Composition of the human body

Body composition may be analyzed in terms of molecular type e.g., water, protein, connective tissue, fats (or lipids), hydroxylapatite (in bones), carbohydrates (such as glycogen and glucose) and DNA. In terms of tissue type, the body may be analyzed into water, fat, muscle, bone, etc. In terms of cell type, the body contains hundreds of different types of cells, but notably, the largest number of cells contained in a human body (though not the largest mass of cells) are not human cells, but bacteria residing in the normal human gastrointestinal tract.

The main elements that compose the human body are shown from most abundant (by mass, not by fraction of atoms) to least abundant.
201 Elements of the Human Body.02 Element Symbol % in body
Oxygen O 65.0
Carbon C 18.5
Hydrogen H 9.5
Nitrogen N 3.2
Calcium Ca 1.5
Phosphorus P 1.0
Potassium K 0.4
Sulfur S 0.3
Sodium Na 0.2
Chlorine Cl 0.2
Magnesium Mg 0.2
Trace elements including boron (B), chromium (Cr), cobalt (Co), copper (Cu), fluorine (F), iodine (I), iron (Fe), manganese (Mn), molybdenum (Mo), selenium (Se), silicon (Si), tin (Sn), vanadium (V), and zinc (Zn). < 1.0


Two pie graphs about the composition of the human body
Pie charts of typical human body composition by percent of mass, and by percent of atomic composition (atomic percent).

Almost 99% of the mass of the human body is made up of six elements: oxygen, carbon, hydrogen, nitrogen, calcium, and phosphorus. Only about 0.85% is composed of another five elements: potassium, sulfur, sodium, chlorine, and magnesium. All 11 are necessary for life. The remaining elements are trace elements, of which more than a dozen are thought on the basis of good evidence to be necessary for life. All of the mass of the trace elements put together (less than 10 grams for a human body) do not add up to the body mass of magnesium, the least common of the 11 non-trace elements.

Other elements

Not all elements which are found in the human body in trace quantities play a role in life. Some of these elements are thought to be simple bystander contaminants without function (examples: caesium, titanium), while many others are thought to be active toxics, depending on amount (cadmium, mercury, radioactives). The possible utility and toxicity of a few elements at levels normally found in the body (aluminium) is debated. Functions have been proposed for trace amounts of cadmium and lead, although these are almost certainly toxic in amounts very much larger than normally found in the body. There is evidence that arsenic, an element normally considered a toxin in higher amounts, is essential in ultratrace quantities, in mammals such as rats, hamsters, and goats.[1]

Some elements (silicon, boron, nickel, vanadium) are probably needed by mammals also, but in far smaller doses. Bromine is used abundantly by some (though not all) lower organisms, and opportunistically in eosinophils in humans. One study has found bromine to be necessary to collagen IV synthesis in humans.[2] Fluorine is used by a number of plants to manufacture toxins (see that element) but in humans only functions as a local (topical) hardening agent in tooth enamel, and not in an essential biological role.[3]

Elemental composition list

The average 70 kg (150 lb) adult human body contains approximately 7×1027 atoms and contains at least detectable traces of 60 chemical elements.[4] About 29 of these elements are thought to play an active positive role in life and health in humans.[5]

The relative amounts of each element vary by individual, mainly due to differences in the proportion of fat, muscle and bone in their body. Persons with more fat will have a higher proportion of carbon and a lower proportion of most other elements (the proportion of hydrogen will be about the same). The numbers in the table are averages of different numbers reported by different references.

The adult human body averages ~53% water.[6] This varies substantially by age, sex, and adiposity. In a large sample of adults of all ages and both sexes, the figure for water fraction by weight was found to be 48 ±6% for females and 58 ±8% water for males.[7] Water is ~11% hydrogen by mass but ~67% hydrogen by atomic percent, and these numbers along with the complementary % numbers for oxygen in water, are the largest contributors to overall mass and atomic composition figures. Because of water content, the human body contains more oxygen by mass than any other element, but more hydrogen by atom-fraction than any element.

