The base of a phospholipid bilayer cake is phospholipids, since they make most of the fluid mosaic model. Phospholipids are made up of two different parts, one hydrophobic and one hydrophilic. Which two elements located in the head of the phospholipids make it polar?

The phosphate groups in the hydrophilic head make it a polar region.

Since it is hydrophilic, it is water-soluble, and is attracted to the liquid.

The fluid mosaic model represents how phospholipids form a double layer as, while the hydrophilic heads join with water and other liquids in the cell, the hydrophobic tails are attracted to each other, forming a bilayer.