Visionlearning Glossary

(January 28, 1909 — February 11, 1972) A Canadian-American geneticist. He received his M.D. from McGill University in 1932, at the age of 23. Working with Oswald Avery and Maclyn McCarty, MacLeod showed that changes in the form or function of bacteria are caused by changes in DNA. The Avery-McCarty-MacLeod experiment was vital in the discovery that genetic material is contained in DNA, not in protein. Later in life, MacLeod became involved in health issues related to the Second World War, such as the microbial diseases typhus fever, malaria, and pneumonia, which posed serious threats to military personnel.

Used in the following modules: DNA I

(Portuguese: Fernão de Magalhães, c. 1480 – April 27, 1521) A Portuguese explorer who became a Spanish national so that he could search for a westward route to the Spice Islands (modern Indonesia) for King Charles of Spain. Magellan's expedition of 1519–1522 was the first to sail from the Atlantic Ocean to the Pacific Ocean, and the first to cross the Pacific. The expedition completed a circumnavigation of the globe, but Magellan was killed in battle in the Philippines. Magellan named the Pacific Ocean (from Latin, meaning the peaceful ocean), which he reached via what he named the Straits of Magellan. He also named the Magellanic penguin; he was the first European to describe it. He is remembered as one of the great explorers, and the Magellanic clouds, nearby dwarf galaxies visible from the southern hemisphere are named after him.

Molten rock below the surface of the earth.

Used in the following modules: Ideas in Science: Scientific Controversy, Minerals I, Minerals II, Plate Tectonics I, Plate Tectonics II, Research Methods: Description, The Rock Cycle

English ordained minister and economist born in Dorking, Surrey (1766-1834). In 1798 he published his Essay on Population, suggesting that a given population will always exceed its food supply, and it would therefore be counterproductive to provide starving populations with food. Instead, he argued, social equality must be achieved through other means, such as universal suffrage and state-funded education for the poor. For further information see Thomas Robert Malthus.

Used in the following modules: Charles Darwin II

A United States project initiated in August 1942 that was responsible for developing atomic technology, and specifically an atomic bomb, during World War II.

The middle portion of the interior of the earth, starting below the crust at 5-70 km below the earth’s surface and continuing to a depth of 2900 km. The mantle is composed mainly of the rock peridotite.

Used in the following modules: Earth Structure, Ideas in Science: Scientific Controversy, Minerals I, Minerals III, Plate Tectonics II

a fundamental property of matter which is a numerical measure of the inertia of an object or the amount of matter that an object contains. The mass of an object is different from its weight as mass is independent of the gravitational field exerted on an object.

Used in the following modules: Adaptation, Atomic Theory I, Atomic Theory II, Chemical Equations, Classic Experiment: Meselson and Stahl, Data: Uncertainty, Error, and Confidence, Density, Earth's Atmosphere, Gravity, Matter, Minerals I, Minerals II, Nuclear Chemistry, Research Methods: Description, Research Methods: The Practice of Science, Scientific Communication: Peer Review, Scientific Institutions and Societies, The Metric System, The Mole, The Nature of Scientific Knowledge, The Scientific Method

A spectrometer that measures the composition of samples by analyzing the mass to charge ratio (m/z) of components in the sample. To do this, the sample introduced into the spectrometer is ionized under high energy, and the various ions are then seperated in a magnetic field and measured. The specific m/z signature of each ion is then used to identify the parent element or compound. For additional information, see the Wikipedia's definition of mass spectrometry.

Used in the following modules: Minerals I, Minerals II, Research Methods: Description

derived from or related to one’s mother.

Used in the following modules: Absorption, Distribution and Storage of Chemicals, Genetics I

English marine geophysicist, born in Porlock, Somerset (1931-1997). In 1962, Matthews participated in the International Indian Ocean Expedition and made a detailed survey of a submarine ridge that showed that the pattern of magnetic polarity of sea floor rocks surrounding the ridge was symmetric. This discovery contributed to the widespread acceptance of the plate tectonic theory. He also studied the structure and evolution of continental crust using deep crustal seismics. For further information, see Drummond Matthews.