The elements listed below as "Essential in humans" are those listed by the (US) Food and Drug Administration as essential nutrients,[8] as well as six additional elements: oxygen, carbon, hydrogen, and nitrogen (the fundamental building blocks of life on Earth), sulfur (essential to all cells) and cobalt (a necessary component of vitamin B12). Elements listed as "Possibly" or "Probably" essential are those cited by the National Research Council (United States) as beneficial to human health and possibly or probably essential.[9]

Atomic number Element Fraction of mass[10][11][12][13][14][15] Mass (kg)[16] Atomic percent Essential in humans[17] Negative effects of excess Group
8 Oxygen 0.65 43 24 Yes (e.g. water, electron acceptor)[18] Reactive oxygen species 16
6 Carbon 0.18 16 12 Yes[18] (organic compounds) 14
1 Hydrogen 0.10 7 62 Yes[18] (e.g. water) 1
7 Nitrogen 0.03 1.8 1.1 Yes[18] (e.g. DNA and amino acids) 15
20 Calcium 0.014 1.0 0.22 Yes[18][19][20] (e.g. Calmodulin and Hydroxylapatite in bones) 2
15 Phosphorus 0.011 0.78 0.22 Yes[18][19][20] (e.g. DNA and phosphorylation) white allotrope highly toxic 15
19 Potassium 2.0×10−3 0.14 0.033 Yes[18][19] (e.g. Na+/K+-ATPase) 1
16 Sulfur 2.5×10−3 0.14 0.038 Yes[18] (e.g. Cysteine, Methionine, Biotin, Thiamine) 16
11 Sodium 1.5×10−3 0.10 0.037 Yes[19] (e.g. Na+/K+-ATPase) 1
17 Chlorine 1.5×10−3 0.095 0.024 Yes[19][20] (e.g. Cl-transporting ATPase) 17
12 Magnesium 500×10−6 0.019 0.0070 Yes[19][20] (e.g. binding to ATP and other nucleotides) 2
26 Iron* 60×10−6 0.0042 0.00067 Yes[19][20] (e.g. Hemoglobin, Cytochromes) 8
9 Fluorine 37×10−6 0.0026 0.0012 Yes (AUS, NZ),[21] No (US, EU),[22][23] Maybe (WHO)[24] toxic in high amounts 17
30 Zinc 32×10−6 0.0023 0.00031 Yes[19][20] (e.g. Zinc finger proteins) 12
14 Silicon 20×10−6 0.0010 0.0058 Possibly[9] 14
37 Rubidium 4.6×10−6 0.00068 0.000033 No 1
38 Strontium 4.6×10−6 0.00032 0.000033 —— 2
35 Bromine 2.9×10−6 0.00026 0.000030 —— 17
82 Lead 1.7×10−6 0.00012 0.0000045 No toxic 14
29 Copper 1×10−6 0.000072 0.0000104 Yes[19][20] (e.g. copper proteins) 11
13 Aluminium 870×10−9 0.000060 0.000015 No 13
48 Cadmium 720×10−9 0.000050 0.0000045 No toxic 12
58 Cerium 570×10−9 0.000040 No
56 Barium 310×10−9 0.000022 0.0000012 No toxic in higher amounts 2
50 Tin 240×10−9 0.000020 6.0×10−7 No 14
53 Iodine 160×10−9 0.000020 7.5×10−7 Yes[19][20] (e.g. thyroxine, triiodothyronine) 17
22 Titanium 130×10−9 0.000020 No 4
5 Boron 690×10−9 0.000018 0.0000030 Probably[9][25] 13
34 Selenium 190×10−9 0.000015 4.5×10−8 Yes[19][20] toxic in higher amounts 16
28 Nickel 140×10−9 0.000015 0.0000015 Probably[9][25] toxic in higher amounts 10
24 Chromium 24×10−9 0.000014 8.9×10−8 Yes[19][20] 6
25 Manganese 170×10−9 0.000012 0.0000015 Yes[19][20] (e.g. Mn-SOD) 7
33 Arsenic 260×10−9 0.000007 8.9×10−8 Possibly[1][9] toxic in higher amounts 15
3 Lithium 31×10−9 0.000007 0.0000015 Yes (intercorrelated with the functions of several enzymes, hormones and vitamins) toxic in higher amounts 1
80 Mercury 190×10−9 0.000006 8.9×10−8 No toxic 12
55 Caesium 21×10−9 0.000006 1.0×10−7 No 1
42 Molybdenum 130×10−9 0.000005 4.5×10−8 Yes[19][20] (e.g. the molybdenum oxotransferases, Xanthine oxidase and Sulfite oxidase) 6
32 Germanium 5×10−6 No 14
27 Cobalt 21×10−9 0.000003 3.0×10−7 Yes (cobalamin, B12)[26][27] 9
51 Antimony 110×10−9 0.000002 No toxic 15
47 Silver 10×10−9 0.000002 No 11
41 Niobium 1600×10−9 0.0000015 No 5
40 Zirconium 6×10−6 0.000001 3.0×10−7 No 4
57 Lanthanum 1370×10−9 8×10−7 No
52 Tellurium 120×10−9 7×10−7 No 16
31 Gallium 7×10−7 No 13
39 Yttrium 6×10−7 No 3
83 Bismuth 5×10−7 No 15
81 Thallium 5×10−7 No highly toxic 13
49 Indium 4×10−7 No 13
79 Gold 3×10−9 2×10−7 3.0×10−7 No uncoated nanoparticles possibly genotoxic[28][29][30] 11
21 Scandium 2×10−7 No 3
73 Tantalum 2×10−7 No 5
23 Vanadium 260×10−9 1.1×10−7 1.2×10−8 Possibly[9] (suggested osteo-metabolism (bone) growth factor) 5
90 Thorium 1×10−7 No toxic, radioactive
92 Uranium 1×10−7 3.0×10−9 No toxic, radioactive
62 Samarium 5.0×10−8 No
74 Tungsten 2.0×10−8 No 6
4 Beryllium 3.6×10−8 4.5×10−8 No toxic in higher amounts 2
88 Radium 3×10−14 1×10−17 No toxic, radioactive 2

