Latest from the Blog
Human Skin
WRITTEN BYF. John G. EblingSee All ContributorsProfessor of Zoology, 1968–82; Independent Research Worker in Dermatology, University of Sheffield, England. Coeditor of and contributor to Textbook of Dermatology.See Article History Human skin, in human anatomy, the covering, or integument, of the body’s surface that both provides protection and receives sensory stimuli from the external environment. The skin consists of three layers…
Human Renal system
WRITTEN BYJames Scott RobsonSee All ContributorsEmeritus Professor of Medicine, University of Edinburgh; Consultant Physician, Edinburgh Royal Infirmary. Author of numerous articles on acid-base and electrolyte metabolism and renal disorders.See Article History Renal system, in humans, organ system that includes the kidneys, where urine is produced, and the ureters, bladder, and urethra for the passage, storage, and voiding of urine. BRITANNICA…
Human Cardiovascular system
WRITTEN BYStanley W. JacobSee All ContributorsGerlinger Professor of Surgery, Oregon Health Sciences University, Portland. Author of Structure and Function in Man.See Article History Human cardiovascular system, organ system that conveys blood through vessels to and from all parts of the body, carrying nutrients and oxygen to tissues and removing carbon dioxide and other wastes. It is a closed tubular system in which…
Human Digestive system
WRITTEN BYWilliam T. KeetonSee All ContributorsLiberty Hyde Bailey Professor of Biology, Cornell University, Ithaca, New York, 1969–80. Author of Biological Science; Elements of Biological Science.Last Updated: Nov 4, 2020 See Article History Human digestive system, system used in the human body for the process of digestion. The human digestive system consists primarily of the digestive tract, or the series of structures and…
Human evolution
WRITTEN BYRussell Howard TuttleRussell H. Tuttle is an active Professor of Anthropology, Evolutionary Biology, History of Science and Medicine and the College at the University of Chicago. He conducted pioneering functional morphological…See Article History Human evolution, the process by which human beings developed on Earth from now-extinct primates. Viewed zoologically, we humans are Homo sapiens, a culture-bearing upright-walking species that lives on the…
Human Nervous system
WRITTEN BYCharles R. NobackSee All ContributorsEmeritus Professor of Anatomy and Cell Biology, College of Physicians and Surgeons, Columbia University. Coauthor of The Human Nervous System and others.See Article History Human nervous system, system that conducts stimuli from sensory receptors to the brain and spinal cord and conducts impulses back to other parts of the body. As with other higher vertebrates, the…
Human Respiratory system
WRITTEN BYRobert A. KlockeSee All ContributorsProfessor of Medicine and Physiology; Chief, Pulmonary Division, State University of New York at Buffalo. Coauthor of Normal and Abnormal Lung Function.See Article History Human respiratory system, the system in humans that takes up oxygen and expels carbon dioxide. The Design Of The Respiratory System The human gas-exchanging organ, the lung, is located in the…
Human Sensory reception
WRITTEN BYCarl PfaffmannVincent and Brooke Astor Professor of Physiological Psychology, Rockefeller University, New York City, 1980–83. Editor of Olfaction and Taste, proceedings of the Third International Symposium on…See Article History Human sensory reception, means by which humans react to changes in external and internal Ancient philosophers called the human senses “the windows of the soul,” and Aristotle described at least five…
Human Skeleton
WRITTEN BYWarren AndrewProfessor of Anatomy, Indiana University, Indianapolis, 1958–82. Author of Textbook of Comparative Histology.See Article History Human skeleton, the internal skeleton that serves as a framework for the body. This framework consists of many individual bones and cartilages. There also are bands of fibrous connective tissue—the ligaments and the tendons—in intimate relationship with the parts of the skeleton. This article is concerned primarily with the gross…
Human body
WRITTEN BYThe Editors of Encyclopaedia BritannicaEncyclopaedia Britannica’s editors oversee subject areas in which they have extensive knowledge, whether from years of experience gained by working on that content or via study for an advanced degree….See Article History Human body, the physical substance of the human organism, composed of living cells and extracellular materials and organized into tissues, organs, and…
Geology
WRITTEN BYBrian Frederick WindleySee All ContributorsProfessor of Geology, University of Leicester, England. Author of The Evolving Continents.See Article History Alternative Titles: geological science, geological sciences Geology, the fields of study concerned with the solid Earth. Included are sciences such as mineralogy, geodesy, and stratigraphy. An introduction to the geochemical and geophysical sciences logically begins with mineralogy, because Earth’s rocks are composed…