Used in the following modules: Plate Tectonics I

Scottish theoretical physicist and mathematician born in Edinburgh (1831-1879). Maxwell developed the classical electromagnetic theory, which synthesized previously unrelated observations, experiments and equations of electricity and magnetism. In 1864, Maxwell wrote A Dynamical Theory of the Electromagnetic Field, in which he proposed that light is a wave. He also described what is now known as Maxwellian distribution, a statistical way of describing the kinetic theory of gases. For further information see James Clerk Maxwell.

Used in the following modules: Light I, Light II

The abbreviation for millibar

Used in the following modules: Earth's Atmosphere

(June 9, 1911 – January 2, 2005) An American physician and geneticist who specialized in infectious diseases. McCarty is remembered for discovering, with Oswald Avery and Colin MacLeod, that DNA is responsible for changes in form and function of bacteria. McCarty’s later work focused on rheumatic fever and its relationship to the Streptococcus bacteria, and he pioneered the now-standard medical practice of using protein levels in blood to measure rheumatic inflammation.

Used in the following modules: DNA I

In statistics, mean commonly refers to the arithmetic mean, also called the average, which is one measure of the mid-point of a dataset. The mean and median approach one another in datasets that approach a normal distribution, but can differ substantially in datasets with skewed distributions. Compare to median. The mean is calculated by obtaining the sum of the values in a dataset and dividing that sum by the number of data points, as in the formulas:

Used in the following modules: Absorption, Distribution and Storage of Chemicals, Acids and Bases, Cells, Charles Darwin I, Charles Darwin II, Charles Darwin III, Chemical Equations, Data: Analysis and Interpretation, Data: Statistics, Data: Uncertainty, Error, and Confidence, Data: Using Graphs and Visual Data, Density, Earth's Atmosphere, Educational Web Design, Energy, Ideas in Science: Scientific Controversy, Minerals I, Minerals II, Research Methods: Comparison, Research Methods: Experimentation, The Carbon Cycle, The Hydrologic Cycle, The Nitrogen Cycle, Unit Conversion, Wave Mathematics

English biologist and essayist born in Brazil (1915-1987). Though he initially studied zoology, he became more interested in medicine in graduate school. With Sir Frank MacFarlane Burnet, Medawar won the Nobel Prize for Physiology or Medicine in 1960 “for discovery of acquired immunological tolerance”; Medawar’s work concerned skin grafting and other organ transplants in humans. In his later years, he became a prolific author about the nature of science, and is well known for his essays “The Art of the Soluble” and “The Phenomenon of Man”. For more information, see Peter Medawar.

Used in the following modules: Creativity in Science

In statistics, the median is the value separating the upper half from the lower half of a dataset. In other words, it is the middle value of the data when they are arranged in order of magnitude. The median is a characteristic of a dataset comparable to the mean. The median and mean approach one another in datasets that approach the normal distribution, but can differ substantially in datasets with skewed distributions.

Used in the following modules: Data: Statistics

(Mpc) a numerical value of distance in space. 1 Mpc = 1 million paresecs, where one parsec equals 3.26 light years, or ~19 trillion miles.

(13 August 1844 – 26 August 1895) A Swiss physician and biologist. An attack of typhoid fever left him partially deaf, and he felt this would be a disadvantage as a doctor, so decided to pursue physiological chemistry instead. He is remembered for isolating nucleic acids from white blood cells, one of many steps that made possible the discovery that DNA carries genetic material. In addition, Meischer proved that breathing is regulated by carbon dioxide concentrations in the blood.

Austrian Augustinian monk and scientist born in Heizendorf (now Hynice, Chech Republic)(1822-1884). In 1856, Mendel wrote Versuche über Pflanzen-Hybride (Treatises on Plant Hybrids), which detailed his observations on the inheritance of various traits in cross-bred pea plants and presented his principles of hereditary transmission. Unfortunately, the importance of his work was not recognized until after his death. For further information see Gregor Mendel.