*Iron = ~3 g in men, ~2.3 g in women

Of the 94 naturally occurring chemical elements, 60 are listed in the table above. Of the remaining 34, it is not known how many occur in the human body.

Most of the elements needed for life are relatively common in the Earth's crust. Aluminium, the third most common element in the Earth's crust (after oxygen and silicon), serves no function in living cells, but is harmful in large amounts.[31] Transferrins can bind aluminium.[32]

Periodic table

Nutritional elements in the periodic table
H   He
Li Be   B C N O F Ne
Na Mg   Al Si P S Cl Ar
K Ca Sc   Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr
Rb Sr Y   Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe
Cs Ba La * Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn
Fr Ra Ac ** Rf Db Sg Bh Hs Mt Ds Rg Cn Nh Fl Mc Lv Ts Og
  * Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu
  ** Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No Lr
  Quantity elements
  Essential trace elements
  Deemed essential trace element by U.S., not by European Union
  Suggested function from deprivation effects or active metabolic handling, but no clearly-identified biochemical function in humans
  Limited circumstantial evidence for trace benefits or biological action in mammals
  No evidence for biological action in mammals, but essential in some lower organisms.
(In the case of lanthanum, the definition of an essential nutrient as being indispensable and irreplaceable is not completely applicable due to the extreme similarity of the lanthanides. Thus Ce, Pr, and Nd may be substituted for La without ill effects for organisms using La, and the smaller Sm, Eu, and Gd may also be similarly substituted but cause slower growth.)


The composition of the human body is expressed in terms of chemicals:

The composition of the human body can be viewed on an atomic and molecular scale as shown in this article.

The estimated gross molecular contents of a typical 20-micrometre human cell is as follows:[34]

Molecule Percent of Mass Mol.Weight (daltons) Molecules Percent of Molecules
Water 65 18 1.74×1014 98.73
Other Inorganics 1.5 N/A 1.31×1012 0.74
Lipids 12 N/A 8.4×1011 0.475
Other Organics 0.4 N/A 7.7×1010 0.044
Protein 20 N/A 1.9×1010 0.011
RNA 1.0 N/A 5×107 3×10−5
DNA 0.1 1×1011 46* 3×10−11


Body composition can also be expressed in terms of various types of material, such as:

Composition by cell type

There are many species of bacteria and other microorganisms that live on or inside the healthy human body. In fact, 90% of the cells in (or on) a human body are microbes, by number[35][36] (much less by mass or volume). Some of these symbionts are necessary for our health. Those that neither help nor harm humans are called commensal organisms.

