The part of the phospholipid that is hydrophilic is known as:

In this context, the hydrophilic portion of a phospholipid is represented by the polar head. Phospholipids are essential components of cell membranes, and they consist of two main parts: the hydrophilic (water-attracting) polar head and the hydrophobic (water-repelling) fatty acid tails.

The polar head is typically composed of a phosphate group and may be linked to an additional group such as choline, serine, or ethanolamine, which all contribute to its water-loving nature. This hydrophilic character allows the polar head to interact favorably with the aqueous environment both inside and outside the cell.

This arrangement is critical for the formation of the lipid bilayer that makes up cell membranes, where the hydrophobic tails face inward, shielded from water, while the hydrophilic heads face outward towards the water, maintaining the structure and function of the membrane. Understanding the distinct properties and roles of these components helps to elucidate how phospholipids contribute to cellular function and membrane integrity.