Biological Roles of the Elements
Classification of all 118 elements by their biological role in living organisms.
Essential: 12Essential (trace): 16Beneficial: 1Therapeutic use: 1Toxic: 19No biological role: 69
1HHydrogenEssentialComponent of water and all organic molecules. Makes up ~10% of body mass.2HeHeliumNo biological roleInert noble gas. Used in deep-sea diving gas mixtures.3LiLithiumTherapeutic useLithium salts used to treat bipolar disorder. No known biological role.4BeBerylliumToxicHighly toxic. Beryllium dust causes chronic beryllium disease (berylliosis).5BBoronEssential (trace)Needed for plant cell wall structure. Likely essential in trace amounts for animals.6CCarbonEssentialBackbone of all organic life. Forms proteins, DNA, carbohydrates, and lipids.7NNitrogenEssentialKey component of amino acids, nucleic acids, and ATP. Makes up ~3% of body mass.8OOxygenEssentialRequired for cellular respiration. Most abundant element in the human body by mass.9FFluorineEssential (trace)Strengthens tooth enamel as fluorapatite. Excess causes fluorosis.10NeNeonNo biological roleInert noble gas with no biological role.11NaSodiumEssentialMajor electrolyte. Essential for nerve impulses, muscle contraction, and fluid balance.12MgMagnesiumEssentialCofactor for 300+ enzymes. Required for ATP function, DNA synthesis, and muscle relaxation.13AlAluminumNo biological roleNo known biological role. Possible neurotoxin at high levels; debated link to Alzheimer's.14SiSiliconEssential (trace)Important for bone and connective tissue formation. Diatoms use it for their shells.15PPhosphorusEssentialComponent of DNA, RNA, ATP, and phospholipid cell membranes. ~1% of body mass.16SSulfurEssentialFound in amino acids methionine and cysteine. Essential for protein structure via disulfide bonds.17ClChlorineEssentialMajor electrolyte as chloride ion. Component of stomach acid (HCl).18ArArgonNo biological roleInert noble gas with no biological role.19KPotassiumEssentialMajor intracellular cation. Essential for nerve function, muscle contraction, and heart rhythm.20CaCalciumEssentialMain mineral in bones and teeth. Essential for muscle contraction, blood clotting, and signaling.21ScScandiumNo biological roleNo known biological role.22TiTitaniumNo biological roleNo known biological role. Biocompatible — used in surgical implants and dental prostheses.23VVanadiumEssential (trace)May be essential in very small amounts. Inhibits cholesterol synthesis in some organisms.24CrChromiumEssential (trace)Enhances insulin action in glucose metabolism. Required in microgram amounts.25MnManganeseEssential (trace)Cofactor for superoxide dismutase and other enzymes. Essential for bone formation.26FeIronEssentialCore of hemoglobin and myoglobin for oxygen transport. Deficiency causes anemia.27CoCobaltEssential (trace)Core of vitamin B₁₂ (cobalamin). Essential for DNA synthesis and red blood cell formation.28NiNickelEssential (trace)Essential for some plant enzymes (urease). May be required in trace amounts by animals.29CuCopperEssential (trace)Cofactor in cytochrome c oxidase, superoxide dismutase. Needed for iron metabolism.30ZnZincEssential (trace)Present in 300+ enzymes. Essential for immune function, wound healing, DNA synthesis, and taste.31GaGalliumNo biological roleNo known biological role. Gallium-67 used in medical imaging.32GeGermaniumNo biological roleNo confirmed biological role. Some dietary supplements claim health benefits (unproven).33AsArsenicToxicHighly toxic — disrupts ATP production. Chronic exposure causes arsenicosis. Historic poison.34SeSeleniumEssential (trace)Component of selenocysteine amino acid. Antioxidant role in glutathione peroxidase.35BrBromineEssential (trace)Required as bromide ion for collagen IV assembly in tissue development.36KrKryptonNo biological roleInert noble gas with no biological role.37RbRubidiumNo biological roleNo known biological role. Biochemically similar to potassium; used as tracer in studies.38SrStrontiumBeneficialStrontium ranelate used to treat osteoporosis. Incorporated into bone like calcium.39YYttriumNo biological roleNo known biological role. Yttrium-90 used in cancer radiotherapy.40ZrZirconiumNo biological roleNo known biological role. Biocompatible — used in dental implants.41NbNiobiumNo biological roleNo known biological role.42MoMolybdenumEssential (trace)Cofactor in xanthine oxidase, sulfite oxidase, and aldehyde oxidase enzymes.43TcTechnetiumNo biological roleRadioactive; no biological role. Tc-99m is the most used medical radioisotope for imaging.44RuRutheniumNo biological roleNo known biological role. Some ruthenium complexes studied as anticancer agents.45RhRhodiumNo biological roleNo known biological role.46PdPalladiumNo biological roleNo known biological role.47AgSilverNo biological roleNo known biological role. Has antimicrobial properties (oligodynamic effect).48CdCadmiumToxicHighly toxic. Accumulates in kidneys and liver. Causes itai-itai disease. Known carcinogen.49InIndiumNo biological roleNo known biological role.50SnTinEssential (trace)Possibly essential in trace amounts for rats. Used in dental amalgam historically.51SbAntimonyToxicToxic, similar to arsenic. Antimony compounds used medicinally for leishmaniasis.52TeTelluriumNo biological roleNo known biological role. Mildly toxic; causes garlic breath odor.53IIodineEssential (trace)Essential component of thyroid hormones (T₃, T₄). Deficiency causes goiter and cretinism.54XeXenonNo biological roleInert noble gas with no biological role. Xenon used as general