See also


  1. ^ a b Anke M. "Arsenic". In: Mertz W. ed., Trace elements in human and Animal Nutrition, 5th ed. Orlando, FL: Academic Press, 1986, 347-372; Uthus E. O., "Evidency for arsenical essentiality", Environmental Geochemistry and Health, 1992, 14:54-56; Uthus E.O., Arsenic essentiality and factors affecting its importance. In: Chappell W. R., Abernathy C. O., Cothern C. R. eds., Arsenic Exposure and Health. Northwood, UK: Science and Technology Letters, 1994, 199-208.
  2. ^ McCall AS, Cummings CF, Bhave G, Vanacore R, Page-McCaw A, Hudson BG (2014). "Bromine Is an Essential Trace Element for Assembly of Collagen IV Scaffolds in Tissue Development and Architecture". Cell. 157 (6): 1380–92. doi:10.1016/j.cell.2014.05.009. PMC 4144415. PMID 24906154.
  3. ^ Nelson, Lehninger, Cox (2008). Lehninger Principles of Biochemistry (5th ed.). Macmillan.CS1 maint: Multiple names: authors list (link)
  4. ^ How many atoms are in the human body?
  5. ^ "Ultratrace minerals". Authors: Nielsen, Forrest H. USDA, ARS Source: Modern nutrition in health and disease / editors, Maurice E. Shils ... et al.. Baltimore : Williams & Wilkins, c. 1999, p. 283-303. Issue Date: 1999 URI: [1]
  6. ^ Use WP:CALC for the mean of means for males and females, since the two groups are of about equal size
  7. ^ See table 1. here
  8. ^ "Guidance for Industry: A Food Labeling Guide 14. Appendix F"
  9. ^ a b c d e f Institute of Medicine (29 September 2006). Dietary Reference Intakes: The Essential Guide to Nutrient Requirements. National Academies Press. pp. 313–19, 415–22. ISBN 978-0-309-15742-1. Retrieved 21 June 2016.
  10. ^ Thomas J. Glover, comp., Pocket Ref, 3rd ed. (Littleton: Sequoia, 2003), p. 324 (LCCN 2002-91021), which in
  11. ^ turn cites Geigy Scientific Tables, Ciba-Geigy Limited, Basel, Switzerland, 1984.
  12. ^ Chang, Raymond (2007). Chemistry, Ninth Edition. McGraw-Hill. p. 52. ISBN 978-0-07-110595-8.
  13. ^ "Elemental Composition of the Human Body" by Ed Uthman, MD Retrieved 17 June 2016
  14. ^ Frausto Da Silva, J. J. R; Williams, R. J. P (2001-08-16). The Biological Chemistry of the Elements: The Inorganic Chemistry of Life. ISBN 9780198508489.
  15. ^ Zumdahl, Steven S. and Susan A. (2000). Chemistry, Fifth Edition. Houghton Mifflin Company. p. 894. ISBN 978-0-395-98581-6.)
  16. ^ Emsley, John (25 August 2011). Nature's Building Blocks: An A-Z Guide to the Elements. OUP Oxford. p. 83. ISBN 978-0-19-960563-7. Retrieved 17 June 2016.
  17. ^ Neilsen, cited
  18. ^ a b c d e f g h Salm, Sarah; Allen, Deborah; Nester, Eugene; Anderson, Denise (9 January 2015). Nester's Microbiology: A Human Perspective. p. 21. ISBN 978-0-07-773093-2. Retrieved 19 June 2016.
  19. ^ a b c d e f g h i j k l m n Subcommittee on the Tenth Edition of the Recommended Dietary Allowances, Food and Nutrition Board; Commission on Life Sciences, National Research Council (1 February 1989). "9-10". Recommended Dietary Allowances: 10th Edition. National Academies Press. ISBN 978-0-309-04633-6. Retrieved 18 June 2016.
  20. ^ a b c d e f g h i j k l Code of Federal Regulations, Title 21: Food and Drugs, Ch 1, subchapter B, Part 101, Subpart A, §101.9(c)(8)(iv)
  21. ^ Australian National Health and Medical Research Council (NHMRC) and New Zealand Ministry of Health (MoH)
  22. ^ "Fluoride in Drinking Water: A Review of Fluoridation and Regulation Issues"
  23. ^ "Scientific Opinion on Dietary Reference Values for fluoride". EFSA Journal. 11 (8): 3332. 2013. doi:10.2903/j.efsa.2013.3332. ISSN 1831-4732.
  24. ^ WHO/SDE/WSH/03.04/96 "Fluoride in Drinking-water"
  25. ^ a b Safe Upper Levels for Vitamins and Mineral (2003), boron p. 164-71, nickel p. 225-31, EVM, Food Standards Agency, UK ISBN 1-904026-11-7
  26. ^ Yamada, Kazuhiro (2013). Cobalt: Its Role in Health and Disease. Metal Ions in Life Sciences. 13. pp. 295–320. doi:10.1007/978-94-007-7500-8_9. ISBN 978-94-007-7499-5. ISSN 1559-0836. PMID 24470095.
  27. ^ Banci, Lucia (18 April 2013). Metallomics and the Cell. Springer Science & Business Media. pp. 333–368. ISBN 978-94-007-5561-1. Retrieved 19 June 2016.
  28. ^ Fratoddi, Ilaria; Venditti, Iole; Cametti, Cesare; Russo, Maria Vittoria (2015). "How toxic are gold nanoparticles? The state-of-the-art". Nano Research. 8 (6): 1771–1799. doi:10.1007/s12274-014-0697-3. ISSN 1998-0124.
  29. ^ "Scientific Opinion on the re-evaluation of gold (E 175) as a food additive". EFSA Journal. 14 (1): 4362. 2016. doi:10.2903/j.efsa.2016.4362. ISSN 1831-4732.
  30. ^ Hillyer, Julián F.; Albrecht, Ralph M. (2001). "Gastrointestinal persorption and tissue distribution of differently sized colloidal gold nanoparticles". Journal of Pharmaceutical Sciences. 90 (12): 1927–1936. doi:10.1002/jps.1143. ISSN 0022-3549.
  31. ^ Aluminum Toxicity
  32. ^ Mizutani, K.; Mikami, B.; Aibara, S.; Hirose, M. (2005). "Structure of aluminium-bound ovotransferrin at 2.15 Å resolution". Acta Crystallographica Section D. 61 (12): 1636. doi:10.1107/S090744490503266X.
  33. ^ Douglas Fox, "The speed of life", New Scientist, No 2419, 1 November 2003.
  34. ^ Freitas Jr., Robert A. (1999). Nanomedicine. Landes Bioscience. Tables 3–1 & 3–2. ISBN 978-1-57059-680-3.
  35. ^ Glausiusz, Josie. "Your Body Is a Planet". Retrieved 2007-09-16.
  36. ^ Wenner, Melinda. "Humans Carry More Bacterial Cells than Human Ones". Retrieved 2010-10-09.

