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 discussed 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 Latin, 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 separate segments using similar internal structures. This structure provides the spatial distribution of various elements and chemical processes.
Structure and function of cell membranes
The existing model of the structure of biological membranes is called fluid-mosaic. It is based on a doublea layer of lipids, the hydrophilic parts of which are turned outward. These are the 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 located outside, others penetrate the double layer of lipids to different depths. This structure allows the cell to carry out complex processes of protection, diffusion, phago- and pinocytosis.
Supramembrane 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 the glycocalyx. It provides a direct connection of the cell with the environment, regulating the selective intake of substances. The functions of the cell wall are due to 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 most dense. This property is ensured by the presence of bundled insoluble cellulose fibers. It is this complex carbohydrate that gives plant cell walls stiffness and strength. We can say that it forms a kind of framework. The composition and function of the cell wall in different tissue types can largelyvary. For example, over time, the cells of one of the varieties of integumentary tissue, which is called a cork, are impregnated with a fat-containing substance, suberin. The result of this is the death of the internal content and the provision of a support function. A similar process is also observed in the cells of the conducting tissue of plants, namely, in the vessels. They become hollow structures, as a result of which the passage of substances becomes possible. The process of lignification occurs due to the fact that the gaps between the cellulose fibers are filled with another complex carbohydrate - lignin. It significantly increases the strength of the surface apparatus.
In fungi, the basis of the cell wall is also made up of polysaccharides. However, it is not cellulose that is predominant, but chitin and glycogen. This is a structural feature that makes them related to animals. But the function of the bacterial cell wall is provided by a complex combination of carbohydrates and proteins. It is called peptidoglycan or murein. This substance is characteristic only for the 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 permanent shape. It protects all internal contents from mechanical influences of the environment. The functions of the cell wall are also in the implementation of a continuous processwater entering the cell with nutrients dissolved in it and vice versa.
Cell wall permeability
The process of metabolism carried out by the cell wall 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 exfoliation of a layer of cytoplasm located directly near the cell wall. This requires certain conditions. Plasmolysis occurs, for example, if a cell is placed with a higher s alt concentration than in its own cytoplasm. The reverse process is called deplasmolysis.
Thanks to the pores that are in the cell walls, there is also an exchange of substances between cells. This is directly carried out with the help of plasmodesmata. These formations are the way of transporting 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 the substances necessary for the development of organisms take 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.
