The cell membrane is a barrier to the entry and exit of substances. They are semi-permeable barriers, allowing some substances through but not others. It does this by having some small pores or channels.
The membrane is a thin sheet composed of a lipid (fat) bilayer called phospholipid. It consists of a water-soluble end (hydophilic), facing inwards to the cytoplasm and outwards to the extracellular fluid. The non-water-soluble (hydrophobic) ends face each other internally. The lipid bilayer is embedded with protein molecules. …
