The surface apparatus is an integral part of any cell and many of its components. It performs vital functions. How the cell membrane works , the structure and functions of this structure - everything will be considered in our article.
Cell membrane system
Everyone knows that the cell is the smallest structural and functional unit of the body, and its main parts are the surface apparatus, cytoplasm and organelles. However, its structure can be considered in another way. Any cell is a system of biological membranes. Translated from the Latin language, this term means “film” or “peel”. So, on top of the cells are covered with a plasma membrane. But the internal environment of the cell is divided into individual segments using similar internal structures. Such a structure provides the spatial distribution of various elements and chemical processes.
The structure and functions of cell membranes
The existing model of the structure of biological membranes is called liquid mosaic. It is based on a double layer of lipids, the hydrophilic parts of which are facing outward. These are phosphate groups of these substances. But the hydrophobic parts of lipids, which are compounds of fatty acids, are turned inside the bilayer. The next component of cell membranes are proteins. Some of them are superficial and are located outside, while others penetrate the double layer of lipids to different depths. This structure allows the cell to carry out complex processes of protection, diffusion, phage and pinocytosis.
Supmembrane Cell Complexes
Above the plasma membrane are complexes that perform additional functions. In the cells of plants, fungi and bacteria, they are represented by a cell wall. But in animals, a similar structure is glycocalyx. It provides a direct connection of the cell with the environment, regulating the selective flow of substances. The functions of the cell wall are determined by its structural features, which are somewhat different from the similar structure of animal cells.
Cell wall composition
The chemical structure of the cell wall in different groups of organisms is somewhat different. In plants, it is the densest. This property is ensured by the presence of insoluble cellulose fibers collected in bundles. It is this complex carbohydrate that gives the cell walls of plants rigidity and strength. We can say that it forms a kind of frame. The composition and functions of the cell wall in different types of tissues can vary significantly. For example, over time, the cells of one of the varieties of integumentary tissue called cork are impregnated with a fat-containing substance suberin. The result is the death of the internal contents and the provision of support functions. A similar process is observed in the cells of the conductive tissue of plants, namely in the vessels. They become hollow structures, as a result of which it is possible to conduct substances. The process of lignification occurs due to the fact that the gap between the cellulose fibers is filled with another complex carbohydrate - lignin. It significantly increases the strength of the surface apparatus.
In fungi, polysaccharides also form the basis of the cell wall. However, predominant is not cellulose, but chitin and glycogen. This is a feature of the structure that makes them similar to animals. But the functions of the bacterial cell wall are provided by a complex combination of carbohydrates and proteins. It is called peptidoglycan or murein. This substance is characteristic only of cells of prokaryotic organisms and performs mechanical functions.
Cell wall functions
Despite significant differences in chemical composition, the cell walls of different groups of organisms have a similar specialization. Their main functions are to provide support, protection and metabolism. The cell wall maintains a constant shape. It protects all internal contents from mechanical environmental influences. The functions of the cell wall also consist in the implementation of a continuous process of water entering the cell with the nutrients dissolved in it and in the opposite direction.
Cell wall permeability
The metabolic process that the cell wall carries out is possible due to its permeability. This property is manifested in the implementation of two reverse processes. The first is called plasmolysis. It consists in the detachment of a layer of the cytoplasm located directly near the cell wall. This requires certain conditions. Plasmolysis occurs, for example, if you place a cell with a higher salt concentration than in its own cytoplasm. The reverse process is called deplasmolysis.
Thanks to the pores that are in the cell walls, metabolism between cells also occurs. This is carried out directly using plasmodesm. These formations are the transport of substances. They pass through the plasma membrane and are hollow tubes connecting the EPS of neighboring cells. It is in these organelles that the synthesis and accumulation of all substances necessary for the development of organisms takes place.
So, the cell membrane, the structure and functions of which we examined in our article, is characteristic of all organisms. In plant and bacterial organisms, as well as fungi, a cell wall is located above it. It is formed by polysaccharides, which give it strength. The main functions of the cell wall are protection, support and transport of substances.