Life
WRITTEN BYDorion SaganSee All ContributorsGeneral partner, Sciencewriters, Amherst, Massachusetts. Coauthor of Slanted Truths: Essays on Gaia, Symbiosis, and Evolution; What Is Life?; Cracking the Aging Code; and others.See Article History Life, living matter and, as such, matter that shows certain attributes that include responsiveness, growth, metabolism, energy transformation, and reproduction. Although a noun, as with other defined entities, the word life might be better…
Plants – Kingdom Plantae
WRITTEN BYGeorge M. WoodwellSee All ContributorsDirector and President, Woods Hole Research Center, Massachusetts. Lecturer in Ecology, School of Forestry and Environmental Studies, Yale University. Coauthor of Biotic Feedbacks in the Global Climatic…See Article History Alternative Titles: Embryophyta, Metaphyta, Plantae Plant, (kingdom Plantae), any multicellular eukaryotic life-form characterized by (1) photosynthetic nutrition (a characteristic possessed by all plants except some parasitic plants…
Animals – Kingdom Animalia
WRITTEN BYLeigh M. Van ValenSee All ContributorsProfessor of Ecology and Evolution, University of Chicago.See Article History Alternative Title: Animalia Animal, (kingdom Animalia), any of a group of multicellular eukaryotic organisms (i.e., as distinct from bacteria, their deoxyribonucleic acid, or DNA, is contained in a membrane-bound nucleus). They are thought to have evolved independently from the unicellular eukaryotes. Animals…
Plant cell
WRITTEN BYThe Editors of Encyclopaedia BritannicaEncyclopaedia Britannica’s editors oversee subject areas in which they have extensive knowledge, whether from years of experience gained by working on that content or via study for an advanced degree….See Article History Plant cell, the basic unit of all plants. Plant cells, like animal cells, are eukaryotic, meaning they have a membrane-bound…
Cell
WRITTEN BYRonald A. LaskeySee All ContributorsCharles Darwin Professor of Animal Embryology, University of Cambridge. Editor of Higher Order Structure in the Nucleus and others.See Article History Alternative Title: cell system Cell, in biology, the basic membrane-bound unit that contains the fundamental molecules of life and of which all living things are composed. A single cell is often a complete…
List of chemical elements
WRITTEN BYThe Editors of Encyclopaedia BritannicaEncyclopaedia Britannica’s editors oversee subject areas in which they have extensive knowledge, whether from years of experience gained by working on that content or via study for an advanced degree….See Article History A chemical element is any substance that cannot be decomposed into simpler substances by ordinary chemical processes. Elements are the…
Chemical compound
Print Cite Share MoreWRITTEN BYRichard O.C. NormanSee All ContributorsRector, Exeter College, University of Oxford. Professor of Chemistry, University of York, England, 1956–87. Author of Principles of Organic Synthesis.See Article History Chemical compound, any substance composed of identical molecules consisting of atoms of two or more chemical elements. BRITANNICA QUIZIns and Outs of ChemistryWhat element is almost as light as hydrogen? All the matter in…
Reaction types
The electronic features of functional groups are responsible for the types of reactions that are characteristic of each group (see above Functional groups). Because there is a great deal of similarity in the electronic characteristics of the different functional groups, there is a corresponding similarity in the types of reaction that different groups undergo. Just as…
Organic compounds
In general, organic compounds are substances that contain carbon (C), and carbon atoms provide the key structural framework that generates the vast diversity of organic compounds. All things on the Earth (and most likely elsewhere in the universe) that can be described as living have a crucial dependence on organic compounds. Foodstuffs—namely, fats, proteins, and carbohydrates—are organic compounds, as are such vital substances as hemoglobin, chlorophyll, enzymes, hormones, and vitamins. Other materials…
Inorganic compounds
Inorganic compounds include compounds that are made up of two or more elements other than carbon, as well as certain carbon-containing compounds that lack carbon-carbon bonds, such as cyanides and carbonates. Inorganic compounds are most often classified in terms of the elements or groups of elements that they contain. Oxides, for example, can be either ionic or molecular. Ionic oxides…
Lawrencium – Lr
WRITTEN BYLester MorssAdjunct Professor, Department of Chemistry, University of Maryland, College Park, Maryland.See Article History Alternative Titles: Lr, element 103 Lawrencium (Lr), synthetic chemical element, the 14th member of the actinoid series of the periodic table, atomic number 103. Not occurring in nature, lawrencium (probably as the isotope lawrencium-257) was first produced (1961) by chemists Albert Ghiorso, T. Sikkeland, A.E. Larsh, and R.M. Latimer at the University…
Nobelium – No
