Big Chemical Encyclopedia

Chemical substances, components, reactions, process design ...

Articles Figures Tables About

Plasma membrane semipermeable

Pfeffer in 1877 [523] subjected plant cell suspensions to different amounts of salt and observed the cells to shrink under hypertonic conditions and swell in hypotonic conditions. He concluded there was a semipermeable membrane separating the cell interior from the external solution, an invisible (under light microscope) plasma membrane. [Pg.119]

The plasma membrane is semipermeable because it is not permeable to all solute particles present. As a result, it maintains a concentration difference for many ions and molecules across itself, although water crosses the membrane freely in either direction. The movement of water in and out of the... [Pg.12]

Most of the early work on membranes was based on experiments with erythrocytes. These cells were first described by Swammerdam in 1658 with a more detailed account being given by van Leeuwenhoek (1673). The existence of a cell (plasma) membrane with properties distinct from those of protoplasm followed from the work of Hamburger (1898) who showed that when placed in an isotonic solution of sodium chloride, erythrocytes behaved as osmometers with a semipermeable membrane. Hemolysis became a convenient indication of the penetration of solutes and water into the cell. From 1900 until the early 1960s studies on cell membranes fell into two main categories increasingly sophisticated kinetic analyses of solute translocation, and rather less satisfactory examinations of membrane composition and organization. [Pg.158]

Osmosis, water movement across a semipermeable membrane driven by differences in osmotic pressure, is an important factor in the life of most cells. Plasma membranes are more permeable to water than to most other small molecules, ions, and macromolecules. This permeability is due partly to simple diffusion of water through the lipid bilayer and partly to protein channels (aquaporins see Fig. 11-XX) in the membrane that selectively permit the passage of water. Solutions of equal osmolarity are said to be isotonic. Surrounded by an isotonic solution, a cell neither gains nor loses water (Fig. 2-13). In a hypertonic solution, one with higher... [Pg.57]

The physical properties of aqueous solutions are strongly influenced by the concentrations of solutes. When two aqueous compartments are separated by a semipermeable membrane (such as the plasma membrane separating a cell from its surroundings), water moves across that membrane to equalize the osmolarity in the two compartments. This tendency for water to move across a semipermeable membrane is the osmotic pressure. [Pg.58]

The plasma membrane is a delicate, semipermeable, sheetlike covering for the entire cell. Forming an enclosure prevents gross loss of the intracellular contents the semipermeable character of the membrane permits the selective absorption of nutrients and the selective removal of metabolic waste products. In many plant and bacterial (but not animal) cells, a cell wall encompasses the plasma membrane. The cell wall is a more porous structure than the plasma membrane, but it is mechanically stronger because it is constructed of a covalently cross-linked, three-dimensional network. The cell wall maintains a cell s three-dimensional form when it is under stress. [Pg.8]

Did you observe any difference in the behavior of plant cells versus red blood cells in hypotonic and hypertonic solutions What were those differences Red blood cells have only semipermeable plasma membranes, while plant cells have an additional cell wall made of polysaccharides. Would that explain your observations How ... [Pg.202]

Water tends to move across a semipermeable membrane from a solution of low solute concentration to one of high concentration, a process termed osmosis, or osmotic flow. In other words, since solutions with a high concentration of dissolved solute have a lower concentration of water, water will spontaneously move from a solution of high water concentration to one of lower. In effect, osmosis Is equivalent to diffusion of water. Osmotic pressure is defined as the hydrostatic pressure required to stop the net flow of water across a membrane separating solutions of different compositions (Figure 7-24). In this context, the membrane may be a layer of cells or a plasma membrane that Is permeable to water but not to the solutes. The osmotic pressure Is directly proportional to the difference in the concentration of the total number of solute molecules on each side of the membrane. For example, a 0.5 M NaCl solution is actually 0.5 M Na ions and 0.5 M Cl ions and has the same osmotic pressure as a 1 M solution of glucose or sucrose. [Pg.271]

In multicellular organisms, thin lipid membranes serve as semipermeable barriers between aqueous compartments (Figure 5.1). The plasma membrane of the cell separates the cytoplasm from the extracellular space endothelial cell membranes separate the blood within the vascular space from the rest of the tissue. Properties of the lipid membrane are critically important in regulating the movement of molecules between these aqueous spaces. While certain barrier properties of membranes can be attributed to the lipid components, accessory molecules within the cell membrane—particularly transport proteins and ion channels—control the rate of permeation of many solutes. Transport proteins permit the cell to regulate the composition of its intracellular environment in response to extracellular conditions. [Pg.113]

