The fundamental structure of cell membranes, consisting of two layers of phospholipid molecules arranged with their hydrophilic heads facing outward and hydrophobic tails facing inward. This creates a selective barrier around cells.
From 'phospholipid' (phosphorus-containing lipid) and 'bilayer' (two layers). The concept emerged in the 1920s-1930s as scientists discovered that cell membranes consist of lipid molecules arranged in a double layer formation.
The phospholipid bilayer is like a molecular sandwich that's afraid of water on the inside! The 'water-loving' heads face the watery environments inside and outside the cell, while the 'water-fearing' tails hide in the middle, creating a perfect barrier that's flexible yet selective.
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