Biochemistry, sometimes called biological chemistry, is the study of chemical processes within and relating to living organisms. Biochemical processes give rise to the complexity of life.

A sub-discipline of both biology and chemistry, biochemistry can be divided in three fields; molecular genetics, protein science and metabolism. Over the last decades of the 20th century, biochemistry has through these three disciplines become successful at explaining living processes. Almost all areas of the life sciences are being uncovered and developed by biochemical methodology and research. Biochemistry focuses on understanding how biological molecules give rise to the processes that occur within living cells and between cells, which in turn relates greatly to the study and understanding of tissues, organs, and organism structure and function.Biochemistry is closely related to molecular biology, the study of the molecular mechanisms by which genetic information encoded in DNA is able to result in the processes of life.Much of biochemistry deals with the structures, functions and interactions of biological macromolecules, such as proteins, nucleic acids, carbohydrates and lipids, which provide the structure of cells and perform many of the functions associated with life. The chemistry of the cell also depends on the reactions of smaller molecules and ions. These can be inorganic, for example water and metal ions, or organic, for example the amino acids, which are used to synthesize proteins. The mechanisms by which cells harness energy from their environment via chemical reactions are known as metabolism. The findings of biochemistry are applied primarily in medicine, nutrition, and agriculture. In medicine, biochemists investigate the causes and cures of diseases. In nutrition, they study how to maintain health wellness and study the effects of nutritional deficiencies. In agriculture, biochemists investigate soil and fertilizers, and try to discover ways to improve crop cultivation, crop storage and pest control.

Biological organisation

Biological organization is the hierarchy of complex biological structures and systems that define life using a reductionistic approach. The traditional hierarchy, as detailed below, extends from atoms to biospheres. The higher levels of this scheme are often referred to as an ecological organization concept, or as the field, hierarchical ecology.

