Which statement best describes the structure of a phospholipid?

The correct choice highlights the characteristic structure of phospholipids, which are essential components of cell membranes. A phospholipid consists of a hydrophilic (water-attracting) head and two hydrophobic (water-repelling) tails. The hydrophilic head is typically composed of a phosphate group and additional functional groups that attract water, while the hydrophobic tails are made of long fatty acid chains that do not interact favorably with water.

This unique arrangement allows phospholipids to form bilayers when in an aqueous environment, with the hydrophilic heads facing outward towards the water and the hydrophobic tails tucked away from the water in the interior. This bilayer structure is fundamental to the formation of cell membranes, providing a barrier that separates the cell from its external environment while allowing selective permeability.

In contrast, the other choices do not accurately represent the structure of phospholipids. They either misstate the number of heads and tails or incorrectly categorize their hydrophilic and hydrophobic properties, failing to capture the essential characteristics needed for phospholipid functionality.