Phospholipid molecules are amphiphilic in nature. That is, the molecule has both a hydrophobic and a hydrophilic end. In general, the hydrophobic end is a fatty acid "tail" (actually there are two such tails) and the hydrophilic phosphate end is considered the 'head'. Given this unique structure, phospholipids are structured to interact with both hydrophobic and hydrophilic molecules. When placed in water, the hydrophilic ends get submerged, while the hydrophobic tails point outwards. The amphiphilic nature of the phospholipids is important for the plasma membrane which is a lipid bilayer. The membrane consists of two layers of these phospholipid molecules, with hydrophilic ends pointing outwards and hydrophobic ends pointing inwards towards each other. This unique lipid bilayer structure allows selective permeability to the plasma membrane, allowing cell access to some molecules, while restricting it for others.
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