Final answer:
Cholesterol (d) is the membrane lipid that does not contain a fatty acid tail. It differs from phospholipids which have both a glycerol backbone and fatty acid chains.
Step-by-step explanation:
The membrane lipid that does not contain a fatty acid tail is cholesterol (d). Unlike phospholipids, which have a glycerol backbone with two fatty acid chains and a phosphate group, cholesterol is composed of a ring structure and does not have the fatty acid tail that is characteristic of other lipid molecules such as phosphatidylcholine or phosphatidylserine.
Phospholipids are crucial components of the plasma membrane of cells, and they help maintain membrane fluidity. Phospholipids orient their hydrophobic tails towards each other and their hydrophilic heads towards the exterior and interior aqueous environments, forming a lipid bilayer. Cholesterol is also found within the cell membrane, where it is strategically positioned to modulate fluidity and structural integrity.