Oxygen molecules that are in a higher concentration outside the cell will diffuse from an area of higher concentration (outside the cell) to an area of lower concentration (inside the cell). (D). It is a rule that liquids and gases move from an area of high concentration into an area of low concentration. This is called Osmosis. The cell wall is a semi-permeable membrane which also acts as a filter to stop foreign and unwanted molecules from passing in and out of the cell.