The purpose of the cell membrane is to hold the different components of the cell together and to protect it from the environment outside the cell. The cell membrane also regulates what enters and exits the cell so that it doesn’t lose too many nutrients, or take in too many ions. It also does a pretty good job of keeping harmful things out.Ions and large polar molecules cannot pass through the lipid bilayer. But more specifically, whether a molecule can pass through the membrane depends on its size and its electrical nature. The membrane is highly permeable to non-polar (fat-soluble) molecule.
