Semipermeable Allowing passage molecules

Osmosis is the movement of solvent molecules through a semipermeable membrane. The membrane is a thin, pliable sheet of material, perforated with molecular-scale holes. The holes are large enough to allow water molecules to pass back and forth through the membrane, but too small to allow the passage of solute molecules or hydrated ions hence, the membrane is semipermeable. 

Certain materials, including those that make up the membranes around living cells, are semipermeable. That is, they allow water or other small molecules to pass through, but they block the passage of large solute molecules or ions. When a solution and a pure solvent (or two solutions of different concentration) are separated by the right kind of semipermeable membrane, solvent molecules pass... 

A semipermeable membrane allows only certain types of molecules to pass through. Typical membranes allow passage of water and small molecules, but not large molecules or ions. 

Imagine a semipermeable membrane that prevents passage of A molecules, but allows passage of B molecules. The difference of pressure across this membrane is called the osmotic pressure of A molecules (see Section 1.7.1). The osmotic pressure is defined as the rate of change of the total free energy of the system ATmix = nAFmix with respect to volume at constant number of A molecules ... 

Reverse osmosis employs a semipermeable membrane that allows passage of the solvent molecules, but not those of the dissolved organic and inorganic material. A pressure gradient is applied to cause separation of the solvent and solute. Any components that may damage or restrict the function of the membrane must be removed before the process is performed. Capital investment and operating costs depend on the waste stream composition. 

An extremely thin piece of material such as a sheet of synthetic polymer or animal tissue can allow some molecules to pass through it. Such a material is called a membrane and is said to be permeable to those molecules and ions that can pass through. Permeability is dependent on the presence of tiny passages within the membrane. A membrane permeable to water molecules but not to ions or molecules larger than water molecules is called a semipermeable membrane. Many membranes made from synthetic polymers have this characteristic. One such polymer is cellulose acetate. If a semipermeable membrane is placed between seawater (brine) and pure water, the pure water will pass through the membrane to dilute the seawater. This is a process called osmosis. The hquid level on the seawater side rises as more water molecules enter than leave, and pressure is exerted on the membrane until the rates of diffusion of water molecules in both directions are equal. Osmotic pressure is defined as the external pressure required to prevent osmosis. Figure 11.10a and 11.1 Ob illustrates the concepts of osmosis and osmotic pressure. 

NeuraWrap Integra Life Sciences Type I collagen Semipermeable inner membrane allows passage of small molecules but prevents escape of growth factor outer membrane prevents scar ingrowth... 

The phenomenon of osmosis is the passage of a pure solvent into a solution separated from it by a semipermeable membrane, a membrane that is permeable to the solvent but not to the solute (Fig. 3.34). The membrane might have microscopic holes that are large enough to allow water molecules to pass through, but not ions or carbohydrate molecules with their bulky coating of hydrating water molecules. The osmotic pressure, 17 (uppercase pi), is the pressure that must be applied to the solution to stop the inward flow of solvent. 

The Colloid-Osmotic Pressure. Besides semipermeable membranes which allow passage only for water and not for dissolved substances, there are also those which allow substances of low molecular weight, but not of high molecular weight, to penetrate. It can easily be seen that there may be pores whose diameter is smaller than that of protein molecules. In this case, salts can diffuse freely and give no cause for differences in pressure, while the law of osmosis still applies to macromolecules. Since the number of macromolecules is relatively small, the pressures that result from them commonly are small, too. The organism, however, can develop mechanical... 

If you were to place a solution and a pure solvent in the same container but separate them by a semipermeable membrane (which allows the passage of some molecules, but not all particles) you would observe that the level of the solvent side would decrease while the solution side would increase. This indicates that the solvent molecules are passing through the semipermeable membrane, a process called osmosis. Eventually the system would reach equilibrium, and the difference in levels would remain constant. The difference in the two levels is related to the osmotic pressure. In fact, one could exert a pressure on the solution side exceeding the osmotic pressure, and solvent molecules could be forced back through the semipermeable membrane into the solvent side. This process is called reverse osmosis and is the basis of the desalination of seawater for drinking purposes. These processes are shown in Figure 13.1. 

Semipermeable Membrane media that allows the passage of solvent molecules but blocks solute molecules Shortwave Radiation radiation emitted by the Sun that passes through and interacts with the atmosphere... 

Water molecules tend to move from a region of higher water concentration to one of lower water concentration. When two different aqueous solutions are separated by a semipermeable membrane (one that allows the passage of water but not solute molecules), water molecules diffusing from the region of higher water concentration to that of lower water concentration produce osmotic pressure (Fig. 2-12). This pressure, n, measured as the force necessary to resist water movement (Fig. 2-12c), is approximated by the van t Hoff equation ... 

How does a semipermeable membrane allow for the passage of water molecules but not any solute ions or molecules ... 

OSMOTIC PRESSURE. Pressure that develops when a pure solvent is separated from a solution by a semipermeable membrane which allows only the solvent molecules to pass through it. The osmotic pressure of the solution is then the excess pressure which must be applied to the solution so as to prevent the passage into it of the solvent through the semipermeable membrane. 

Osmosis is the selective passage of particular components of a solution through a semipermeable membrane. Usually, it is the solvent that passes through the membrane, because the solute is blocked. However, some membranes also allow small solute molecules to pass through as well and only block the passage of macromolecular solute molecules. The osmotic pressure of a solution is the pressure difference produced at equilibrium across the membrane, with the solution on one side of the membrane and pure solvent on the other side. As shown in Fig. 4, the reduced activity of the solvent in solution is compensated for by an increase in the pressure of the solution ... 

The membrane selectivity toward an osmotic agent and water, described by the osmotic reflection coefficient a. An ideal semipermeable membrane has the a value of 1, which means that it allows the passage of only water molecules. In contrast, a leaky semipermeable membrane with a value approaching zero does not exhibit such selectivity and permits the transport of not only water, but also an osmotic agent. 

Reverse osmosis. By applying enough pressure on the solution side, fresh water can be made to flow from right to left. The semipermeable membrane allows the passage of water molecules but not of dissolved ions. 

Consider a reaction that occurs in a vessel containing a semipermeable membrane that allows only one of the components to pass through it (for example, a small molecule such as hydrogen) but will not allow the passage of large molecules. With such a membrane, the chemical potential of the permeable component can be kept constant in the reaction vessel. 

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