Final answer:
The phosphate group and its linked hydrophilic group form the phospholipid head, which is part of a phospholipid molecule exhibiting both hydrophilic and hydrophobic characteristics, known as being amphipathic.
Step-by-step explanation:
The small hydrophilic group linked to phosphate and the negatively charged phosphate itself form a highly water-soluble domain called the phospholipid head. Phospholipid molecules are amphipathic, meaning they have both a hydrophilic (water-loving) region and a hydrophobic (water-fearing) region. The phospholipid has a glycerol backbone attached to two fatty acid tails that are hydrophobic, and a phosphate group that is hydrophilic, often bound to a small organic group such as choline, serine, ethanolamine, or inositol. When part of a cell membrane, the phosphate heads face the extracellular and intracellular watery environments, while the fatty acid tails face each other, creating a bilayer that is fundamental to the structure and function of the membrane.