Final answer:
Phosphatidylserine is the specific phospholipid that is found in the plasma membrane's inner layer in living cells.
Step-by-step explanation:
The phospholipid found in the plasma membrane that occurs only in the inner layer of the lipid bilayer in normal living cells is called phosphatidylserine. Phospholipids are composed of fatty acid chains attached to a glycerol or sphingosine backbone, but instead of three fatty acids as in triglycerides, there are two fatty acids forming diacylglycerol, and the third carbon of the glycerol backbone is occupied by a modified phosphate group. Phosphatidylserine is an important membrane phospholipid that plays key roles in cell signaling and membrane structure.