Used in the following modules: Creativity in Science, DNA I, From Stable Chromosomes to Jumping Genes, Genetics I, Genetics II, Ideas in Science: Theories, Hypotheses, and Laws, Scientific Institutions and Societies, Scientists and the Scientific Community

Russian inventor and chemist born in Tobolsk, Siberia (1834-1907). Mendeleev’s most famous work is the development of the periodic table of elements, and his prediction of properties of elements that were, at that time, not yet discovered. In 1869, Mendeleev helped found the Russian Chemical Society. He researched in many fields including physics, hydrodynamics, meteorology, and chemical technology. For further information see Dmitri Mendeleev.

Used in the following modules: The Periodic Table of Elements

1. The lowermost portion of the mantle. 2. The layer of the atmosphere above the stratosphere, where temperature decreases with altitude.

Used in the following modules: Earth Structure, Earth's Atmosphere

A sequence of biochemical reactions in living organisms that converts food into energy used to drive other biological processes. Also, the sequence of transformations foreign compounds undergo inside a living cell.

Used in the following modules: Adaptation, Carbohydrates, Cells, Classic Experiment: Meselson and Stahl, Research Methods: Experimentation, The Carbon Cycle

Formed through the processes involved in metamorphism, which include deep burial, exposure to high temperatures and pressures, and interactions with hydrothermal fluids. Metamorphic rocks are generally considered to have a parent rock, or protolith, which can be any rock type. The minerals and textures that are produced through metamorphism are indicative of both the protolith and the metamorphic environment.

Used in the following modules: Minerals III, The Rock Cycle

Physical and chemical changes to rocks that occur below the earth’s surface. These changes are caused by increased temperature, increased pressure, and the presence of hydrothermal fluids, and result in the growth and reorientation of crystals in the rock. Metamorphism does not include melting - once magma forms, the resulting rock will be igneous.

English natural philosopher and geologist, born in Nottinghamshire, (1724-1793). In 1750 he published A Treatise of Artificial Magnets, detailing his observations on the variations in forces between magnetic poles. He also demonstrated radiation pressure, adding support to Christian Huygens’ argument that light consists of waves. For further information see John Michell.

Used in the following modules: Gravity

American physicist, born in Strelno, Prussia (1852-1931). He is remembered for his work in optics, particularly for his early, extremely accurate experiments to determine the velocity of light. Michelson invented the interferometer, which he used to determine the effect of Earth’s motion on the observed velocity of light. He was also interested in astronomy, and, using his interferometer, accurately measured the diameter of the star Betelgeuse. He was awarded a Nobel Prize in physics in 1907. For further information see Albert Michelson.

Used in the following modules: Light II

A linear, elevated region of the ocean floor where magma is upwelling, extruding, and new crust is forming. The ridges are often referred to by their more specific names: Mid-Atlantic Ridge, East Pacific Rise, etc.

Used in the following modules: Earth Structure, Plate Tectonics I, Plate Tectonics II

a period of European history from the 5th century to the 15th century. The Middle Ages follow the fall of the Western Roman Empire in 476 and are marked by depopulation, migration from urban centers, and increasing frequency of barbarian invasions. Key events include the Crusades, during which Europeans attempted to recapture the Holy Land, and the development of the serf system, which enabled systematic agriculture to begin again. Agriculture was widely affected due to climate change, resulting in frequent famines. In addition, the Black Death (which may have been the bubonic plague) spread rapidly across Europe, killing 30-60% of the population by the mid-14th century. With the resulting decrease in the labor force, due to death by disease or hunger, landlords were forced to offer higher wages to entice peasants to work in their fields. The end of the Middle Ages is generally considered to be 1453, the date of the Turks’ conquest of Constantinople.

Used in the following modules: Charles Darwin I, Minerals II, Taxonomy I

A unit of measurement of atmospheric pressure equivalent to 1 gram per square centimeter. Average sea level pressure is 1013 mb, equivalent to one Atmosphere.

Used in the following modules: Earth's Atmosphere

A naturally formed, inorganic solid with a specific chemical composition and characteristic crystal structure. Examples of minerals include quartz (SiO₂), salt (also called halite, NaCl), graphite (C). Rocks are formed of one or more minerals.

