Metabolism composition, variation

Recognition among bone-chemistry researchers that strontium enters bone in proportion to dietary levels has resulted in widely accepted yet erroneous inferences about the relationships among various elements in bone and past diet. One such inference is that more of any element in the diet translates directly to more of that element in bone. If an element is not biogenically incorporated within bone, or if biological levels are metabolically controlled, then that element will not reflect diet. A second erroneous inference is that strontium can be used to measure the dietary plant/meat ratio. Sr/Ca ratios in meat are generally lower than those of plants, but meat is also low in calcium and hence has little effect on the composition of bone. Plants, on the other hand, contribute substantially to bone composition. Variations in the strontium levels of bone thus more likely reflect differential consumption of plants rather than trophic position. Although efforts to determine plant/meat ratios from strontium and to draw dietary inferences from elements other than strontium and barium have not been successful, this failure has been due to inappropriate expectations, not to a failure of bone strontium to reflect diet. 

In summary, microbial life is influenced by many parameters. Adaptation to a change is possible [13,26], This allows microorganisms to be present wherever a substrate is available for metabolism. A variation in the parameters previously mentioned may be used to control microbial growth. However, care must be taken to ensure that merely adaptation of the microorganisms present and not a change in the composition of the microbial biocoenosis takes place. 

Analyses of PCBs can create large data sets that are difficult to interpret, since there are 209 PCB isomers. Isomer compositions may vary widely due to differential partitioning or metabolism of compounds. In addition, wide differences in residue profiles may exist in the biota locally because of variations in effluents, combustion, or other source of residues. Chemometric methods can... 

Studies of the respiratory quotient or respiratory exchange ratio (RER) indicate a metabolic shift in CR rats depending on food availability, while there is little change in AL rats [21,42]. Figure 7 illustrates daily variations of RER with dietary regimen. Analysis of the food composition indicates an expected average value of RER of 0.89. RER in AL rats is 0.89 0.02 over a 24-hour period and is relatively more constant than that in CR rats, indicating that AL rats metabolize a constant ratio of carbohydrate and lipid over 24 hours [21, 42]. In contrast, CR animals metabolize more carbohydrate... 

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