what can pass through a membrane
Water diffusion is called osmosis. Oxygen is a small molecule and itâs nonpolar, so it easily passes through a cell membrane. Carbon dioxide, the byproduct of cell respiration, is small enough to readily diffuse out of a cell. Small uncharged lipid molecules can pass through the lipid innards of the membrane. Larger or charged molecules might be able to slowly diffuse across the membrane. The charge on a molecule might help or hinder its diffusion, based on the relative charges on either side of the membrane.