chemical elements constantly present in organisms and having definite biological significance. They include, above all, oxygen (constituting 70 percent of
|Table 1. Average content of chemical elements in organisms (mg per 100 g of dry substance; after Bowen, 1966)|
|Au||0.0012||< 0.00005–0.0002||0.00003–0.0008||0.000023 (?)||—|
|Table 2. Content of chemical elements In mammals|
|Content ot elements (percent ot dry substance; order of magnitude)||(1) Irreplaceable||(2) role not fully ascertained||(3) role unknown|
|101-10-0||0, C, H, N, Ca|
|100-10-1||P, K, CI, S, Na|
|10-3-10-4||Cu||Cd, Br||Li, Cs|
|10-4-10-5||Mn, V||B, Si||Al, Ba, Cr|
|10-5-10-6||Co||Ni||Ga, Ce, As, Hg,|
|Pb, Bi, Ti|
the mass of organisms), carbon (18 percent), hydrogen (10 percent), calcium, nitrogen, potassium, phosphorus, magnesium, sulfur, chlorine, sodium, and iron. These elements are part of all living organisms and make up their main mass while performing a major role in the vital processes. Advances in analytical chemistry and spectral analysis have extended the list of biogenic elements. Scientists are continually finding new elements present in small amounts in organisms (trace elements) and discovering the biological role of many of them. V. I. Vernadskii considered that all the chemical elements constantly present in cells and tissues of organisms under natural conditions probably play a specific physiological role. Many elements are highly important only for certain groups of living things (for example, boron is essential for plants, vanadium for ascidians, and so on). The amount of any given elements in organisms depends both on their species characteristics and on the composition of the medium, the diet (particularly, for plants, the concentration and solubility of various soil salts), the ecological characteristics of the organism, and other factors (see Table 1). If some biogenic element is prevented from entering the organism, disease results (biogeochemical endemics—for example, goiter in man if there is a deficiency of iodine in the water and diet or black spot of beets if there is a deficiency of boron). The elements constantly present in mammals can be divided into three groups according to what is known about them and their importance (see Table 2): (1) elements that are part of biologically active compounds (enzymes, hormones, vitamins, or pigments) and are irreplaceable; (2) elements whose physiological and biochemical role has not been fully ascertained; and (3) elements whose role is unknown.
Some other chemical elements are also found in organisms, but their concentration in the tissues and organs and their biological role have not been studied.
V. V. KOVAL’SKII