Final answer:
The element is not part of the plasma membrane, which consists of a phospholipid bilayer, proteins, and cholesterol that provides flexibility and is found within the tail bilayer.
Step-by-step explanation:
The component that isn't part of the plasma membrane is element. The plasma membrane is composed of a phospholipid bilayer, proteins, and cholesterol which provide flexibility to the membrane. Phospholipids form the main structure of the membrane, proteins such as ion channels and receptor proteins play various roles including transport and cell-signaling, and carbohydrates aid in cellular recognition. Cholesterol is specifically located within the tail bilayer region, where it helps to maintain the integrity and fluidity of the membrane.