In a phospholipid bilayer, which part is hydrophobic?

In a phospholipid bilayer, the hydrophobic part consists of the water-hating tails. Phospholipids are composed of two distinct regions: the hydrophilic (water-loving) heads and the hydrophobic (water-hating) tails. The hydrophobic tails, which are made of long fatty acid chains, tend to avoid water and are oriented inward toward each other, forming the core of the bilayer. This arrangement is fundamental to the structure and function of cell membranes, as it creates a barrier that protects the cell's internal environment from the aqueous surroundings.

The hydrophilic heads, on the other hand, face outward towards the water inside and outside of the cell, facilitating interactions with the surrounding aqueous environment. Protein channels are embedded within the bilayer and often interact with both hydrophilic and hydrophobic components, serving various functions but not constituting the hydrophobic part of the bilayer itself. The membrane as a whole encompasses both the hydrophobic tails and the hydrophilic heads, but it is specifically the tails that exhibit hydrophobic properties.