The plasma membrane is composed of a phospholipid bilayer, which is two layers of phospholipids back-to-back. Phospholipids are lipids with a phosphate group attached to them. Basic purpose of this lecture is to present on Cell Structure; major focus on Plasma Membrane. Lipid Bilayer and protein Pores are main functions of Plasma Membrane. Nucleus, Ribosomes, Endoplasmic Reticulum are also part of Plasma Membrane. The plasma membrane is the boundary between the cell structure and its environment.