Biological exchange process

Biological exchange processes in the forest canopy are absorption or leaching, e.g., irreversible stomata uptake or leaching of elements originating from root uptake. 

Adsorption by a solid surface of a solute hi dilute solution is of course the basis of many technical operations, e.g. clarification of industrial liquors, detergency, dyeing, lubrication, tanning, and numerous ion-exchange processes, and is probably operative in most biological systems. 

Brunke, M., and T. Gonser. 1997. The ecological significance of exchange processes between rivers and groundwater. Freshwater Biology 37 1-33. 

In the earlier discussion of the effects of dynamic processes on NMR spectra of small molecules (Chapter 10), the NMR time scale for the exchange process was determined by the relationship between the preexchange lifetimes (or the inverse rate constants) and the chemical shift difference between the two states (or sites). This is also true for many systems of biological importance when the line widths of the resonances... 

Figure 10 Solid-water exchange processes in groundwater and surface-water environments illustrating sorption to particulates (iG) and biological concentration factor (BCF). Retardation in groundwater aquifer signified by the difference between water and compound velocities (U) (after Schwarzenbach et al., 1998).

Table 15.4 gives a rough mass balance of riverine inputs and the various outputs by atmospheric cycling, ion exchange processes, deposition in sediments, and hydrothermal activities. One important part of the mass balance is the deposition of CaCOs. Biological processes also cause the removal of S04, which is consumed in biologically mediated sulfate reduction and deposited as pyrite. 

Geochemically significant mixing and transport can sometimes be accomplished by biological processes. An interesting example is redistribution of sediment material caused by the movements of worms and other organisms (bioturbation). Exchange processes between the atmosphere and oceans and between the oceans and the sediments are treated below in separate sections. 

Knowledge of the size of the exchangeable pool of lipid in a substrate is necessary to determine the rate constants of the exchange process and establish the specificity of a transfer protein for different classes of phospholipids. The size of the exchangeable pool of each class of phospholipid must be determined individually because phospholipids are often asymmetrically distributed across biological and artificial membranes (Op den Kamp, 1979). 

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