In: Biology
a) Cell membrane is the structure which enclose most of the organelles and also the entire cell. It acts as a barrier for the entry of unwanted substances into the cell. It allows transport of essential nutrients in to the cell and movement of waste products outside the cell.
b) Cell membranes are complex in composition. They are composed primarily of fatty acid based lipids such as phospholipids and sterols (mainly cholesterol) and proteins. Membrane composition is not set and changes according to its environment and different stages of cell development.
c) The cell membranes are composed of variety of biological molecules notably lipids and proteins. Mainly two types of lipids are found in the membranes: phospholipids and sterols (cholesterol). Membrane proteins are of two types depending upon their location in the membrane: extrinsic and intrinsic proteins. Extrinsic proteins are loosely attached by ionic bonds or calcium bridges to the electrically charged phosphoryl group of the bilayer. On the other hand intrinsic proteins are embedded within the phospholipid bilayer. The membrane lipids have defining characteristics of lipid- they dissolve readily in organic solvents and in addition have a region attracted to and soluble in water. These lipids arrange themselves in such a way that the hydrophobic tails of phospholipids are faced towards each other of the bilayer and the hydrophilic head portion is faced towards the outside of the bilayer where it can interact with hydrophilic environment.