WRITTEN BYLester MorssAdjunct Professor, Department of Chemistry, University of Maryland, College Park, Maryland.See Article History Alternative Titles: No, element 102 Nobelium (No), synthetic chemical element of the actinoid series of the periodic table, atomic number 102. The element was named after Swedish chemist Alfred Nobel. BRITANNICA QUIZ118 Names and Symbols of the Periodic Table QuizCm Not occurring in nature, nobelium was first claimed by an…
Mendelevium – Md
WRITTEN BYLester MorssAdjunct Professor, Department of Chemistry, University of Maryland, College Park, Maryland.See Article History Alternative Titles: Md, element 101 Mendelevium (Md), synthetic chemical element of the actinoid series of the periodic table, atomic number 101. It was the first element to be synthesized and discovered a few atoms at a time. Not occurring in nature, mendelevium (as the isotope mendelevium-256) was discovered (1955) by American chemists Albert…
Fermium – Fm
WRITTEN BYLester MorssAdjunct Professor, Department of Chemistry, University of Maryland, College Park, Maryland.See Article History Alternative Titles: Fm, element 100 Fermium (Fm), synthetic chemical element of the actinoid series of the periodic table, atomic number 100. Fermium (as the isotope fermium-255) is produced by the intense neutron irradiation of uranium-238 and was first positively identified by American chemist Albert Ghiorso and coworkers at Berkeley, California, in debris taken from the…
Einsteinium – Es
WRITTEN BYLester MorssAdjunct Professor, Department of Chemistry, University of Maryland, College Park, Maryland.See Article History Alternative Title: Es Einsteinium (Es), synthetic chemical element of the actinoid series of the periodic table, atomic number 99. Not occurring in nature, einsteinium (as the isotope einsteinium-253) was first produced by intense neutron irradiation of uranium-238 during the detonation of nuclear weapons. This isotope was identified in December 1952 by Albert Ghiorso and coworkers at Berkeley,…
Californium – Cf
WRITTEN BYLester MorssAdjunct Professor, Department of Chemistry, University of Maryland, College Park, Maryland.See Article History Alternative Title: Cf Californium (Cf), synthetic chemical element of the actinoid series of the periodic table, atomic number 98. Not occurring in nature, californium (as the isotope californium-245) was discovered (1950) by American chemists Stanley G. Thompson, Kenneth Street, Jr., Albert Ghiorso, and Glenn T. Seaborg at the University of California, Berkeley, as a product…
Berkelium – Bk
WRITTEN BYLester MorssAdjunct Professor, Department of Chemistry, University of Maryland, College Park, Maryland.See Article History Alternative Title: Bk Berkelium (Bk), synthetic chemical element of the actinoid series of the periodic table, atomic number 97. Not occurring in nature, berkelium (as the isotope berkelium-243) was discovered in December 1949 by American chemists Stanley G. Thompson, Albert Ghiorso, and Glenn T. Seaborg at the University of California, Berkeley, as a product…
Curium – Cm
WRITTEN BYLester MorssAdjunct Professor, Department of Chemistry, University of Maryland, College Park, Maryland.See Article History Alternative Title: Cm Curium (Cm), synthetic chemical element of the actinoid series of the periodic table, atomic number 96. Unknown in nature, curium (as the isotope curium-242) was discovered (summer 1944) at the University of Chicago by American chemists Glenn T. Seaborg, Ralph A. James, and Albert Ghiorso in a sample of a plutonium isotope, plutonium-239,…
Americium – Am
WRITTEN BYLester MorssAdjunct Professor, Department of Chemistry, University of Maryland, College Park, Maryland.See Article History Alternative Title: Am Americium (Am), synthetic chemical element (atomic number 95) of the actinoid series of the periodic table. Unknown in nature, americium (as the isotope americium-241) was artificially produced from plutonium-239 (atomic number 94) in 1944 by American chemists Glenn T. Seaborg, Ralph A. James, Leon O. Morgan, and Albert Ghiorso…
Neptunium – Np
WRITTEN BYLester MorssAdjunct Professor, Department of Chemistry, University of Maryland, College Park, Maryland.See Article History Alternative Title: Np Neptunium (Np), radioactive chemical element of the actinoid series of the periodic table that was the first transuranium element to be artificially produced, atomic number 93. Though traces of neptunium have subsequently been found in nature, where it is not primeval but produced by neutron-induced transmutation reactions in uranium ores, American physicist Edwin M. McMillan and…
Uranium – U
WRITTEN BYLester MorssAdjunct Professor, Department of Chemistry, University of Maryland, College Park, Maryland.See Article History Alternative Title: U Uranium (U), radioactive chemical element of the actinoid series of the periodic table, atomic number 92. It is an important nuclear fuel. BRITANNICA QUIZ118 Names and Symbols of the Periodic Table QuizMd Uranium constitutes about two parts per million of Earth’s crust. Some important uranium minerals are pitchblende (impure U3O8), uraninite (UO2), carnotite (a potassium uranium vanadate), autunite (a calcium uranium phosphate), and torbernite (a copper uranium phosphate).…
