Osmotic potential pressure

Weed Extract in Nutrient Medium (g ml) Abaxial Leaf Resistance (sec/cm) Water Potential (bars) Osmotic Potential (bars) Turgor Pressure (bars)... 

Possible driving forces for solute flux can be enumerated as a linear combination of gradient contributions [Eq. (20)] to solute potential across the membrane barrier (see Part I of this volume). These transbarrier gradients include chemical potential (concentration gradient-driven diffusion), hydrostatic potential (pressure gradient-driven convection), electrical potential (ion gradient-driven cotransport), osmotic potential (osmotic pressure-driven convection), and chemical potential modified by chemical or biochemical reaction. 

Angiotensin II has two effects first, as a vasoconstrictor acting via receptors on vascular smooth muscle cells, and second, it stimulates the adrenal cortex gland to produce aldosterone (a mineralocorticoid steroid hormone, see Chapter 4). Aldosterone promotes the reabsorption of sodium from the renal tubule into the bloodstream and the resulting increase in osmolality (osmotic potential) of the blood causes water reabsorption in the nephrons. The outcome is an increase in blood volume and, therefore, pressure which inhibits (by negative feedback) further renin secretion from the JGA. 

The mechanism of action by which silane and siloxanes reduce expansion has been attributed to water repellence and air entrainment. Phosphate addition or coatings may interfere with the dissolution of silica gel and the formation of gel. It is also possible that phosphate reduces the osmotic potential and the swelling pressure in the gel. The manner in which air entrainment reduced expansion was attributed to the accommodation of alkali-silica gel in the air void system. For example, it was found that air-entrained concrete with 4% air voids could reduce AAR expansion by 40% [23]. 

Figure 2.6 Chemical potential, pressure, and solvent activity profiles through an osmotic membrane following the solution-diffusion model. The pressure in the membrane is uniform and equal to the high-pressure value, so the chemical potential gradient within the membrane is expressed as a concentration gradient...

Calculate the osmotic potential of a water sample with a concentration of 3000 ppm dissolved solids. Convert ppm to (a) mg L 1, (b) mmhos cm-1, and (c) osmotic pressure in bars. Explain whether the salt content of this water would be too high for plants. 

Subsequent tests with velvetleaf, Kodkia, Jerusalem artichoke, and cocklebur showed that their allelopathic action altered water balance (55,94,95). Growth reductions in sorghum and soybean seedlings in nutrient solution amended with extracts from these weeds correlated with high diffusive resistances and low leaf water potentials. Stomatal closure occurred in plants treated with the more concentrated extracts. Depressions in water potential were due to a reduction in both turgor pressure and osmotic potential. A lower relative water content was also found in velvetleaf-treated plants. These impacts on water balance were not from osmotic factors. Allelochemicals from these weeds have not been thoroughly ascertained, but the present evidence shows that some contain phenolic inhibitors. Lodhi (96) reported that Kodkia contains ferulic acid, chlorogenic acid, caffeic acid, myricetin, and quercetin. As noted earlier, an effect on plant-water relationships is one mechanism associated with the action of ferulic acid. 

Unfortunately, the use of the terms osmotic pressure and osmotic potential, as well as their algebraic sign, varies in the literature. Osmotic pressures have been measured using an osmometer (Fig. 2-8), a device having a membrane that ideally is permeable to water but not to the solutes present. When pure water is placed on one side of the membrane and some solution on the other, a net diffusion of water occurs toward the side with the solutes. To counteract this tendency and establish equilibrium, a hydrostatic pressure is necessary on the solution side. This pressure is often called the osmotic... 

Scholander, P.F., Hannnel, H.T., Hemmingsen, E.A., and Bradstreet, E.D. 1964. Hydrostatic pressure and osmotic potential in leaves of mangroves and some other plants. Proc. Natl... 

Related to osmotic pressure is osmotic potential. Osmotic potential is a partial measure of a system s free energy. Pure water is arbitrarily assigned an osmotic potential of zero. When a solute is added, the osmotic potential becomes negative. At constant temperature and pressure, water flows from higher osmotic potential to lower osmotic potential. Water potential, another related term, is similar to osmotic potential but takes into account temperature and pressure. Water potential is essentially the same as free energy. When water and the solution in the diagram below have come to equilibrium, points A and B have the same water potential, but the osmotic potential of point B is less than that of point A. 

To calculate the additional pressure, A P, needed to transfer additional volume, AF, of solvent from the solution through the membrane to the pure solvent side, a system can be considered in which the initial volume of the solution is smaller by AF, or Vs = Vs - AV, and in which the total amount of solute does not change, namely, = ng and W = fV. As already explained, this new state will result in a higher osmotic potential, hence a higher osmotic pressure, n > n. Consequently, the applied pressure needed for keeping the system in a constant state will equal the new osmotic pressure. Thus... 

Free energy change, which consists of matric potential, osmotic potential and gravity potential, is equal to potential swelling pressure (Nakano et al.(1984)). In the case of buffer material, it is approximately equal to the suction, because the... 

Comparison of theory with experiment. It will be shown in Section 13.3.2.1 that the flat plate potentials can be used to calculate the osmotic disjoining pressures in concentrated monodisperse sterically stabilized dispersions. Evans and Napper (1977) have compared the theoretical predictions using the above equations with those measured by Homola and Robertson (1976) for polystyrene latex particles stabilized by poly(oxyethylene) of molecular weight ca 2 000 in aqueous dispersion media. The elastic repulsion in the interpenetrational-plus-compressional domain was estimated from the following expression for the constant segment density model... 

To simplify the analysis, the cell is first allowed to equilibrate its water chemical potential zf/iw = /iw(l)-/ w(0) occurring in Eq. (26) and achieve a turgor pressure above the atmospheric pressure corresponding to its osmotic potential. As the H pump is switched on, the flux of water into the cell will raise its turgor pressure above Pq. This pressure difference P—Po will be written a Ap, and in the above equations (25) and (26) Ap will be replaced by V Ap, where Fvv is the partial molal volume of water. ... 

A mathematical description of steady-state growth is provided by recent restatements of the Lockhart equation [1]. This relates internal and external osmotic potentials, cell wall properties and hydraulic conductance to growth rate. Co-variations of growth rate and turgor pressure at various growth temperatures are detailed for wild-type and slender seedlings in Fig. 1. 

A polymer will absorb solvent until the solvent chemical potentials in the polymer (gel) phase and in the free solution are equal. This statement can be rewritten in terms of osmotic swelling pressure, which is zero at equilibrium [8] ... 

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