Each level in the hierarchy represents an increase in organizational complexity, with each "object" being primarily composed of the previous level's basic unit. The basic principle behind the organization is the concept of emergence—the properties and functions found at a hierarchical level are not present and irrelevant at the lower levels.

The biological organization of life is a fundamental premise for numerous areas of scientific research, particularly in the medical sciences. Without this necessary degree of organization, it would be much more difficult—and likely impossible—to apply the study of the effects of various physical and chemical phenomena to diseases and physiology (body function). For example, fields such as cognitive and behavioral neuroscience could not exist if the brain was not composed of specific types of cells, and the basic concepts of pharmacology could not exist if it was not known that a change at the cellular level can affect an entire organism. These applications extend into the ecological levels as well. For example, DDT's direct insecticidal effect occurs at the subcellular level, but affects higher levels up to and including multiple ecosystems. Theoretically, a change in one atom could change the entire biosphere.

Chemical element

A chemical element is a species of atom having the same number of protons in their atomic nuclei (that is, the same atomic number, or Z). For example, the atomic number of oxygen is 8, so the element oxygen consists of all atoms which have exactly 8 protons.

118 elements have been identified, of which the first 94 occur naturally on Earth with the remaining 24 being synthetic elements. There are 80 elements that have at least one stable isotope and 38 that have exclusively radionuclides, which decay over time into other elements. Iron is the most abundant element (by mass) making up Earth, while oxygen is the most common element in the Earth's crust.Chemical elements constitute all of the ordinary matter of the universe. However astronomical observations suggest that ordinary observable matter makes up only about 15% of the matter in the universe: the remainder is dark matter; the composition of this is unknown, but it is not composed of chemical elements.

The two lightest elements, hydrogen and helium, were mostly formed in the Big Bang and are the most common elements in the universe. The next three elements (lithium, beryllium and boron) were formed mostly by cosmic ray spallation, and are thus rarer than heavier elements. Formation of elements with from 6 to 26 protons occurred and continues to occur in main sequence stars via stellar nucleosynthesis. The high abundance of oxygen, silicon, and iron on Earth reflects their common production in such stars. Elements with greater than 26 protons are formed by supernova nucleosynthesis in supernovae, which, when they explode, blast these elements as supernova remnants far into space, where they may become incorporated into planets when they are formed.The term "element" is used for atoms with a given number of protons (regardless of whether or not they are ionized or chemically bonded, e.g. hydrogen in water) as well as for a pure chemical substance consisting of a single element (e.g. hydrogen gas). For the second meaning, the terms "elementary substance" and "simple substance" have been suggested, but they have not gained much acceptance in English chemical literature, whereas in some other languages their equivalent is widely used (e.g. French corps simple, Russian простое вещество). A single element can form multiple substances differing in their structure; they are called allotropes of the element.

When different elements are chemically combined, with the atoms held together by chemical bonds, they form chemical compounds. Only a minority of elements are found uncombined as relatively pure minerals. Among the more common of such native elements are copper, silver, gold, carbon (as coal, graphite, or diamonds), and sulfur. All but a few of the most inert elements, such as noble gases and noble metals, are usually found on Earth in chemically combined form, as chemical compounds. While about 32 of the chemical elements occur on Earth in native uncombined forms, most of these occur as mixtures. For example, atmospheric air is primarily a mixture of nitrogen, oxygen, and argon, and native solid elements occur in alloys, such as that of iron and nickel.

The history of the discovery and use of the elements began with primitive human societies that found native elements like carbon, sulfur, copper and gold. Later civilizations extracted elemental copper, tin, lead and iron from their ores by smelting, using charcoal. Alchemists and chemists subsequently identified many more; all of the naturally occurring elements were known by 1950.

The properties of the chemical elements are summarized in the periodic table, which organizes the elements by increasing atomic number into rows ("periods") in which the columns ("groups") share recurring ("periodic") physical and chemical properties. Save for unstable radioactive elements with short half-lives, all of the elements are available industrially, most of them in low degrees of impurities.


The curie (symbol Ci) is a non-SI unit of radioactivity originally defined in 1910. According to a notice in Nature at the time, it was named in honour of Pierre Curie, but was considered at least by some to be in honour of Marie Curie as well.It was originally defined as "the quantity or mass of radium emanation in equilibrium with one gram of radium (element)" but is currently defined as: 1 Ci = 3.7×1010 decays per second after more accurate measurements of the activity of 226Ra (which has a specific activity of 3.66×1010 Bq/g.)

