Modern technology makes it possible to study the component of cell. “The outer most covering or boundary of the cell the enclosed the component of cytoplasm is called plasma membrane”. Cell membrane is chemically made up of lipid and protein. About 60-80% protein and rest of 20-40% lipid. Moreover, carbohydrates are also present in small quantity. Many biologist contributed to establish the structural organization of cell membrane.
There are many concept given by biologist regard to plasma membrane. Two of the most important models are given below.
MODEL NO.1 (UNIT MEMBRANE):
It was proposed earlier that cell membrane is chemically make up of bilayer of lipid that are sandwiched between the outer and inner layer of protein. This structure is given by the name of unit membrane. And found in cellular organelles. But modern research did not support it that lipid are not sandwiched into the protein layer.
MODEL NO. 2 (FLUID MOSAIC MODEL):
This model is most acceptable is based modern research and most acceptable. The layer of protein is not continuous . protein layer is embedded in lipid layer in a mosaic manner. This discovery led to FLUID MOSAIC MODEL. Cell membrane also have charged pores through which allow material movement by active and passive transport.
Transport offers a barrier between cytoplasm component and environment around the cell. Only specific material can pass through it .. this is called selectively permeable membrane. The lipid soluble substance can easily pass through the pores but ions have some difficulty in crossing. In animal cell cell membrane take food with the help of endocytosis process.