Biometals are metals normally present, in small but important and measurable amounts, in biology, biochemistry, and medicine. The metals copper, zinc, iron, and manganese are examples of metals that are essential for the normal functioning of most plants and the bodies of most animals, such as the human body. A few (calcium, potassium, sodium) are present in relatively larger amounts, whereas most others are trace metals, present in smaller but important amounts (the image shows the percentages for humans). Approximately 2/3 of the existing periodic table is composed of metals with varying properties, accounting for the diverse ways in which metals (usually in ionic form) have been utilized in nature and medicine. History At first, the study of biometals was referred to as bioinorganic chemistry. Each branch of bioinorganic chemistry studied separate, particular sub-fields of the subject. However, this led to an isolated view of each particular aspect in a biological system. This view was revised into a holistic approach of biometals in metallomics. Metal ions in biology were studied in various specializations. In nutrition, it was to define the essentials for life; in toxicology, to define how the adverse effects of certain metal ions in biological systems and in pharmacology for their therapeutic effects. In each field, at first, they were studied and separated on a basis of concentration. In low amounts, metal ions in a biological system could perform at their optimal functionality whereas in higher concentrations, metal ions can prove fatal to biological systems. However, the concentration gradients were proved to be arbitrary as low concentrations of non-essential metals (like lithium or helium) in essential metals (like sodium or potassium) can cause an adverse effect in biological systems and vice versa. Investigations into biometals and their effects date back to the 19th century and even further back to the 18th century with the identification of iron in blood. Zinc was identified to be essential in fungal growth of yeast as shown by Jules Raulin in 1869 yet no proof for the need of zinc in human cells was shown until the late 1930s where its presence was demonstrated in carbonic anhydrase and the 1960s where it was identified as a necessary element for humans. Since then, understanding of zinc in human biology has advanced to the point that it is considered as important as iron. Modern advancements in analytical technology have made it clear the importance of