The most theory adopted in the modern biology is that living organisms comprises of two basic categories cell, that is prokaryotic cell or single cell, such as bacteria, and eukaryotic cell or multi-cellular, which have more complex interior. As the more complex cell, eukaryotic has various structures (organelles) in the cell. One of the most fundamental structures is the plasma membrane. In regard to the crucial roles of the plasma membrane, which is a part of the cell as the basic unit of life, will there be a life on earth if there is no cell membrane? The following components are going to be discussed in more detail; firstly, interconnecting between the structure and the function of the cell membrane, next the roles of the cell membrane plasma in cells, finally the relation between cell membrane surrounding the cell and other membrane in the cell.
All membranes in the eukaryotes cell consist of a double layer (bilayer) of phospholipids where attached several proteins and cholesterol. In addition the phospholipids have both polar hydrophilic head and a pair of non-polar hydrophobic tails, hence the hydrogen bonds can form between water and the phospholipids head. The hydrophobic interactions cause the phospholipids to hide inside the bilayer. Since the individual phospholipids molecules are not bound to one another, consequently this bilayer is fairly fluid and individual molecule can move around freely yet it depends upon the surrounding temperature i.e. temperature. Nevertheless they can easily move around, the hydrophobic tails are still mutually attached which can acts as a barrier for those polar substances, for example, amino acids, sugar and salts. Many protein and cholesterol embedded in plasma membrane particularly to the part that stick outside the cell also have carbohydrate group attached to them, this cholesterol is called glycolipid, which serve as recognition signals for interactions between cells, and the protein called glycoprotein, which is enable cell to recognise foreign substance.