Final answer:
The major type of lipid found in cell membranes is phospholipids, which are composed of two fatty acids, a glycerol backbone, and a modified phosphate group.
Step-by-step explanation:
The major type of lipid found in cell membranes is phospholipids. These molecules are essential constituents of the plasma membrane, composed of two fatty acid chains and a glycerol or sphingosine backbone.
Unlike triglycerides, which have three fatty acid chains, phospholipids contain a modified phosphate group instead of the third fatty acid.
This structure forms a hydrophilic head and a hydrophobic tail, allowing for the formation of the bilayer that is characteristic of cell membranes, creating a barrier that protects the cell while still providing fluidity and permeability necessary for the function of living cells.