Diffusion Across a Selectively Permeable Membrane

The vital activity of any living organism is determined by the vital activity of its constituent units-cells. The main structure of any cell that regulates it is the biological membrane. Possessing selective permeability, the biological membrane regulates the concentration of metabolic products, their transport and metabolism in the cells and their parts itself. The regulation of the metabolism through membranes depends, on the one hand, on the activity of the cell itself, and on the other hand, on the chemical properties of the membranes. To start from the beginning, let’s clary some questions: what name is given to the process by which water crosses a selectively permeable definition? what is the definition of membrane being selectively permeable? and how does diffusion help in transferring the material inside the cell? Definition of Diffusion Diffusion is the process of a substance spreading out from its origin. Molecules diffuse through random molecular motion which allows some substances to pass more easily than others. In science, they can be called selectively permeable membranes. The term permeability is explained as the ability of cells and tissues to absorb, secrete and transport chemicals, passing them through cell membranes, vessel walls and epithelial cells. Cells are selectively permeable, meaning that their membranes allow some substances to cross easily while others are unable to cross without assistance. Cell membranes are selectively permeable, in part because its pores are small, allowing the cell to prevent larger molecules from moving across the membrane. Living cells are always in a state of continuous exchange of chemicals with each other and the environment itself. This process of moving, interchanging and permeability is always happening, even when a system appears to have reached equilibrium, because molecules are always moving. Selectively permeable membrane However, there are some obstacles in substances being transferred through. Sometimes diffusing particles encounter regions in which the permeability is reduced, but not zero. One example of such a region is called a membrane, a thin barrier that might be made of cellulose, plastic, glass, or phospholipid; or the barrier might be a biological membrane consisting of a complex mixture of lipids and proteins. In addition, membranes alter the rate at which particles can diffuse, and they do so selectively. That is, they allow some particles to pass freely, retard the passage of others to varying degrees and completely prevent the passage of still others. Indeed, cells use a whole array of membrane proteins, called carriers and channels, to regulate (and sometimes rapidly change) the permeability of what would otherwise be an impermeable lipid bilayer. Membranes, through their selective alteration of the otherwise inexorable process of diffusion, cause a number of interesting cellular phenomena. When water can cross the membrane and dissolved particles cannot, osmosis occurs. When charged particles can cross and those with the opposite charge can not, diffusion potentials are generated. In other words, if the speed of the solutes molecule transferred through the molecule’s membrane is commensurable with the speed of the water molecules being transferred, the magnitude of such forces will be close to zero. Thus, no osmotic change in cell volume. But if the cell membrane is impenetrable for a given substance, then the osmotic change in cell volume is goes to its maximum. Of course, the speed or the rate of molecular penetration through the cell membrane depends on the size of the molecule. To conclude, living cells, like the organism as a whole, are an open system with a constant exchange of material and energy. During this exchange, the process of permeability of the substances takes place in the cell through membranes. The study of the structures and characteristics of biological membranes plays an important role in medicine, since many pathological processes in the cell are associated with a violation of membrane functions. Violation of the functions of cellular and intracellular membranes underlies irreversible cell damage and, as a consequence, the development of severe diseases of the cardiovascular, nervous, endocrine system which have enormous effect on humans health.