A membrane is a thin, flexible layer of tissue or material that separates, covers, or connects parts. In biology, cell membranes control what enters and leaves the cell.
From Latin “membrana” meaning 'parchment, skin', related to “membrum” 'limb, part'. It originally referred to thin animal skins used as writing material. Science later borrowed it to describe thin biological layers and artificial films.
The first 'membranes' were literally animal skins stretched for writing—early notebooks. Cell membranes act like intelligent borders: they’re not just walls, but selective gates that constantly decide what can pass.
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