In 1975 the General Conference on Weights and Measures gave the becquerel (Bq), defined as one nuclear decay per second, official status as the SI unit of activity.


1 Ci = 3.7×1010 Bq = 37 GBqand

1 Bq ≅ 2.703×10−11 Ci ≅ 27 pCiWhile its continued use is discouraged by National Institute of Standards and Technology (NIST) and other bodies, the curie is still widely used throughout the government, industry and medicine in the United States and in other countries.

At the 1910 meeting which originally defined the curie, it was proposed to make it equivalent to 10 nanograms of radium (a practical amount). But Marie Curie, after initially accepting this, changed her mind and insisted on one gram of radium. According to Bertram Boltwood, Marie Curie thought that 'the use of the name "curie" for so infinitesimally small [a] quantity of anything was altogether inappropriate.'The power in milliwatts emitted by one curie of radiation can be calculated by taking the number of MeV for the radiation times approximately 5.93.

A radiotherapy machine may have roughly 1000 Ci of a radioisotope such as caesium-137 or cobalt-60. This quantity of radioactivity can produce serious health effects with only a few minutes of close-range, unshielded exposure.

Ingesting even a millicurie is usually fatal (unless it is a very short-lived isotope). For example, the LD-50 for ingested polonium-210 is 240 μCi, about 53.5 nanograms.

The typical human body contains roughly 0.1 μCi (14 mg) of naturally occurring potassium-40. A human body containing 16 kg of carbon (see Composition of the human body) would also have about 24 nanograms or 0.1 μCi of carbon-14. Together, these would result in a total of approximately 0.2 μCi or 7400 decays per second inside the person's body (mostly from beta decay but some from gamma decay).

Elsie Widdowson

Elsie Widdowson (21 October 1906 – 14 June 2000), was a British dietitian and nutritionist. She and Dr Robert McCance were responsible for overseeing the government-mandated addition of vitamins to food and wartime rationing in Britain during World War II.

Human body

The human body is the structure of a human being. It is composed of many different types of cells that together create tissues and subsequently organ systems. They ensure homeostasis and the viability of the human body.

It comprises a head, neck, trunk (which includes the thorax and abdomen), arms and hands, legs and feet.

The study of the human body involves anatomy, physiology, histology and embryology. The body varies anatomically in known ways. Physiology focuses on the systems and organs of the human body and their functions. Many systems and mechanisms interact in order to maintain homeostasis, with safe levels of substances such as sugar and oxygen in the blood.

The body is studied by health professionals, physiologists, anatomists, and by artists to assist them in their work.

Hydrostatic weighing

Hydrostatic weighing, also referred to as "underwater weighing", "hydrostatic body composition analysis", and "hydrodensitometry" is a technique for measuring the mass per unit volume of a living person's body. It is a direct application of Archimedes' principle, that an object displaces its own volume of water.

Mineral (nutrient)

In the context of nutrition, a mineral is a chemical element required as an essential nutrient by organisms to perform functions necessary for life. However, the four major structural elements in the human body by weight (oxygen, hydrogen, carbon, and nitrogen), are usually not included in lists of major nutrient minerals (nitrogen is considered a "mineral" for plants, as it often is included in fertilizers). These four elements compose about 96% of the weight of the human body, and major minerals (macrominerals) and minor minerals (also called trace elements) compose the remainder.

Minerals, as elements, cannot be synthesized biochemically by living organisms. Plants get minerals from soil. Most of the minerals in a human diet come from eating plants and animals or from drinking water. As a group, minerals are one of the four groups of essential nutrients, the others of which are vitamins, essential fatty acids, and essential amino acids. The five major minerals in the human body are calcium, phosphorus, potassium, sodium, and magnesium. All of the remaining elements in a human body are called "trace elements". The trace elements that have a specific biochemical function in the human body are sulfur, iron, chlorine, cobalt, copper, zinc, manganese, molybdenum, iodine and selenium.Most chemical elements that are ingested by organisms are in the form of simple compounds. Plants absorb dissolved elements in soils, which are subsequently ingested by the herbivores and omnivores that eat them, and the elements move up the food chain. Larger organisms may also consume soil (geophagia) or use mineral resources, such as salt licks, to obtain limited minerals unavailable through other dietary sources.

