Water potential gradient

Cell enlargement occurs when a demand for water is created by relaxation of the cell walls under the influence of turgor pressure and wall-loosening factors. Water enters the cell down a water potential gradient, extending the cell walls (Lockhart, 1965 Boyer, 1985 Tomos, 1985). 

As water moves through the soil pores in response to water potential gradients, it moves with it the solutes dissolved in soil solution. In a rhizosphere context, water moves radially toward the root to replace water taken up by the roots for transpiration. The flux of solute due to water movement (7 .) is simply the product of the rate of water flow at that point and the concentration in soil solution ... 

The equations above describe how solutes in the soil will move in response to concentration or water potential gradients. Such gradients form when the rhizo-sphere is perturbed by the activities of the root including water and MN abstraction and carbon deposition. These activities need to be mathematically described and form one of the two boundary conditions required to solve the initial-value problem. 

Liquid ammonia, which boils at 240 K, is an ionising solvent. Salts are less ionised in liquid ammonia than they are in water but, owing to the lower viscosity, the movement of ions through liquid ammonia is much more rapid for a given potential gradient. The ionisation of liquid ammonia... 

An interesting historical application of the Boltzmann equation involves examination of the number density of very small spherical globules of latex suspended in water. The particles are dishibuted in the potential gradient of the gravitational field. If an arbitrary point in the suspension is selected, the number of particles N at height h pm (1 pm= 10 m) above the reference point can be counted with a magnifying lens. In one series of measurements, the number of particles per unit volume of the suspension as a function of h was as shown in Table 3-3. 

A reverse osmosis membrane acts as the semipermeable barrier to flow ia the RO process, aHowiag selective passage of a particular species, usually water, while partially or completely retaining other species, ie, solutes such as salts. Chemical potential gradients across the membrane provide the driving forces for solute and solvent transport across the membrane. The solute chemical potential gradient, —is usually expressed ia terms of concentration the water (solvent) chemical potential gradient, —Afi, is usually expressed ia terms of pressure difference across the membrane. 

Solution—Diffusion Model. In the solution—diffusion model, it is assumed that (/) the RO membrane has a homogeneous, nonporous surface layer (2) both the solute and solvent dissolve in this layer and then each diffuses across it (J) solute and solvent diffusion is uncoupled and each is the result of the particular material s chemical potential gradient across the membrane and (4) the gradients are the result of concentration and pressure differences across the membrane (26,30). The driving force for water transport is primarily a result of the net transmembrane pressure difference and can be represented by equation 5 ... 

In a high dielectric constant medium (i.e. water), when a potential gradient is established between an electrode and the solution a charge excess will develop on the electrode surface which must be balanced by solution species. Solvent molecules and other species (i.e. electrolyte) orient themselves at the electrode surface to counter the elec-... 

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