anesthetic.55CsCesiumNo biological roleNo known biological role. Cs-137 is a dangerous radioactive contaminant.56BaBariumToxicBarium ions are toxic (block potassium channels). Barium sulfate used safely in medical imaging.57LaLanthanumNo biological roleNo known biological role. Low toxicity.58CeCeriumNo biological roleNo known biological role. Cerium oxide nanoparticles studied as antioxidants.59PrPraseodymiumNo biological roleNo known biological role.60NdNeodymiumNo biological roleNo known biological role. Low toxicity.61PmPromethiumNo biological roleRadioactive; no biological role.62SmSamariumNo biological roleNo known biological role. Sm-153 used in bone cancer pain treatment.63EuEuropiumNo biological roleNo known biological role.64GdGadoliniumNo biological roleNo known biological role. Gadolinium compounds used as MRI contrast agents.65TbTerbiumNo biological roleNo known biological role.66DyDysprosiumNo biological roleNo known biological role.67HoHolmiumNo biological roleNo known biological role.68ErErbiumNo biological roleNo known biological role.69TmThuliumNo biological roleNo known biological role. Tm-170 used in portable X-ray devices.70YbYtterbiumNo biological roleNo known biological role.71LuLutetiumNo biological roleNo known biological role. Lu-177 used in cancer radiotherapy.72HfHafniumNo biological roleNo known biological role. Very low toxicity.73TaTantalumNo biological roleNo known biological role. Biocompatible; used in surgical implants.74WTungstenEssential (trace)Essential cofactor in some bacterial and archaeal enzymes (tungstoenzymes).75ReRheniumNo biological roleNo known biological role. Re-186 and Re-188 used in cancer radiotherapy.76OsOsmiumToxicOsmium tetroxide (OsO₄) is highly toxic and a powerful oxidizer. Metal form is less dangerous.77IrIridiumNo biological roleNo known biological role. Iridium-rich clay layer marks the K-Pg extinction event.78PtPlatinumNo biological roleNo known biological role. Cisplatin (Pt complex) is a key chemotherapy drug.79AuGoldNo biological roleNo known biological role. Biologically inert. Gold compounds used to treat rheumatoid arthritis.80HgMercuryToxicHighly toxic, especially as methylmercury. Bioaccumulates in food chains. Damages nervous system.81TlThalliumToxicExtremely toxic — 'poisoner\'s poison.' Causes alopecia. Tl-201 used in cardiac imaging.82PbLeadToxicNeurotoxin, especially harmful to children. Causes lead poisoning. No safe exposure level.83BiBismuthNo biological roleLow toxicity for a heavy metal. Bismuth subsalicylate (Pepto-Bismol) treats digestive issues.84PoPoloniumToxicExtremely radioactive and toxic. Famously used to poison Alexander Litvinenko in 2006.85AtAstatineNo biological roleExtremely rare and radioactive. No biological role.86RnRadonToxicRadioactive noble gas. Second leading cause of lung cancer after smoking.87FrFranciumNo biological roleExtremely radioactive and rare. No biological role.88RaRadiumToxicRadioactive. Mimics calcium and incorporates into bones, causing bone cancer.89AcActiniumNo biological roleRadioactive. Ac-225 studied for targeted alpha therapy against cancer.90ThThoriumToxicWeakly radioactive. Can cause liver and bone damage if inhaled or ingested.91PaProtactiniumToxicRadioactive and toxic. No biological role.92UUraniumToxicRadioactive and chemically toxic to kidneys. Depleted uranium used in armor-piercing munitions.93NpNeptuniumToxicSynthetic, radioactive. No biological role. Trace amounts from nuclear reactors.94PuPlutoniumToxicExtremely toxic due to radioactivity. Alpha emitter that concentrates in bone.95AmAmericiumToxicRadioactive. Used in smoke detectors (Am-241). Alpha emitter.96CmCuriumToxicRadioactive. Cm-244 used as power source in space probes.97BkBerkeliumNo biological roleSynthetic, radioactive element. No biological role.98CfCaliforniumNo biological roleSynthetic, radioactive element. No biological role.99EsEinsteiniumNo biological roleSynthetic, radioactive element. No biological role.100FmFermiumNo biological roleSynthetic, radioactive element. No biological role.101MdMendeleviumNo biological roleSynthetic, radioactive element. No biological role.102NoNobeliumNo biological roleSynthetic, radioactive element. No biological role.103LrLawrenciumNo biological roleSynthetic, radioactive element. No biological role.104RfRutherfordiumNo biological roleSynthetic, radioactive element. No biological role.105DbDubniumNo biological roleSynthetic, radioactive element. No biological role.106SgSeaborgiumNo biological roleSynthetic, radioactive element. No biological role.107BhBohriumNo biological roleSynthetic, radioactive element. No biological role.108HsHassiumNo biological roleSynthetic, radioactive element. No biological role.109MtMeitneriumNo biological roleSynthetic, radioactive element. No biological role.110DsDarmstadtiumNo biological roleSynthetic, radioactive element. No biological role.111RgRoentgeniumNo biological roleSynthetic, radioactive element. No biological role.112CnCoperniciumNo biological roleSynthetic, radioactive element. No biological role.113NhNihoniumNo biological roleSynthetic, radioactive element. No biological role.114FlFleroviumNo biological roleSynthetic, radioactive element. No biological role.115McMoscoviumNo biological roleSynthetic, radioactive element. No biological role.116LvLivermoriumNo biological roleSynthetic, radioactive element. No biological role.117TsTennessineNo biological roleSynthetic, radioactive element. No biological role.118OgOganessonNo biological roleSynthetic, radioactive element. No biological role.