Bacteria and fungi play an essential role in the weathering of primary elements that results in the release of nutrients for their own nutrition and for the nutrition of other species in the ecological food chain. One element, cobalt, is available for use by animals only after having been processed into complex molecules (e.g., vitamin B12) by bacteria. Minerals are used by animals and microorganisms for the process of mineralizing structures, called "biomineralization", used to construct bones, seashells, eggshells, exoskeletons and mollusc shells.

Properties of metals, metalloids and nonmetals

The chemical elements can be broadly divided into metals, metalloids and nonmetals according to their shared physical and chemical properties. All metals have a shiny appearance (at least when freshly polished); are good conductors of heat and electricity; form alloys with other metals; and have at least one basic oxide. Metalloids are metallic-looking brittle solids that are either semiconductors or exist in semiconducting forms, and have amphoteric or weakly acidic oxides. Typical nonmetals have a dull, coloured or colourless appearance; are brittle when solid; are poor conductors of heat and electricity; and have acidic oxides. Most or some elements in each category share a range of other properties; a few elements have properties that are either anomalous given their category, or otherwise extraordinary.


Rationing is the controlled distribution of scarce resources, goods, or services, or an artificial restriction of demand. Rationing controls the size of the ration, which is one's allowed portion of the resources being distributed on a particular day or at a particular time. There are many forms of rationing, and in western civilization people experience some of them in daily life without realizing it.Rationing is often done to keep price below the equilibrium (market-clearing) price determined by the process of supply and demand in an unfettered market. Thus, rationing can be complementary to price controls. An example of rationing in the face of rising prices took place in the various countries where there was rationing of gasoline during the 1973 energy crisis.

A reason for setting the price lower than would clear the market may be that there is a shortage, which would drive the market price very high. High prices, especially in the case of necessities, are undesirable with regard to those who cannot afford them. Traditionalist economists argue, however, that high prices act to reduce waste of the scarce resource while also providing incentive to produce more.

Rationing using ration stamps is only one kind of non-price rationing. For example, scarce products can be rationed using queues. This is seen, for example, at amusement parks, where one pays a price to get in and then need not pay any price to go on the rides. Similarly, in the absence of road pricing, access to roads is rationed in a first come, first served queueing process, leading to congestion.

Authorities which introduce rationing often have to deal with the rationed goods being sold illegally on the black market.

Science and inventions of Leonardo da Vinci

Leonardo da Vinci (1452–1519) was an Italian polymath, regarded as the epitome of the "Renaissance Man", displaying skills in numerous diverse areas of study. Whilst most famous for his paintings such as the Mona Lisa and the Last Supper, Leonardo is also renowned in the fields of civil engineering, chemistry, geology, geometry, hydrodynamics, mathematics, mechanical engineering, optics, physics, pyrotechnics, and zoology.

While the full extent of his scientific studies has only become recognized in the last 150 years, he was, during his lifetime, employed for his engineering and skill of invention. Many of his designs, such as the movable dikes to protect Venice from invasion, proved too costly or impractical. Some of his smaller inventions entered the world of manufacturing unheralded. As an engineer, Leonardo conceived ideas vastly ahead of his own time, conceptually inventing the parachute, an improved version of the helicopter, an armored fighting vehicle, the use of concentrated solar power, a calculator, a rudimentary theory of plate tectonics and the double hull . In practice, he greatly advanced the state of knowledge in the fields of anatomy, astronomy, civil engineering, optics, and the study of water (hydrodynamics).

Leonardo's most famous drawing, the Vitruvian Man, is a study of the proportions of the human body, linking art and science in a single work that has come to represent Renaissance Humanism.

Traditional Chinese medicines derived from the human body

Li Shizhen's (1597) Bencao gangmu, the classic materia medica of traditional Chinese medicine (TCM), included 35 human drugs, including organs, bodily fluids, and excreta. Crude drugs derived from the human body were commonplace in the early history of medicine. Some of these TCM human drug usages are familiar from alternative medicine, such as medicinal breast milk and urine therapy. Others are uncommon, such as the "mellified man", which was a foreign nostrum allegedly prepared from the mummy of a holy man who only ate honey during his last days and whose corpse had been immersed in honey for 100 years.

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