Used in the following modules: Charles Darwin I, Data: Statistics, Ideas in Science: Scientific Controversy, Matter, Matter: States of Matter, Minerals I, Minerals II, Minerals III, Plate Tectonics I, Research Methods: Description, The Carbon Cycle, The Rock Cycle

Conversion into an inorganic form.

Used in the following modules: The Nitrogen Cycle

The commonly used abbreviation of the Mohorovicic Discontinuity, the boundary between the crust and the mantle.

Used in the following modules: Earth Structure

The boundary within the earth between the crust and the mantle, as indicated by the refraction and velocity change of seismic waves recognized by Andrija Mohorovicic. The depth of the Mohorovicic Discontinuity is ~5-7 km below oceanic crust and ~10-70 km below continental crust.

Used in the following modules: Earth Structure

Croatian meteorologist and geophysicst born in Volosko (1857-1921). In 1901, Mohorovičić was appointed head on the meteorological service of Croatia and Slavonia. He upgraded the services to European standards, and expanded the work of the observatory into seismology, geomagnetism and gravitation. Mohorovičić discovered the existence of S and P seismic waves, which propagate through the Earth at different velocities. From seismic refractions, Mohorovičić discovered a discontinuity between the less dense rocks of the crust and denser rocks of the mantle, now called the Mohorovičić discontinuity (known more commonly as the Moho). For more information, see Andrija Mohorovicic.

Used in the following modules: Earth Structure

German geologist and mineralogist born in Gernrode (1773-1839). In 1802, after studying at the Mining Academy in Freiberg, Saxony, Mohs moved Austria, where he was hired to identify minerals in a private collection. In order to do this, he classified the minerals by their physical characteristics, rather than their chemical compositions (as was usually done). He developed the Moh’s hardness scale, a relative scale of the hardness of minerals that remains a useful way to identify minerals in the field. For further information, Friedrich Mohs.

Used in the following modules: Minerals II

An amount equal to Avogadro’s number or 6.02 × 10²³. One mole of atoms is equal to 6.02 × 10²³atoms.

Used in the following modules: Acids and Bases, Chemical Equations, The Mole

The formula weight of a compound, given by summing the atomic weights of atoms in the compound. Given in grams, the molecular weight is the weight of one mole of molecules in a compound.

Used in the following modules: Absorption, Distribution and Storage of Chemicals, Chemical Equations, The Mole

A particle formed by the chemical bonding of two or more atoms. The molecule is the smallest particle of a chemical compound that retains the chemical properties of the compound.

Used in the following modules: Absorption, Distribution and Storage of Chemicals, Acids and Bases, Carbohydrates, Cells, Chemical Bonding, Chemical Equations, Classic Experiment: Meselson and Stahl, Creativity in Science, Density, DNA I, DNA II, DNA III, Earth's Atmosphere, Fats and Proteins, Matter: States of Matter, Minerals I, Nuclear Chemistry, Organic Chemistry, Research Methods: Description, Research Methods: Modeling, Scientists and the Scientific Community, The Carbon Cycle, The Metric System, The Mole, The Nitrogen Cycle, Water

Any molecule that may become chemically bonded to other molecules of the same type to form a larger molecule called a polymer.

(September 25, 1866 – December 4, 1945) An American embryologist who won the Nobel Prize in Physiology or Medicine in 1933 for his discoveries about the role that chromosomes play in heredity. Morgan’s most important book, with several coauthors, The Mechanism of Mendelian Heredity, was published in 1915, and became a fundamental work in the field of genetics. Morgan’s later work focused on embryology and on encouraging the use of genetics research and a mechanistic approach in all fields of biology.

Used in the following modules: Genetics I

a story, idea or concept invented with a purpose. Myths are generally intended to explain the relationship between gods or natural forces and humans. The events in myths are often impossible, but myths contain important social or religious information for the population that has created them.

Used in the following modules: Charles Darwin I, Research Methods: Description