The plasma membranes of cells are semipermeable in other words they are permeable to water and a select group of small molecules, but are impermeable to large molecules and many ions. If the total concentrations of solutes on either side of a semipermeable membrane are different, water diffuses from the region of low solute concentration to the region of high solute concentration imtil the solute concentrations are the same on both sides. This process is called osmosis, and the difference in water pressiue across the cell membrane is called the osmotic pressure. [Pg.55]

The plasma membrane is a semipermeable lipid bilayer between the cell wall and the inside of the cell. There are several distinct roles that the plasma membrane carries out such as to provide a barrier to free diffusion of solutes, to catalyse specific exchange reactions, to store energy dissipation, to provide sites for binding specific molecules involved in metabolic signalling pathways and to provide an organized support matrix for the site of enzyme pathways involved in the biosynthesis of other cell components (Hazel Williams, 1990). The plasma membrane is quite fluid and... [Pg.7]

A great deal of attention has been directed to the anaerobic fermentation by yeasts, notably Saccharomyces cerevisiae in its various forms (top and bottom brewers and bakers yeast). This has been industrially important, and the subspherical cells, about 6-8 /n in diameter, are produced under standard conditions. They can be brought into suspension with little or no clumping. They are then suitable for tests of the permeation through the surface of the suspended cells. From the discussion on pages 9-13, it follows that permeation can be treated either as the diffusion into spheres, where there is no semipermeable plasma membrane, or as the unidimensional diffusion through a relatively thin, slightly permeable membrane, with substantial complete diffusion of permeant. Since there is every reason to assume the latter case, the former case is considered unimportant. [Pg.13]

Introduction of a water-soluble ionic substance into the vascular system results in an increase in the number of particles in the bloodstream as the contrast substance dissolves. The body possesses several internal regulation systems and, when perturbed by an injection, attempts to restore the concentrations of substances in the blood to their normal or preinjection levels. To re-equilibrate the system, water from the cells of surrounding body tissue moves into the blood plasma through capillary membranes. This transfer of water is an example of osmosis, the diffusion of a solvent (water) through a semipermeable membrane (the blood vessels) into a more concentrated solution (the blood) to equalize the concentrations on both sides of the membrane. To accommodate the increase in... [Pg.128]

The pressure that would be required to prevent the movement of water across a semipermeable membrane owing to the osmotic effect of large plasma proteins. (nc mmHg). [Pg.159]

By far, the most advanced technology in cnrrent nse is the hollow fiber techniqne. It has been reviewed extensively in the literature. Briefly, this configuration involves the cultivation of hepatocytes on the external surfaces of semipeimeable capillary hollow fiber membranes bundled together within a plastic shell. Nutrients and ultimately plasma from patient blood are circulated through the fibers. The cells in the capillaries provide hepatic function. In the current versions of this technology, cultured porcine hepatocytes are protected from the body s immune system by the semipermeable capillary membrane. [Pg.155]

The total concentration of dissolved particles inside red blood cells is approximately 0.30 M, and the membrane surrounding the cells is semipermeable. What would the osmotic pressure (in atmospheres) inside the cells become if the cells were removed from blood plasma and placed in pure water at 298 K ... [Pg.455]

The following processes can be described as selective therapeutic plasmapheresis. In a first step, blood is withdrawn from the patient and separated by crossflow filtration in a hollow-fiber membrane cartridge water and some plasma solutes are transferred through a semipermeable membrane under a convection process. The transmembrane pressure applied from blood to filtrate compartment ensures flow and mass transfers. Then, the filtrate perfuses the adsorption columns where toxins are retained and is finally mixed with blood cells and other plasma components before returning to the patient (Figure 18.11). [Pg.428]

The peritoneum has a surface area of about 2 m. It has the effect of a semipermeable membrane and can transport a total of 720-840 ml/day between the plasma and the peritoneal cavity. Spontaneous diuresis allows 300 mllday to be excreted, whereas with the use of diuretics some 500 mllday are possible. The presence of peripheral oedema, however, permits a loss of fluid of about 900 mllday (L. Shear et al., 1970). [Pg.306]


See other pages where Plasma membrane semipermeable is mentioned: [Pg.8]    [Pg.12]    [Pg.175]    [Pg.372]    [Pg.379]    [Pg.368]    [Pg.269]    [Pg.745]    [Pg.379]    [Pg.164]    [Pg.234]    [Pg.168]    [Pg.5801]    [Pg.145]    [Pg.514]    [Pg.17]    [Pg.374]    [Pg.154]    [Pg.269]    [Pg.116]    [Pg.462]    [Pg.125]    [Pg.406]    [Pg.201]    [Pg.368]    [Pg.274]    [Pg.116]    [Pg.700]    [Pg.701]   
See also in sourсe #XX -- [ Pg.12 ]




SEARCH



Membranes plasma

Semipermeability

Semipermeable

Semipermeable membrane

© 2024 chempedia.info