cellulose acetate sausage casing, is such a membrane. The presence of a solute decreases the water potential of a substance.