Essential elements, in biological systems

Unlike the metals, the chemistry of these elements is diverse. Despite their relatively small number, most of the essential elements IN BIOLOGICAL SYSTEMS ARE NONMETALS (O, C, H, N, P, AND S). This group also includes the most unreactive elements—the... 

Of the 117 elements known, only 25 are nonmetallic elements. Unlike the metals, the chemistry of these elements is diverse. Despite their relatively small number, most of the essential elements in biological systems are nonmetals (H, C, N, P, O, S, Cl, and I). This group of nonmetallic elements also includes the most unreactive of the elements—the noble gases. The unique properties of hydrogen set it aside from the rest of the elements in the periodic table. A whole branch of chemistry—organic chemistry—is based on carbon compounds. 

It is impossible to cover adequately the chemistry of various elements in biological systems in a single chapter. Before discussing the salient points of other essential and trace elements, the biochemistry of iron will be discussed briefly. Iron is the most... 

Many of the non metals such as hydrogen, carbon, nitrogen, oxygen, phosphorus, sulfur, chlorine, and iodine are essential elements, and most are used in quantities for beyond the trace levels. Nevertheless, most of the chemistry of these elements in biological systems is more closely associated with organic chemistry than with inorganic chemistry. 

Iron enjoys a unique position as an essential trace element in biological systems. By virtue of its role in electron transfer it is generally present in higher concentration than the other trace elements. At the same time its extreme insolubility at physiological pH and the myriad of reaction... 

In recent studies vanadium has been shown to be an essential requirement in biological systems, and the chemistry of the element is... 

Change in the oxidation state of an element can have a profound effect on bioavailability and toxicity. Fe(II) is biologically the main usable form of iron, Fe(III) in excess can cause stomach lesions.When chromium appears as a pollutant in a sample of river water or in a Cr complex dye, its valency is of relevance in ascertaining the relative toxicity of the sample. Trivalent chromium is an essential element in mammalian systems, hexavalent chromium is considered to be a moderate to severe industrial hazard. 

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