calcium phosphate. Fe2+/Fe3+as found in haemoglobin, the main oxygen carrying molecule has a central iron ion. source of nitrogen in plants for the synthesis of proteins. Biological functions of inorganic ions Ion channels K+ channels Potassium ion channels play a key role in maintaining the membrane's electric potential. These ion channels are present in many various biological systems. They frequently play a role in regulation of cellular level processes, many of these processes including muscle relaxation, hypertension, insulin secretion etc. Some examples of potassium ion channels within biological systems include KATP channels, BK channels, and ether-a-go-go potassium channels Na+ channels Sodium ion channels provide an integral service through the body, as they transmit depolarizing impulses at the cellular and intracellular level. This allows sodium ions to coordinate much more intensive processes such as movement and cognition. Sodium ion channels consist of various subunits, however, only the principle subunit is required for function. These sodium ion channels consist of four internally homologous domains, each of which containing six transmembrane segments and resembling a single subunit of a voltage-dependent potassium ion channel. The four domains fold together, forming a central pore. That central pore of the sodium ions dictates the selectivity of the channel: both ionic radius and ionic charge are key in channel selectivity. Cl− channels Chloride ion channels vary from many other ion channels due to being controlled by the anionic chloride ions. Chloride ion channels are pore-forming membrane proteins that allow the passive transport of chloride ions across biological membranes. Chloride ion channels involve both voltage-gated and ligand-gated mechanisms to transport the ions across cellular membranes. Chloride ion channels have been found to play crucial roles in the development of human diseases, for example, mutations in the genes encoding chloride ion channels lead to a variety of deleterious diseases in muscle, kidney, bone, and brain, including cystic fibrosis, osteoporosis, and epilepsy, and similarly their activation is supposed to be responsible for the progression of glioma in the brain and the growth of malaria-parasite in the red blood cells. Currently, chloride ion channels are not completely understood, and more research is necessary. See also Calcium in biology Magnesium in biology Inorganic anions in biology Phosphate in biology Chloride in biology References Ions Cell biology Signal transduction