Final answer:
The tail end of a phospholipid is hydrophobic and avoids water, while the head portion is hydrophilic and attracts water. Phospholipids in cell membranes form a bilayer with hydrophobic tails facing inward and hydrophilic heads facing outward.
Step-by-step explanation:
The tail end of a phospholipid is hydrophobic, meaning that it does not dissolve in water and tends to avoid water. This hydrophobic characteristic is due to the tail consisting of two fatty acid chains that are largely hydrocarbon in nature. On the other hand, the head portion of a phospholipid is hydrophilic, meaning that it is attracted to water and tends to interact with it. This polar head group contains a phosphate group attached to a glycerol molecule, which allows it to form hydrogen bonds with water molecules.
In a biological membrane, phospholipids are arranged in a bilayer where the hydrophobic tails face inward, shielded from water, and the hydrophilic heads face outward towards the aqueous environment on both sides of the membrane. This arrangement is crucial as it forms the fundamental structure of cell membranes, allowing for the formation of a selective barrier that controls the passage of substances in and out of the cell.