Protactinium – Pa
WRITTEN BYLester MorssAdjunct Professor, Department of Chemistry, University of Maryland, College Park, Maryland.See Article History Alternative Title: Pa Protactinium (Pa), radioactive chemical element of the actinoid series of the periodic table, rarer than radium; its atomic number is 91. It occurs in all uranium ores to the extent of 0.34 part per million of uranium. Its existence was predicted by Russian chemist Dmitry Mendeleyev in his 1871 periodic table.…
Thorium – Th
WRITTEN BYLester MorssAdjunct Professor, Department of Chemistry, University of Maryland, College Park, Maryland.See Article History Alternative Title: Th Thorium (Th), radioactive chemical element of the actinoid series of the periodic table, atomic number 90; it is a useful nuclear reactor fuel. Thorium was discovered (1828) by Swedish chemist Jöns Jacob Berzelius. It is silvery white but turns gray or black on exposure to air. It is…
Chemistry
WRITTEN BYAlan J. RockeSee All ContributorsProfessor of History, Case Western Reserve University, Cleveland, Ohio, U.S. Author of The Quiet Revolution: Hermann Kolbe and the Science of Organic Chemistry and other books.See Article History Chemistry, the science that deals with the properties, composition, and structure of substances (defined as elements and compounds), the transformations they undergo, and the energy that…
Development Of Atomic Theory
The concept of the atom that Western scientists accepted in broad outline from the 1600s until about 1900 originated with Greek philosophers in the 5th century BCE. Their speculation about a hard, indivisible fundamental particle of nature was replaced slowly by a scientific theory supported by experiment and mathematical deduction. It was more than 2,000 years before modern physicists realized…
Lanthanoid, lanthanide
WRITTEN BYThe Editors of Encyclopaedia BritannicaEncyclopaedia Britannica’s editors oversee subject areas in which they have extensive knowledge, whether from years of experience gained by working on that content or via study for an advanced degree….See Article History Alternative Title: lanthanide Lanthanoid, also called lanthanide, any of the series of 15 consecutive chemical elements in the periodic table from lanthanum to lutetium (atomic numbers 57–71). With scandium and yttrium,…
Lutetium – Lu
WRITTEN BYThe Editors of Encyclopaedia BritannicaEncyclopaedia Britannica’s editors oversee subject areas in which they have extensive knowledge, whether from years of experience gained by working on that content or via study for an advanced degree….See Article History Alternative Title: Lu Lutetium (Lu), chemical element, a rare-earth metal of the lanthanide series of the periodic table, that is the densest and the highest-melting…
Ytterbium – Yb
WRITTEN BYThe Editors of Encyclopaedia BritannicaEncyclopaedia Britannica’s editors oversee subject areas in which they have extensive knowledge, whether from years of experience gained by working on that content or via study for an advanced degree….See Article History Alternative Title: Yb Ytterbium (Yb), chemical element, a rare-earth metal of the lanthanide series of the periodic table. https://f1233f0d83fb89d1ac07e05943b4081d.safeframe.googlesyndication.com/safeframe/1-0-37/html/container.htmlBRITANNICA QUIZ118 Names and Symbols of the…
Thulium – Tm
WRITTEN BYThe Editors of Encyclopaedia BritannicaEncyclopaedia Britannica’s editors oversee subject areas in which they have extensive knowledge, whether from years of experience gained by working on that content or via study for an advanced degree….See Article History Alternative Title: Tm Thulium (Tm), chemical element, a rare-earth metal of the lanthanide series of the periodic table. thuliumThulium.RTCEncyclopædia Britannica, Inc.BRITANNICA QUIZ118 Names and Symbols of…
Erbium – Er
WRITTEN BYThe Editors of Encyclopaedia BritannicaEncyclopaedia Britannica’s editors oversee subject areas in which they have extensive knowledge, whether from years of experience gained by working on that content or via study for an advanced degree….See Article History Alternative Title: Er Erbium (Er), chemical element, a rare-earth metal of the lanthanide series of the periodic table. BRITANNICA QUIZ118 Names and Symbols of the Periodic…
Holmium – Ho
WRITTEN BYThe Editors of Encyclopaedia BritannicaEncyclopaedia Britannica’s editors oversee subject areas in which they have extensive knowledge, whether from years of experience gained by working on that content or via study for an advanced degree….See Article History Alternative Title: Ho Holmium (Ho), chemical element, a rare-earth metal of the lanthanide series of the periodic table. https://4efc8ff9320772180773a2c49f0184e4.safeframe.googlesyndication.com/safeframe/1-0-37/html/container.htmlBRITANNICA QUIZ118 Names and Symbols of the…
Science 